Home, Sweet Home!
For decades, people have installed nest boxes to give birds safe places to raise their young. These structures help make up for the mature trees, standing deadwood, and natural cavities that have disappeared from many neighborhoods and managed landscapes. And, of course, they also let us enjoy watching wildlife close to home.
Just as a well-maintained feeder can provide extra food when natural resources are scarce, a properly designed nest box can help species affected by habitat loss. It offers chickadees, bluebirds, wrens, Tree Swallows, and other cavity-nesting birds a breeding site that might otherwise be unavailable.
Nest boxes also provide wonderful opportunities for environmental education. Building one with children, choosing an appropriate location, and observing its occupants year after year can create a lasting connection with nature. The project becomes even more meaningful when children learn that different species require different entrance sizes, dimensions, heights, and habitats—and that a decorative birdhouse is not always a safe home.
Fortunately, wildlife shelters are no longer viewed mainly as tools for capturing or exploiting animals. Today, birdhouses, bat boxes, bee hotels, and other artificial shelters can be designed with the animals’ welfare in mind. With suitable materials, good ventilation and drainage, protection from predators, and regular maintenance, our furred, winged, and feathered guests can find a home without coming to harm.
Natural Nesting Materials Are Always Welcome
Providing birds with a place to raise their young is one thing. Making sure they can find the materials needed to build a safe nest is another. What looks like ordinary yard debris to us may be valuable construction material to them.
Mud Builders Around Our Homes
A colony of Cliff Swallows may construct dozens of gourd-shaped mud nests beneath a bridge, culvert, or broad roof overhang. Barn Swallows also rely on mud, usually building open cups on sheltered ledges inside barns, sheds, and porches. Eastern Phoebes combine mud with moss, leaves, and grass when nesting in protected corners around buildings.
For these birds, the shortage is not necessarily flying insects. Suitable mud and undisturbed nesting surfaces may be harder to find. Smooth modern walls, sealed eaves, intensive landscaping, and paved surroundings offer few places to gather wet soil or attach a nest. A small patch of damp, pesticide-free earth can therefore be surprisingly useful, especially near open areas where swallows forage. Cliff and Barn Swallows commonly nest on human-made structures when mud and suitable ledges are available.
The best way to help nesting birds is to give them a quiet, secure yard with abundant natural vegetation. Dense shrubs, native grasses, fallen leaves, and standing plant stems provide both concealment and a wide selection of building materials. Birds may collect slender twigs, dry grasses, bark fibers, moss, leaves, pine needles, plant down, or small pieces of straw, depending on the species and the type of nest being constructed.
Rather than placing these materials in a tightly packed container, leave them scattered naturally around the garden. Allow some leaves to remain beneath shrubs, retain a few broken twigs, and postpone cutting back native grasses and perennial stems until spring. This lets each bird select material of the proper size, strength, and flexibility. Maintaining several layers of native vegetation also supplies protected nesting sites and places where birds can forage.
Mud is especially valuable to American Robins, Eastern Phoebes, and Barn and Cliff Swallows. During dry weather, a shallow area of bare soil can be moistened occasionally so that it remains workable—but it should never become a deep container in which birds could become trapped. Avoid using soil contaminated by pesticides, fertilizers, oil, road salt, or other chemicals.
Older gardening advice sometimes recommends offering cotton, wool, human hair, pet fur, yarn, or dryer lint. These materials are no longer considered safe choices. Long fibers can wrap around a nestling’s legs, wings, or neck, while human hair longer than about an inch presents a similar entanglement hazard. Pet fur may contain residues from flea-and-tick treatments, and dryer lint may contain detergents and synthetic microfibers; it also loses its structure when wet. Fishing line, ribbon, plastic strips, twine, and loose netting should likewise be removed from the yard.
Loose, naturally shed feathers may be collected by some birds, but there is rarely any need to supply them. A wildlife-friendly garden already contains nearly everything a capable nest builder requires. The safest assistance is not a basket of manufactured scraps, but a healthy landscape in which natural materials remain available.
Natural nesting materials can make a yard especially attractive in late winter and spring. Offer small amounts of dry grass, pine needles, thin twigs, moss, soft plant fibers, strips of native bark, and a few clean, naturally shed feathers. Place them loosely in an open basket or clean wire suet cage hung where birds can reach them easily.
Avoid yarn, string, fishing line, plastic fibers, dryer lint, cotton batting, and human or pet hair. These materials can wrap around a bird’s feet or become dangerously tangled around nestlings. Dryer lint also absorbs water and may contain residues from detergents and fabric treatments.
Swallows need mud
For Barn Swallows and Cliff Swallows, wet soil is one of the most valuable nesting materials a yard can provide. Each spring, these long-distance migrants return from wintering grounds in Mexico, Central America, and South America. Many come back to the same barn, bridge, porch, or nesting colony they used in previous years.
Adult birds often repair an existing nest, while young swallows must build one from the beginning. Either way, they may need hundreds of small mud pellets. When natural puddles disappear during dry weather, finding enough suitable mud can become difficult.
The best mixture contains plenty of fine clay and silt, with only a modest amount of sand. When it dries, it should hold together firmly rather than crumble. A shallow mud patch made with untreated local soil or natural clay can remain useful for days if it is watered regularly.
Choose a safe place in the open, preferably near an active swallow nesting site but away from roads, contaminated runoff, outdoor cats, and areas treated with pesticides or fertilizers.
Make a swallow mud patch
- Choose a shallow depression, large plant saucer, tray, or patch of bare ground in an open, visible location.
- Add about an inch of untreated clay-rich soil. Avoid potting mixes containing fertilizer, perlite, pesticides, or moisture-retaining chemicals.
- Shape the edges into gentle slopes so small birds can land and walk to the mud easily.
- Add water until the soil becomes soft and sticky but not deeply flooded.
- Mix in a little local soil and a few short pieces of dry grass to create a varied texture.
- Keep the patch damp throughout the nesting season, especially during warm, dry weather.
- Watch from a distance. Swallows may begin collecting mud surprisingly quickly once they discover it.
During nesting season, birds carefully gather many different construction materials. Small twigs, grasses, bark fibers, moss, plant down, feathers, and mud may all become part of a nest. Supplying safe, natural materials in modest amounts can help birds complete this demanding work.
A simple mud patch can be especially valuable to Barn Swallows and Cliff Swallows. Keep it shallow, accessible, and consistently moist so the birds can collect small beakfuls and carry them back to their nests.
The Origins and Evolution of Nest Boxes
People have provided artificial nesting places for birds for centuries, although their original motives were not always conservation-minded. Today, nest boxes serve a very different purpose—and have become valuable tools for protecting wildlife and studying the natural world.
There are many reasons to install a nest box on a porch, fence, barn, or backyard tree. Unlike some early forms of bird housing, however, modern boxes are not intended to provide people with eggs or young birds. Their purpose is to offer a safe nesting cavity to species that might otherwise struggle to find one.
In North America, people have long encouraged certain birds to live close to their homes. Native peoples in parts of the eastern United States hung hollow gourds near settlements for Purple Martins, and European settlers later continued the practice. Farmers also welcomed swallows, martins, and other insect-eating birds around barns and fields. By the late nineteenth and early twentieth centuries, growing interest in bird protection and nature study encouraged Americans to put up nesting structures for a much wider variety of species.
Researchers soon discovered that artificial cavities could help birds in places where natural nest sites were disappearing. Many birds do not excavate their own holes. Instead, they depend on cavities created by woodpeckers or formed naturally in old, damaged, or decaying trees. When forests are cleared, dead trees are removed, or older woodlands are replaced by young, uniform stands, those cavities become scarce.
Nest boxes cannot replace mature forests or standing dead trees, but they can partially offset a local shortage of nesting sites. They have played an especially important role in the recovery of Eastern and Western Bluebirds, whose populations suffered from habitat loss and competition from nonnative European Starlings and House Sparrows. Properly designed boxes are also used by Tree Swallows, chickadees, titmice, nuthatches, wrens, woodpeckers, Wood Ducks, American Kestrels, and several species of owls.
Over time, nest-box designs have become more specialized. We now know that the dimensions of the floor, the depth of the cavity, the diameter and position of the entrance, and the height and location of the box all influence which birds are likely to use it. A box suitable for a chickadee would be far too small for a Wood Duck, while an oversized entrance could expose small songbirds to predators or larger competitors.
Researchers have also learned that the box must protect its occupants from rain and overheating. A good design includes drainage holes, ventilation near the roof, a securely attached top, an untreated interior, and a rough surface below the entrance so young birds can climb out. Perches are generally unnecessary and may give predators or aggressive birds an advantage. Where climbing predators are common, the box should be mounted on a pole fitted with an effective baffle rather than nailed directly to a tree.
Nest boxes have become important scientific tools as well. Because their contents can be inspected with relatively little disturbance, they allow researchers and trained volunteers to study egg-laying dates, clutch size, hatching success, nestling growth, migration timing, and the effects of weather and climate. Long-term monitoring programs have produced valuable information about changes in breeding seasons and bird populations across the continent.
They are also used in conservation projects for declining species and in carefully planned habitat restoration. Forest managers sometimes install boxes for cavity-nesting birds, bats, or small mammals while young trees mature and natural cavities develop. Still, artificial structures should be treated as a supplement—not as an excuse to remove old trees, snags, native vegetation, or other essential habitat.
A weathered nesting gourd or old wooden birdhouse may survive for years, but a damaged structure can admit rain, trap heat, or expose its occupants to predators. Every nest box should be inspected and repaired before the breeding season.
Modern boxes may be made from durable wood, recycled plastic, or wood-concrete blends. Longevity is useful, but good ventilation, drainage, safe dimensions, and easy access for monitoring are even more important.
Why Hang a Gourd Beside the House?
Long before manufactured birdhouses became common, hollow gourds offered a simple way to provide nesting cavities. After the fruit had dried, people could cut a small entrance hole, remove the seeds and pulp, and suspend the shell from a pole or wooden frame.
In eastern North America, this practice became closely associated with Purple Martins. These large swallows readily accepted gourds placed near human settlements, where their active colonies and bubbling calls made them familiar seasonal neighbors. The original reasons for attracting them were probably both practical and cultural. Martins may have helped alert people to approaching hawks or crows, and their presence was likely appreciated around homes and cultivated land. Claims that martins consume large numbers of mosquitoes are exaggerated, however; most of their prey consists of larger flying insects captured high in the air.
Over many generations, Purple Martins in much of the eastern United States became increasingly dependent on human-provided nesting sites. Natural cavities remain important in parts of the West, but eastern populations now commonly breed in hanging gourds or multi-compartment martin houses.
Traditional gourds have largely been replaced by wooden houses and molded plastic nesting chambers, yet the basic principle remains unchanged: people provide a dark, sheltered cavity with a small entrance, and the birds decide whether it meets their needs.
The tradition has not disappeared. In many rural communities and backyards, martin colonies are still watched over by dedicated landlords who lower the housing for regular checks, remove invasive competitors, replace wet nesting material, and record the progress of each brood. In this way, one of North America’s oldest forms of bird housing has evolved from a practical custom into a partnership centered on stewardship, observation, and conservation.
Nest Boxes: Why Put Them Up? Still not convinced?
After feeding birds throughout the winter and offering them nutritious food, why say goodbye when spring arrives? Now comes the most exciting part of the year: helping the birds in your yard raise their young.
Once your attention becomes fixed on the small, dark entrance of a nest box, you will understand how rewarding it can be to provide a safe nesting place for a pair of chickadees. You may watch the adults carry moss and plant fibers inside, deliver insects to their nestlings, and finally guide their young into the outside world.
Cavity-nesting birds can, of course, find nest sites on their own. Many of the species that visit our yards originally nested in forests, where they used holes created by woodpeckers or natural decay. Some have adapted surprisingly well to living near people, especially where gardens and parks provide abundant insects, seeds, and native plants.
Suitable nesting cavities, however, have not increased along with bird populations in developed areas. In many places, they have become much harder to find. Urban expansion, intensive farming, and the removal of dead or aging trees have eliminated countless nesting sites. Old trees filled with cracks and hollows are far less common than they were only a few decades ago.
Leaving safe dead trees and branches standing is one of the best ways to support cavity-nesting wildlife. Where that is not possible, a properly designed nest box can help replace some of the habitat that has been lost. Chickadees, wrens, nuthatches, bluebirds, and Tree Swallows may all use boxes when the entrance size, interior dimensions, and surrounding habitat meet their needs.
A nest box is therefore more than a garden decoration. It can offer birds a secure place to reproduce while giving you a remarkable opportunity to observe an entire nesting season—from the first inspection of the box to the day the young birds take flight.
In the screenshot below we can see a Carolina chickadee feeding its nestlings. This curious year-round resident is common across much of the southeastern United States. It naturally inhabits deciduous and mixed woodlands but also does well in parks and wooded neighborhoods. The female usually lays about three to ten eggs and generally raises one brood each year.
Building nest boxes with children is a fun, hands-on way to learn about birds—and a workshop can be organized almost anywhere. Why not hold one at a school, library, nature center, or community garden for World Migratory Bird Day?
In many parts of the United States, dead trees are removed, old barns are sealed, hedgerows disappear, and new buildings leave few cracks or cavities. Where, then, can bluebirds, chickadees, wrens, swallows, and small owls raise their young?
The familiar enclosed birdhouse is only one kind of artificial nest. There are open-fronted shelves for robins and phoebes, nesting cups for swallows, apartment-style houses for Purple Martins, towers for Chimney Swifts, platforms for Ospreys, floating rafts for loons, and artificial burrows for Burrowing Owls. When natural nest sites are scarce, these structures can provide valuable alternatives.
However, there is no universal birdhouse. The dimensions, entrance size, mounting height, surrounding habitat, and distance between boxes must suit the intended species. A safe nest box should be made from thick, untreated wood and include drainage, ventilation, a rough interior surface, an overhanging roof, and a panel that opens for monitoring. Exterior perches are unnecessary, and boxes are usually safest on a metal pole fitted with an effective predator guard.
Nest boxes cannot replace mature trees, standing deadwood, native vegetation, or healthy insect populations. Preserve safe snags whenever possible, grow regionally native plants, avoid pesticides, and keep pet cats indoors. Separate structures should be used for bats and native bees because their shelter requirements are very different from those of birds. Even a well-designed bat house can be harmful if it overheats or is installed incorrectly.
ARTIFICIAL NESTS FOR ALL KINDS OF BIRDS
U.S. birds that tend to use nest boxes and similar structures
The species attracted will depend on the region, habitat, structure design, and placement. Cornell Lab of Ornithology’s NestWatch provides species-specific plans for boxes, shelves, platforms, nesting cones, and other artificial structures.
| Common name | Scientific name | Common name | Scientific name |
|---|---|---|---|
| Osprey | Pandion haliaetus | Brown-headed Nuthatch | Sitta pusilla |
| Common Loon | Gavia immer | Pygmy Nuthatch | Sitta pygmaea |
| Wood Duck | Aix sponsa | Eastern Bluebird | Sialia sialis |
| Hooded Merganser | Lophodytes cucullatus | Western Bluebird | Sialia mexicana |
| Bufflehead | Bucephala albeola | Mountain Bluebird | Sialia currucoides |
| American Kestrel | Falco sparverius | Black-capped Chickadee | Poecile atricapillus |
| Barred Owl | Strix varia | Carolina Chickadee | Poecile carolinensis |
| Eastern Screech-Owl | Megascops asio | Chestnut-backed Chickadee | Poecile rufescens |
| Western Screech-Owl | Megascops kennicottii | Tufted Titmouse | Baeolophus bicolor |
| Northern Saw-whet Owl | Aegolius acadicus | Oak Titmouse | Baeolophus inornatus |
| Burrowing Owl | Athene cunicularia | House Wren | Troglodytes aedon |
| Purple Martin | Progne subis | Bewick’s Wren | Thryomanes bewickii |
| Chimney Swift | Chaetura pelagica | Carolina Wren | Thryothorus ludovicianus |
| Tree Swallow | Tachycineta bicolor | Prothonotary Warbler | Protonotaria citrea |
| Violet-green Swallow | Tachycineta thalassina | Lucy’s Warbler | Leiothlypis luciae |
| Barn Swallow | Hirundo rustica | Ash-throated Flycatcher | Myiarchus cinerascens |
| Northern Flicker | Colaptes auratus | Great Crested Flycatcher | Myiarchus crinitus |
| Red-bellied Woodpecker | Melanerpes carolinus | Eastern Phoebe | Sayornis phoebe |
| Downy Woodpecker | Dryobates pubescens | Say’s Phoebe | Sayornis saya |
| Brown Creeper | Certhia americana | American Robin | Turdus migratorius |
| White-breasted Nuthatch | Sitta carolinensis | Mourning Dove | Zenaida macroura |
| Red-breasted Nuthatch | Sitta canadensis | — | — |
THE IDEAL NEST BOX: Function, Durability, and Safety
Five features of a good nest box
- It is sturdy and built to last.
- It opens easily for monitoring and cleaning without disturbing the nesting attempt.
- It protects its occupants from rain, wind, moisture, and excessive heat.
- It reduces access by raccoons, squirrels, snakes, cats, and other predators.
- Its design is simple and appropriate for the intended bird species.
A damaged or poorly designed nest box can become a deadly trap. Leaks, overheating, loose panels, or easy predator access may leave eggs and nestlings more vulnerable than they would be in a natural cavity. Inspect every box regularly, and repair, replace, or remove it whenever it is no longer safe.
Durability is one of the most important qualities a nest box can have. You may install it before the breeding season and begin checking it the following spring, but remember that it will remain outdoors through years of sun, rain, snow, and changing temperatures. If properly built and maintained, it may be used by several generations of birds.
Choose untreated cedar, pine, or fir, with walls thick enough to insulate the interior. A sloping, overhanging roof helps keep out rain, while ventilation near the top and drainage holes in the floor prevent dangerous heat and moisture from building up. One wall should open securely so the box can be inspected and cleaned after the nesting season. Avoid decorative perches, which birds do not need and predators may use. Whenever possible, mount the box on a smooth metal pole fitted with a predator guard rather than directly on a tree or fence.
Walls that are too thin can turn a nest box into a dangerous heat trap during warm weather and provide little protection during cold spring nights. Metal, thin plastic, cardboard, and lightweight decorative wood are poor choices because they do not regulate temperature well. For most backyard species, the safest material is untreated cedar, pine, cypress, or fir at least 3/4 inch thick. A well-designed box should also have ventilation near the top, drainage in the floor, and an extended, sloping roof that sheds rain.
A nest box will protect its occupants only if it remains sturdy and dry for many breeding seasons. Loose joints, warped boards, and weak mounting hardware can allow rain inside—or cause the entire box to fall while eggs or nestlings are present. Galvanized or exterior-grade screws generally hold more securely than nails, which may loosen as the wood expands and contracts. A recessed floor, overlapping roof, and tightly fitted walls help keep the nesting chamber dry. The box should also open easily from one side or the front so it can be inspected and cleaned without dismantling it.
Untreated wood can weather naturally and does not need to be painted. Where additional protection is necessary, apply a light-colored, water-based exterior finish only to the outside and allow it to cure completely before installing the box. Never paint the interior or use pressure-treated lumber. Dark colors should be avoided in sunny locations because they absorb more heat.
Predators require special attention. Raccoons, cats, snakes, squirrels, and other animals may climb a tree or post, enlarge an entrance, or reach a paw into the nesting chamber. One of the most effective defenses is to mount the box on a free-standing metal pole fitted with a properly designed cone or stovepipe baffle. An entrance extender or Noel-style guard can make it harder for a predator to reach eggs and nestlings. The roof should project well beyond the entrance, and the box should never have an exterior perch: native cavity-nesting birds do not need one, but predators may use it. NestWatch data indicate that boxes equipped with predator guards have, on average, greater nesting success than unguarded boxes.
The box’s appearance is far less important than whether it suits the bird you hope to attract. Chickadees, wrens, bluebirds, Tree Swallows, kestrels, screech-owls, and Wood Ducks all require different entrance sizes, floor dimensions, depths, mounting heights, habitats, and spacing. A box designed for an Eastern Bluebird will not serve the same purpose as one intended for a Wood Duck or an owl.
The entrance hole is especially important because its diameter helps determine which birds can enter. But it should never be considered in isolation: the depth below the entrance, size of the floor, ventilation, drainage, mounting method, and surrounding habitat are also essential. The best guiding principle is the right box in the right place. Bluebird boxes belong in open country with low vegetation, while chickadees and many wrens generally prefer boxes near woodland edges, shrubs, or mature trees.
Avoid choosing a birdhouse simply because it is inexpensive, brightly painted, or shaped like a tiny cottage. Many decorative models sold in gift shops and big-box stores have thin walls, oversized entrances, useless perches, poor ventilation, no drainage, and no way to open the box for cleaning. They may look charming in a garden, but they should be treated as ornaments rather than wildlife habitat.
A nest box is not meant primarily to please its human owner. Its purpose is to provide a safe substitute for a natural tree cavity. The comfort, protection, and survival of the birds must always come first.
BUILD IT OR BUY IT?
Build It Yourself
- A basic wooden box is neither especially difficult nor expensive to make.
- Building one can be a rewarding family project, particularly with children.
- You can follow a species-specific plan and adapt the mounting system to your property.
- Damaged parts are usually easy to repair or replace.
- Small mistakes in entrance size, depth, ventilation, or drainage can make the box unsafe or unsuitable.
- Poor joints and lightweight materials may deteriorate quickly.
- The project requires suitable tools, careful measurements, and time.
Buy a Nest Box
- Boxes from reputable bird-conservation groups or specialty retailers often use tested, species-specific designs.
- Good commercial boxes usually include thick wood, durable hardware, ventilation, drainage, and an opening panel for monitoring and cleaning.
- Many are designed to accept pole baffles and other predator guards.
- A knowledgeable seller can help match the box to the birds and habitat in your region.
A properly constructed nest box may cost considerably more than a decorative birdhouse.
Most home woodworkers already have the basic tools needed to build a nest box: untreated 1-inch lumber—which is usually ¾ inch thick—a saw, drill/driver, exterior-grade screws, hinges, measuring tools, and sandpaper. A good box should also include drainage, ventilation, an overhanging roof, and a side or front panel that opens for inspection.
Where, When, and How?
Choosing the right location matters as much as building the box itself. A nest box must suit its intended bird, remain securely mounted, and provide protection from predators, storms, and excessive heat.
What are we trying to accomplish?
The first priority is to give cavity-nesting birds a safe place to raise their young. That sounds simple, but a successful nest box must balance several needs: the entrance should be easy for the birds to approach, the interior should remain dry and well ventilated, and the box should be accessible enough for responsible monitoring and maintenance.
Begin by deciding which native species you hope to attract. There is no universal birdhouse for every American backyard. Eastern, Western, and Mountain Bluebirds generally need boxes overlooking open ground; chickadees, titmice, and wrens are more closely associated with wooded yards and shrubby edges; Tree Swallows favor open areas, often near water; and Wood Ducks require much larger boxes close to suitable wetlands. Entrance size, box dimensions, mounting height, habitat, and spacing should all be selected for the target species.
How should it be mounted?
For most small backyard nest boxes, a smooth metal pole is the safest and most practical support. It is easier to protect than a tree trunk or wooden fence post and allows a cone or stovepipe baffle to be installed below the box. These guards can greatly reduce access by raccoons, snakes, squirrels, chipmunks, and other climbing predators. The pole should stand away from trees, fences, trellises, roofs, and overhanging branches that an animal could use as a launching point.
Fasten the box firmly so that it cannot twist or sway in strong winds. Its inspection panel must remain easy to open, but it should close with a secure latch so that raccoons or squirrels cannot pry it apart. Before driving rebar or a pole into the ground, have underground utility lines marked.
Mounting a box on a tree may be appropriate for certain woodland species, including some owls and flycatchers, but it is usually less protective for small songbirds. Tree trunks offer predators an easy climbing route, and an effective baffle is more difficult to install. Follow a species-specific plan rather than choosing a tree simply because it is convenient.
Every box should be firmly attached and easy for the owner to locate. When maintaining several boxes, number them discreetly and keep a record of their occupants, nesting dates, and condition.
Where and when should it be installed?
Habitat comes first. A perfectly constructed bluebird box placed deep inside dense woods is unlikely to succeed, just as a woodland chickadee box may be poorly positioned in the middle of an exposed field. Place the entrance toward the habitat the bird will use for arriving, feeding, and escaping rather than toward a busy road, doorway, or heavily traveled path.
There is no single compass direction that works throughout the United States. In many locations, facing the entrance away from prevailing winds and driving rain is most important. In hot regions, avoid an entrance and broad wall exposed to intense western afternoon sun; an east- or northeast-facing opening and afternoon shade can help prevent dangerous overheating. Boxes intended for open-country birds still need to be designed and positioned with summer heat in mind.
Height also depends on the species. Many bluebird boxes are mounted only a few feet above the ground, while screech-owl, kestrel, and Wood Duck boxes may be considerably higher. Do not place a box so high that routine inspection becomes unsafe. A lower box protected by a good pole and predator baffle is often more secure than an inaccessible box attached high in a tree.
Nest boxes may be installed at any time of year. Putting them up during fall or winter gives birds time to discover them before nesting begins, and some birds may use them as nighttime shelter during cold weather. Late winter is also a good time to inspect existing boxes, tighten loose hardware, clear blocked drainage holes, and make repairs.
Never clean or dismantle a box while birds are actively nesting. Once the breeding attempt has clearly ended, old material may be removed if appropriate for the species. Use mild soap and water only when necessary, rinse thoroughly, and allow the box to dry completely. Because nesting calendars vary greatly from Florida to Alaska, it is better to install a suitable box whenever it is ready than to wait for one supposedly perfect date.
Installing a nest box can involve some risk. Follow the placement and orientation recommendations for the species you hope to attract. Work from firm, level ground, use a stable ladder with another person present, and avoid dead or weakened trees. Never install a box on a utility pole or anywhere near overhead power lines.
A well-designed nest box is simple and sturdy. The entrance is high enough above the floor to keep a predator from easily reaching the nest, and there is no outside perch to assist raccoons, squirrels, or competing birds. Use untreated wood at least ¾ inch thick, provide ventilation near the top and drainage through the floor, and add a sloping roof that extends beyond the entrance. The inside surface below the hole should be rough or lightly grooved so fledglings can climb out. A hinged panel makes monitoring and cleaning easier.
In many American yards, the best mounting system is a free-standing metal pole fitted with a predator baffle. This is generally safer than attaching the box to a tree or fence post, where raccoons, snakes, squirrels, and outdoor cats may reach it more easily. As with most wildlife-friendly structures, simplicity is an advantage.
ENTRANCE-HOLE SIZE • each species has its own requirements
| Species | Diameter | Notes |
|---|---|---|
| Brown-headed Nuthatch | 1 in. (25 mm) | A southeastern species associated with mature, open pine woods. The small opening helps exclude larger competitors. |
| House Wren | 1 in. (25 mm) | Widespread and common around woodland edges, shrubby yards, parks, and farms. Place the box near natural cover. |
| Black-capped Chickadee | 1⅛ in. (29 mm) | Common across the northern United States. Best in wooded yards and forest edges, with the entrance facing away from prevailing winds. |
| Carolina Chickadee | 1⅛ in. (29 mm) | The typical chickadee of the Southeast and south-central states. Usually found near mature deciduous trees. |
| Tufted Titmouse | 1¼ in. (32 mm) | A familiar bird of eastern woodlands and wooded suburbs. Boxes should be spaced well apart because pairs defend nesting territories. |
| White-breasted Nuthatch | 1¼ in. (32 mm) | Uses boxes in mature deciduous woods, orchards, and wooded yards, especially where natural cavities are scarce. |
| Tree Swallow | 1⅜ in. (35 mm) | Best in open fields, meadows, or marshy areas, often near water. A roughened interior below the entrance helps young birds climb out. |
| Eastern or Western Bluebird | 1½ in. (38 mm) | Place in open habitat with low vegetation and a clear flight path. These boxes require regular monitoring because House Sparrows may take them over. |
| Mountain Bluebird | 1⁹⁄₁₆ in. (40 mm) | Found mainly in open country across the West. Mount the box on a guarded pole facing open habitat. |
The entrance diameter is only one part of a successful design. Interior depth, floor area, habitat, mounting height, spacing, shade, drainage, and protection from predators must also match the intended species. House Sparrows can enter holes about 1¼ inches wide, so larger boxes—especially those intended for bluebirds and swallows—should be checked regularly.
Build It Yourself
With a few basic tools and a suitable piece of lumber, you can build your own nest box by following the plans below. Nest boxes come in many sizes and styles, but this simple design is an excellent place to begin. It is easy to assemble, easy to maintain, and well suited to several small native cavity-nesting birds.
Nest Box with a Small Entrance Hole
This is the classic backyard nest box: straightforward to build and, when installed in the right habitat, likely to attract occupants. In much of the northern United States, Black-capped Chickadees are among the most likely residents; in the Southeast, their place is often taken by Carolina Chickadees. House Wrens, Bewick’s Wrens, and Red-breasted Nuthatches may also use a box of this size where their ranges and preferred habitats overlap.
Place the box near trees, shrubs, or woodland edges, but not where dense branches give squirrels, raccoons, cats, or snakes easy access. Mount it securely about 5–10 feet above the ground, preferably on a pole fitted with a predator guard. Face the entrance away from prevailing storms and, in hot climates, away from intense afternoon sun.
Use untreated cedar, pine, or another durable wood at least ¾ inch thick. Leave the interior unpainted and slightly rough so young birds can climb toward the entrance. Do not add a perch: native cavity nesters do not need one, and it may help predators or aggressive nonnative birds.
Chickadees are among the most likely occupants of this box. Depending on the species and location, incubation generally lasts about 12–13 days, and the nestlings remain in the cavity for roughly another 16–18 days. Most chickadees raise one brood per season, although nesting dates vary considerably across the country.
The Entrance Hole Matters
The diameter of the entrance determines which birds can use the box—and which ones are kept out.
A hole measuring 1⅛ inches in diameter is suitable for chickadees, small wrens, and Red-breasted Nuthatches. Its small size also helps exclude larger birds, including invasive House Sparrows and European Starlings. Drill the hole so that its center is at least 6 inches above the inside floor.
Add several shallow horizontal grooves beneath the entrance on the inside surface, or leave that surface rough-sawn, to help fledglings climb out.
Roof and Drainage
The roof should extend beyond the front and sides to shield the entrance from rain. A sloping roof sheds water more effectively, and mounting the entire box with a very slight forward tilt helps prevent rain from running inside.
Drill four small drainage holes near the corners of the floor. Leave narrow ventilation gaps beneath the roof or drill small ventilation holes high in both side panels. The roof or one side should open for inspection and annual cleaning, but it must fasten securely so predators cannot lift it.
Remove old nesting material after the breeding season, then brush out the interior. Avoid pesticides, disinfectant residues, mothballs, or treated nesting fibers.
Suggested Cutting Plan
Cut the pieces from one 1 × 8-inch board, 6 feet long. A nominal 1 × 8 board is actually about ¾ × 7¼ inches.
| Piece | Approximate length |
|---|---|
| Roof | 9 in |
| Back | 16 in |
| Front | 10 in |
| First side blank | 12 in |
| Second side blank | 10 in |
| Floor | 6 in |
Cut the upper edges of the side panels to match the roof slope. Position the floor slightly above the bottom edges of the walls so water can drain freely. Assemble the box with corrosion-resistant exterior screws rather than nails, which makes future repairs easier.
Before installing it, confirm that the entrance is smooth, the cleanout panel closes firmly, and no screw points protrude into the nesting chamber.
Nest box with a medium entrance hole
Although this box resembles the smaller models described earlier, it is intended for larger cavity-nesting birds. In wooded neighborhoods and along forest edges, possible occupants include Hairy Woodpeckers and, with a smaller entrance, Downy Woodpeckers. A Hairy Woodpecker box should have a floor approximately 6 × 6 inches, an interior depth of 12–15 inches, and a 1½-inch round entrance positioned 9–12 inches above the floor. For Downy Woodpeckers, reduce the floor to about 4 × 4 inches and the entrance to 1¼ inches.
Drainage becomes especially important as the entrance grows larger and admits more wind-driven rain. Recess the floor slightly above the bottom edges and drill at least four drainage holes, each ⅜–½ inch in diameter. A sloping roof should extend several inches beyond the front and sides, and ventilation openings should be placed near the top of both side walls.
Only when the box is intended for an excavating species such as a woodpecker should it contain loose material. Add coarse, dry shavings from untreated wood or small pieces of soft, decaying wood. These imitate the interior of a natural snag and allow the birds to remove material as part of their nesting behavior. Do not use expanded polystyrene, pressure-treated wood waste, or fine sawdust, which can retain moisture or introduce unsuitable materials. Downy Woodpeckers naturally leave their eggs resting on wood chips inside the cavity.
Nest Box with a Large Entrance Hole
If you have suitable habitat and would like to attract a larger native cavity-nesting bird, this is the type of box to build. Depending on your region, it may be used by American Kestrels, Eastern or Western Screech-Owls, Boreal Owls, or Northern Saw-whet Owls.
A proven North American design has an interior approximately 9⅝ by 11¼ inches and 17⅜ inches deep. The entrance can be a 3-by-4-inch oval or, more simply, a 3-inch round hole.
Use untreated pine or cedar boards with an actual thickness of about ¾ inch, or non-pressure-treated, exterior-grade CDX plywood. Approximately 10 linear feet of 1-by-12 lumber is required. Reclaimed wood may be used only when it is sound, sufficiently thick, and free from paint, preservatives, pressure treatment, or chemical residues. One side should open for monitoring and seasonal cleaning. Assemble the box with galvanized exterior screws.
Nest Box with a Special Entrance
Exterior-grade plywood can also be used for a much larger project: providing an artificial nesting cavity for an American Barn Owl. This box is more complex than a typical songbird house. In a building-mounted design, an interior divider creates a darker, more secluded nesting chamber behind the entrance.
Install the box securely in a quiet barn, shed, silo, or similar outbuilding, or mount it on a sturdy pole. The entrance should have a clear flight path leading toward grassland, marsh, ranchland, or mixed farmland where the owls can hunt. Cornell NestWatch recommends placing Barn Owl boxes 8–25 feet above the ground. Its current plan has a 4½-inch entrance, an interior depth of 16 inches, and a floor approximately 12⅜ × 22¾ inches. Avoid using rodenticides nearby, since poisoned rodents can also poison the owls that eat them.
A Ghost over the Fields
You may recognize an American Barn Owl by sound before you ever see one. It does not give the familiar deep hoot of many other owls. Instead, it produces harsh rasps, hisses, and eerie screeches. Its pale, heart-shaped face may appear almost ghostlike as it flies low over open fields at dusk. Barn Owls need extensive open habitat in which to hunt, so a nest box will be most useful in a rural or semi-rural landscape with suitable feeding grounds nearby.
Small Open-Front Nest Box
American Robins and phoebes often choose sheltered ledges, porch beams, bridge supports, and other partially enclosed sites rather than traditional birdhouses. This compact design imitates those locations. Unlike a cavity-style box with a round entrance hole, it has a broad opening across the upper front, giving the birds plenty of room to enter while making the nest easy to observe without lifting the roof. Cornell NestWatch recommends sheltered nest shelves for American Robins, Eastern Phoebes, and Say’s Phoebes.
The roof may slope from back to front or from one side to the other. When mounting the box, position the lower edge of the roof toward the direction from which rain can drain most safely. The entrance itself can face either left or right—or any compass direction—provided that it is protected from strong sun, prevailing storms, and heavy runoff.
Use an untreated 1 × 6-inch board, approximately 44 inches long and at least ¾ inch thick.
| Piece | Dimensions |
|---|---|
| Roof | 6 × 8 in. |
| Back | 6 × 12 in. |
| Floor | 6 × 4¾ in. |
| Tall side | 6 × 8 in. |
| Short side | 6 × 7 in. |
| Front retaining board | 6 × 4 in. |
The unequal side panels create a gentle side-to-side roof slope. Reverse their positions when assembling the box if you want the roof to drain in the opposite direction.
Kestrel Nest Box
This is the penthouse suite of the American Kestrel. Unlike birds that use open-front nesting shelves, this small falcon needs a fully enclosed cavity with a 3 × 4-inch oval entrance; a 3-inch round opening also works. Although designed for kestrels, the same box may occasionally attract Eastern or Western Screech-Owls and other small cavity-nesting owls, depending on the region.
Attracting a pair is never guaranteed, but the chances improve when the box is mounted 10–30 feet above the ground, facing south or east, with an unobstructed approach over pasture, meadow, orchard, or another open hunting area. Lone trees along field edges, sturdy posts, and quiet farm buildings can all provide suitable locations. Space kestrel boxes about half a mile apart.
Use untreated, weather-resistant lumber at least ¾ inch thick, such as pine or cedar. Provide ventilation near the top, drainage openings in the floor, an overhanging roof, and a securely latched hinged side for monitoring and annual cleaning. Add a shallow layer of coarse wood shavings because kestrels do not carry nesting material into the cavity themselves.
American Kestrels inhabit open country across much of North America. Look for them around grasslands, ranches, agricultural fields, woodland edges, deserts, and even towns, where they hunt insects, small mammals, reptiles, and other small prey from exposed perches or while hovering above the ground.
Towers for Chimney Swifts
The Chimney Swift is a familiar summer bird in towns and cities across much of the eastern United States. Long ago, these birds nested mainly inside large hollow trees, but today they depend heavily on old masonry chimneys and similar human-made structures. As traditional chimneys disappear or are capped, purpose-built swift towers can provide valuable replacement habitat.
A swift tower is unlike an ordinary birdhouse. It is a tall, narrow shaft, open at the top and closed at the bottom, that imitates the hollow interior of a tree or chimney. It may be built as a freestanding structure in a yard, park, school campus, or community garden, or incorporated into a new building. Because towers require a strong foundation and must withstand wind and weather, it is easiest to include them during construction or renovation. Plans should comply with local building codes, especially in areas affected by hurricanes, strong winds, or frost heaving.
The internal chamber should be at least 8 feet deep, although a height of 12 feet is more attractive and may also accommodate groups of roosting swifts during migration. The inside should be no narrower than about 14 inches. Swifts usually attach their nest to the lower third of the shaft, where it is better protected from direct sun and rain.
The interior surface must be rough enough for the birds to cling to and to support the small twig nest they fasten to the wall with saliva. Rough-sawn wood, textured plywood with horizontal grooves, masonry block, or brick with exposed mortar joints can work well. Smooth plastic, metal, or finished wood is unsuitable and may trap birds that cannot climb the slippery walls. The inside should remain unpainted and untreated.
Recommended dimensions
- Overall height: 8 feet minimum; 12 feet preferred
- Interior shaft: at least 14 × 14 inches
- Inner wall: rough-textured wood or unfinished masonry
- Wall construction: double wall with rigid insulation
- Top opening: no more than half the area of the shaft, positioned toward the north side
- Predator guard: a 24-inch band of smooth metal flashing near the top
- Bottom: removable panel with small ventilation holes
- Foundation: reinforced concrete sized for the tower and local soil conditions
Artificial Nests for Swallows
Barn Swallows and Cliff Swallows do not always accept artificial nests as readily as cavity-nesting birds accept nest boxes. These highly skilled builders usually prefer nests made from their own mud pellets. Still, a well-designed starter cup can attract them to a suitable site—especially where smooth walls, metal siding, or modern construction provide few natural attachment points.
Commercial wood-concrete swallow cups are the most durable option. You can also make a simple cup yourself, provided the finished nest is rough-textured, weather-resistant, securely mounted, and placed beneath a deep overhang.
1. Choose the Right Shape
Use a ball about 5 inches in diameter as a mold. Cover half of it to make an open cup for a Barn Swallow. For a Cliff Swallow, form a more enclosed shell with a small entrance near the upper edge.
Wrap the ball in reusable plastic film or apply a thin layer of petroleum jelly so the hardened shell can be removed easily.
2. Build the Nest Shell
For a lasting outdoor nest, use a lightweight, non-toxic mineral-based mortar or a commercially available wood-concrete mixture. Apply it over the mold until the wall is approximately ⅜ to ½ inch thick.
Keep the exterior irregular rather than perfectly smooth. A rough surface resembles a natural mud nest and gives birds something to grip when they add their own material.
3. Remove the Mold
Allow the material to cure completely. Carefully separate the shell from the ball and trim any sharp or unstable edges.
A Barn Swallow cup should remain open across the top. A Cliff Swallow cup should be more enclosed, with enough room for the adults to enter and turn inside. When possible, use a commercially produced cup designed for the intended species, since entrance dimensions and interior space are important.
4. Attach the Nest Securely
Fasten the cup to a vertical backboard made from untreated exterior-grade lumber. Add a small wooden roof above it to imitate a protected ledge.
Use corrosion-resistant screws and sturdy metal brackets rather than adhesive alone. The nest must support the adults, their growing young, and the extra mud the birds may add.
Install the structure beneath a broad eave or inside an open barn, shed, porch, or carport. Keep it away from doors, busy walkways, fans, machinery, cooking areas, bright nighttime lighting, and surfaces that become dangerously hot.
5. Adapt the Design to the Species
For Barn Swallows, leave the front and upper portion of the cup open. They favor sheltered structures with easy access to surrounding fields, lawns, wetlands, or other open feeding areas.
For Cliff Swallows, use a mostly enclosed nest with a small side entrance. Because Cliff Swallows are social and normally nest in colonies, several cups placed together beneath a large overhang may be more attractive than a single isolated nest.
A removable board below the nests can catch droppings, but leave enough space between the board and the nest entrance for unobstructed flight.
Well-Made Nest Boxes for Backyard Birds
Buying a professionally made nest box can be an excellent alternative to building one yourself. Reputable designs are based on the needs of particular North American birds rather than on appearance alone. You can find models intended for chickadees, wrens, nuthatches, bluebirds, swallows, flycatchers, owls, kestrels, and even cavity-nesting ducks.
A good commercial box should be durable, securely constructed, easy to open and clean, and appropriate for the species you hope to attract. The entrance size, interior dimensions, mounting height, surrounding habitat, and protection from predators are all more important than decorative details.
Beyond Wood
When buying a nest box, you can afford to be selective. Untreated wood—especially cedar, pine, cypress, or fir—remains one of the best materials because it resembles a natural tree cavity and provides useful insulation. Walls should generally be at least ¾ inch thick.
Some manufacturers offer boxes made from plastics, composite lumber, or other weather-resistant materials. These may last longer than ordinary wooden boxes, but durability alone does not make a box safe. Thin plastic, metal, ceramic, and lightweight decorative materials can become dangerously hot or fail to protect eggs and nestlings from sudden temperature changes. Any alternative material should be thick, well insulated, nontoxic, and designed specifically for nesting birds.
Whatever the material, look for ventilation openings near the roof, drainage holes in the floor, a deep roof overhang, and a hinged side or front for monitoring. The interior below the entrance should be rough or grooved so fledglings can climb out. Avoid boxes with an outside perch: native cavity nesters do not need one, and it may give predators easier access.
A hard outer surface can discourage squirrels or woodpeckers from enlarging the entrance, but it cannot replace proper predator protection. Raccoons, snakes, chipmunks, and free-roaming cats may still reach an exposed box. A freestanding metal pole fitted with a cone or stovepipe baffle is usually safer than mounting the box directly on a tree, fence, or building.
Some hanging designs shed rain well, but a swinging box can be difficult to stabilize and protect. For most backyard songbirds, a securely mounted box on a baffled metal pole is easier to monitor and offers better protection from climbing predators.
The Standard Nest Box
So-called general-purpose birdhouses are sold throughout the United States, but no single design is ideal for every bird. A box intended for a chickadee should not have the same entrance or interior depth as one made for a bluebird, flicker, or screech-owl.
The diameter of the entrance helps determine which birds can use the box. Its location matters just as much. Bluebird and Tree Swallow boxes belong in open country, lawns, pastures, or meadows. Chickadees and nuthatches generally prefer wooded yards or forest edges. Carolina Wrens favor shrubby areas, while Prothonotary Warbler boxes must be placed near or over wooded wetlands.
Commercial models may include entrance extensions, sloping roofs, recessed floors, predator guards, or internal climbing grooves. These are useful additions, provided they are part of a proven, species-appropriate design. Choose the bird first, confirm that it occurs in your region, and then select both the box and the location for that species.
Entrance-Hole Size
Typical round entrance diameters and some of the principal North American birds they accommodate:
1 inch — 25 mm
- House Wren
- Brown-headed Nuthatch
1⅛ inches — 29 mm
- Black-capped Chickadee
- Carolina Chickadee
- Chestnut-backed Chickadee
- Mountain Chickadee
1¼ inches — 32 mm
- Red-breasted Nuthatch
- White-breasted Nuthatch
- Tufted Titmouse
- Prothonotary Warbler
1⅜ inches — 35 mm
- Tree Swallow
- Violet-green Swallow
1½ inches — 38 mm
- Eastern Bluebird
- Western Bluebird
- Carolina Wren
1 9⁄16 inches — 40 mm
- Mountain Bluebird
1¾ inches — 44 mm
- Great Crested Flycatcher
- Ash-throated Flycatcher
House Sparrows can enter openings as small as 1¼ inches, while European Starlings can squeeze through openings around 1 9⁄16 inches. Both are invasive in the United States, and providing nest boxes specifically for them is discouraged. Entrance diameter alone cannot prevent every conflict, so boxes should be monitored regularly and managed according to local wildlife regulations.
SPECIAL NEST BOXES
Some specialized chickadee boxes have two or even three entrance holes. The additional daylight encourages the birds to build their nest toward the rear of the box, where eggs and nestlings are harder for Blue Jays and other predators to reach. Because multiple openings can also make a nest less secure, use only a well-tested design and protect the supporting tree or pole with an effective predator baffle.
A Nest Box for Brown Creepers
North America’s Brown Creeper normally tucks its nest behind a loose flap of bark or into a narrow crevice in the trunk of a mature tree. It may accept a nest box, but only when the structure closely imitates this unusual natural nesting site.
Commercial creeper boxes are therefore open along the side that faces the tree. When mounted flush against the trunk, the rough bark forms the rear wall of the nesting chamber. Choose a mature tree with a trunk at least 10 to 12 inches in diameter and deeply furrowed or peeling bark. Oaks, cottonwoods, mature maples and pines can all provide suitable surfaces.
Fasten the box firmly so that there are no large gaps between it and the bark. Check the attachment each year to make sure it remains secure and does not constrict the growing tree. Place the box in a quiet, shaded part of a wooded yard, preferably near other mature trees.
Brown Creepers are delightful birds to watch. They spiral upward along trunks while searching bark crevices for insects, spiders and their eggs, using their long, curved bills like tiny forceps. With luck, a well-positioned creeper box may also offer a discreet view of their nesting cycle. Avoid opening the inspection panel once nest construction or egg laying has begun.
Brown Creepers favor mature trees with rough, deeply cracked or peeling bark. This unusual open-backed box imitates the protected space behind a loose slab of bark.
The Open-Front Nest Box
In addition to conventional boxes with round entrance holes, there are open-front models intended for birds that naturally nest on ledges, shelves, shallow cavities and sheltered building surfaces. In the United States, these boxes are most likely to attract Eastern Phoebes, Say’s Phoebes, American Robins and, in some regions, Carolina Wrens.
Robins and Carolina Wrens generally prefer a box or nesting shelf hidden among dense native shrubs, beneath a porch roof or in another sheltered location with nearby cover. Eastern Phoebes often choose a more open site beneath eaves, decks and bridges, especially when the nest is protected from direct rain and intense afternoon sun.
Western gardeners may attract Say’s Phoebes with similar shelves attached to barns, sheds or other quiet structures. Both phoebe species frequently nest close to people, provided the site remains relatively undisturbed and offers an unobstructed flight path.
Several manufacturers sell broad, shallow nesting shelves designed specifically for robins and phoebes. Low-profile models are especially useful beneath bridges, culverts, porch roofs and other protected ledges near ponds, streams or drainage corridors. Mount them where cats, raccoons and snakes cannot easily reach the nest, and leave the old nest in place only until the breeding season has clearly ended. Clean the shelf before the following spring.
Nesting apartments
Purple Martins are among North America’s best-known colonial songbirds. They spend much of the day catching flying insects and, in many parts of the eastern United States, readily accept specially designed multi-compartment houses or hanging gourds.
A martin house is not simply a lawn ornament that can be installed and forgotten. It should stand in a broad open area, close enough to human activity to appeal to the birds but well away from trees and other obstacles. The structure must be easy to lower so that the compartments can be inspected, cleaned, and protected from predators and invasive birds.
Where the habitat and regional breeding range are suitable, one well-managed house can accommodate several nesting families. A poorly placed or neglected one, however, is far more likely to be occupied by House Sparrows or European Starlings. These introduced species compete aggressively for cavities and may destroy the eggs, nestlings, or adults of native birds.
Modern architecture for wrens
Small, energetic wrens often pass unnoticed as they explore shrubs, brush piles, porch corners, and woodland edges. Their rich songs usually reveal them before their brown plumage does. Depending on the region, a backyard may be visited by House Wrens, Carolina Wrens, or Bewick’s Wrens.
Instead of a decorative woven “nesting ball,” offer a durable wooden box designed for the species living in your area. A House Wren box normally has a 1-inch entrance and is mounted about 5–10 feet high near trees or tall shrubs, while Carolina and Bewick’s Wrens may accept more open, partially enclosed designs placed roughly 3–6 feet above the ground. The entrance should remain easy for the birds to approach rather than being buried deep inside dense foliage.
Use untreated wood, provide ventilation and drainage, and omit the perch—cavity-nesting birds do not need one, and it may help predators reach the entrance. Because male House Wrens sometimes fill several nearby cavities with incomplete “mock nests,” avoid clustering small boxes closely around active boxes intended for chickadees, bluebirds, or other native birds.
For medium-sized birds: woodpeckers and nuthatches
There is no universal “medium-bird” nest box. A White-breasted Nuthatch may use a compact box with a 1¼-inch entrance, whereas a Northern Flicker requires a much deeper structure with an entrance about 2½ inches across. Flicker boxes are generally mounted 6–12 feet high near open woodland, orchards, parks, or field edges and are packed with coarse wood chips so the birds can excavate their own nesting chamber. Nuthatch boxes belong in mature woodland or wooded residential areas where natural cavities are scarce.
Before building or purchasing a box, identify the native species you hope to attract and use a plan created specifically for it. Entrance diameter, interior depth, mounting height, habitat, spacing, and predator protection all matter. Whenever it can be done safely, preserving dead or dying trees is even more valuable, since woodpeckers excavate cavities that are later inherited by many other birds and small mammals.
The Northern Flicker is a familiar woodpecker of open woods, parks, and spacious yards. At a nest cavity it braces itself against the trunk with its stiff tail while delivering food to its young.
For larger birds: kestrels, barred owls, barn owls and mourning doves
Several medium-sized and large birds that normally nest in tree cavities will accept spacious nest boxes, but each species requires its own dimensions and placement.
American Kestrels prefer boxes overlooking open grassland, pastures, or broad fields, with an unobstructed approach to the entrance. In regions where they are native, Barred Owls use deep boxes placed in quiet, mature woodland. Near ponds, marshes, and slow-moving streams, a similarly proportioned box may instead attract a Wood Duck.
Barn Owls require a broader design resembling a large kestrel box. It should be installed inside or on a quiet barn, silo, or other structure overlooking open hunting habitat and away from busy roads. Even when these boxes are not used for nesting, they may provide winter shelter for birds such as Northern Flickers or Eastern Screech-Owls.
For Barred Owls and Wood Ducks
Installing large nest boxes in suitable parks, preserves, and wooded properties can replace some of the cavities lost when old or damaged trees are removed. A Barred Owl box should be mounted high in a mature tree within quiet woodland, with an open flight path and several inches of untreated wood chips on the floor.
Wood Duck boxes belong near wetlands and should be protected from raccoons, snakes, and other climbing predators with a properly fitted metal baffle. Keep large boxes well separated, avoid placing them beside heavily traveled roads, and inspect and clean them after the nesting season.
For the Barn Owl
A familiar bird of farms, ranches, and other open landscapes, the Barn Owl readily nests in human-made structures when suitable natural cavities are scarce. A large nest box can be installed inside a barn, silo, shed, or similar outbuilding, with its entrance opening directly outdoors; it may also be mounted on a sturdy freestanding post. Place it roughly 8 to 25 feet above the ground, overlooking grassland, pasture, marsh, or agricultural fields. A shallow layer of untreated wood shavings may be added, although the owls eventually create their own nesting substrate from shredded pellets.
Use a rear or side inspection door that can be opened safely, but avoid checking the box during the sensitive early stages of nesting. Clean it only when it is unoccupied. Most importantly, do not use rodenticides around owl habitat: Barn Owls feed largely on mice, rats, and voles and may be exposed to poisons through contaminated prey.
For the American Kestrel
North America’s smallest falcon is an especially welcome resident of open country. Unlike the European kestrel, the American Kestrel does not live principally on rodents: it feeds mostly on grasshoppers, beetles, dragonflies, and other invertebrates, while also taking voles, mice, small birds, reptiles, and amphibians. Providing a properly designed nest box can help where old trees, abandoned woodpecker holes, and traditional farm buildings have disappeared.
This large box substitutes for the hollow trees Barred Owls normally seek in mature woods and wooded parks. The birds are strictly nocturnal, so they are most often detected at dusk by their resonant, rhythmic hooting.
Bat Houses
Some bat house boxes (like the one shown in the picture above) are made up of a specialized mixture of wood shavings (75%), lime, cement, and other additives that make it possible to create box models in every conceivable shape.
Bats may be among the most misunderstood animals that visit our yards. They are not blind, they do not deliberately fly into people’s hair, and the overwhelming majority have no interest in humans. What they are is remarkable: bats are the only mammals capable of true, powered flight. In the United States, most species feed on insects, and their nightly activity contributes to healthy forests, wetlands, farms, and gardens.
Many North American bats use different shelters at different times of year. During summer, females of some species gather in warm maternity roosts where they give birth and raise their pups. As winter approaches, bats may migrate to milder regions or hibernate in caves, mines, rock crevices, hollow trees, and suitable parts of buildings. A standard backyard bat house is primarily a warm-season roost; except in areas with mild winters, it should not be expected to provide the stable conditions bats need for hibernation.
Bats in summer…
A bat house can provide useful summer shelter, especially where old trees, loose bark, natural cavities, or traditional building roosts have disappeared. It will not suit every bat: tree-roosting species such as hoary bats and eastern red bats usually shelter among foliage or beneath bark rather than inside artificial boxes. Colonial, crevice-roosting species—including big brown bats, little brown bats, and Yuma myotis within their respective ranges—are more likely to investigate a purpose-built bat house.
Begin with a genuine bat-house design rather than trying to convert a small birdhouse. The most useful models are tall, weather-tight maternity houses with at least four chambers, ventilation near the lower portion, and an open entrance along the bottom. The interior should be made from untreated material and have roughened or closely grooved surfaces that bats can grip. Narrow spaces imitate the cracks beneath loose bark: chambers about ¾ inch wide suit smaller species such as little brown bats and Yuma myotis, while big brown bats may use spaces between 1 and 1½ inches wide. A textured landing area beneath the entrance helps arriving bats climb into the roost.
Location matters just as much as construction. Mount the house on a building or sturdy pole, generally 10 to 16 feet above the ground, with an unobstructed flight path in front of and beneath the entrance. Avoid mounting it on a tree, where branches create shade, obstruct access, and give predators an easy approach. Bat Conservation International recommends leaving at least 12 feet of open space below the exit whenever possible.
The correct amount of sunlight depends on climate. In hot parts of the South and Southwest, morning sun, afternoon shade, good ventilation, and a light-colored exterior help reduce overheating. Cooler regions may require greater solar exposure and a somewhat darker finish. Installing two nearby houses with different orientations can give bats a choice of temperatures as weather conditions change. Properties with outdoor cats are poor locations because bats must drop from the house before taking flight and can be vulnerable near the ground.
Do not be discouraged when a new house remains empty. Bats may take several seasons—and occasionally as long as five years—to discover and accept an unfamiliar roost. Protecting mature trees and safely retaining dead or declining trees is generally more valuable than installing artificial shelters, so a bat house should supplement natural habitat rather than replace it.
Small, single-chamber boxes can heat and cool too rapidly. Tall, vented, multi-chamber houses provide a wider range of temperatures and are the better choice for most yards. During very hot weather, watch for bats crowding around the entrance, fanning their wings, flying in daylight, or pups falling from the house—possible signs of heat stress. Temporary shade may be needed, followed by improvements to the house or its location.
You’ll know them by their calls
The United States is home to about 47 bat species, and distinguishing them in flight is rarely easy. Size, silhouette, flight pattern, habitat, and range can offer clues, but darkness and rapid movement make visual identification uncertain. Echolocation provides another way to investigate. Bats emit high-frequency calls and listen for the echoes returning from insects and surrounding objects; most of these sounds are ultrasonic and cannot be heard unaided by people.
A handheld or smartphone-compatible bat detector can convert those calls into audible sound or record them as digital files and spectrograms. The frequency, duration, rhythm, and shape of a call may narrow the possibilities, while stored recordings can be examined later or shared with an experienced observer.
Treat automatic identifications cautiously, however. Several North American species produce calls with overlapping characteristics, and background noise, vegetation, distance, and hunting behavior can alter a recording. Detector software and identification apps are excellent for confirming that bats are active and suggesting likely species, but difficult recordings may require expert review before a species-level identification can be considered reliable.
Ultrasonic detectors convert sounds at frequencies inaudible to the human ear into audible sounds. Different species of bats can be identified using an ultrasonic detector because each species uses a different frequency, and the detector provides this information.
BAT HOUSES
Bottom-entry houses for poles or open structures
Many modern bat houses are open at the bottom. Guano falls directly to the ground, so little routine cleaning is required, although the house should still be checked for damage and cleaned only when it is unoccupied. The open base also lets bats drop into flight without having to crawl through a small entrance hole.
Despite the traditional image of a bat house hanging from a tree, trees are usually not the best mounting sites. Branches create obstacles, foliage produces too much shade, and trunks may give raccoons, snakes, and other predators easier access. In most yards, a sunny wall or a sturdy pole in an open area offers better conditions. The entrance should be at least 10 to 16 feet above the ground, with approximately 12 feet of unobstructed space beneath and in front of it.
The most useful designs contain several narrow chambers rather than one large empty space. Each chamber develops a slightly different temperature, allowing bats to move toward warmer or cooler areas as outdoor conditions change. This is especially valuable during spring and fall, when temperatures fluctuate sharply, and during summer, when females are raising pups.
Interior surfaces must be rough enough for bats to grip. Shallow horizontal grooves, closely spaced wooden baffles, or other durable textured surfaces work well; smooth plastic or polished wood does not. Removable panels may be helpful in research or professionally monitored installations, but homeowners should never open or disturb an occupied bat house. Any maintenance should wait until the bats have left for the season.
For walls and buildings
Wall-mounted nursery houses are especially useful for bat species that already roost in human-made structures. A building provides greater thermal stability than a tree or exposed pole, and a large wooden, brick, or concrete surface retains warmth after sunset. These conditions can make wall-mounted houses attractive to maternity colonies and other groups seeking a secure daytime refuge.
Choose a high, unobstructed section of wall where bats can approach and leave without passing through dense branches, wires, or outdoor furniture. Morning and midday sun are often beneficial, but the amount of solar exposure should match the local climate. Houses in cool northern regions generally need more sun, while those in the hottest parts of the South and Southwest may require protection from intense afternoon heat. Installing two houses with different exposures can provide a broader range of temperatures.
The box should be large enough to retain heat and should contain multiple narrow roosting spaces. Tiny, birdhouse-sized models and oversized single chambers are less likely to provide the stable range of temperatures bats need. The landing area and chamber walls should be deeply grooved or otherwise textured so that even young bats can climb easily. Open-bottom designs prevent most guano from accumulating inside, although the ground below may occasionally need to be cleaned.
Place the house away from bright security lights and keep cats indoors, particularly around dusk and dawn. A nearby pond, stream, wetland, woodland edge, or native garden can improve the surrounding habitat by supplying drinking water and night-flying insects. However, installing a box does not guarantee occupancy. Bats may take several years to discover and accept a new roost, especially when it is not replacing an established site.
Built-in bat roosts
Bat roosting blocks and “bat bricks” can be incorporated directly into the exterior walls of houses, apartment buildings, schools, and bridges. From the outside, they resemble ordinary masonry units with a narrow entrance near the base. Inside, they contain textured cavities where bats can cling and shelter.
Built-in roosts are most successful when included in the original architectural plans. They should be high above the ground, protected from rain, free of artificial lighting, and connected only to the outdoors—not to attics or occupied rooms. Materials inside the cavity should be durable, rough, and free from toxic wood treatments or exposed adhesives.
Before renovating, sealing, or demolishing a structure that may contain bats, arrange for an appropriate wildlife inspection. Exterior gaps must not simply be closed while bats are inside, because adults or flightless pups could become trapped. Exclusion work should follow state wildlife regulations and be planned with a qualified bat specialist, particularly when a maternity colony or protected species may be present.
BATS IN THE CITY? • Common building-roosting bats
The species found around homes and city buildings differ greatly by region. These are several bats commonly associated with human-made structures in parts of the United States:
| Common name | Scientific name |
|---|---|
| Big brown bat | Eptesicus fuscus |
| Little brown bat | Myotis lucifugus |
| Mexican free-tailed bat | Tadarida brasiliensis |
| Evening bat | Nycticeius humeralis |
| Yuma myotis | Myotis yumanensis |
Little brown bats commonly use warm attics and bat houses across northern portions of the continent; Mexican free-tailed bats form conspicuous colonies in buildings and beneath bridges in the South and West; evening bats are most widespread in the Southeast; and Yuma myotis frequently roosts near water in western buildings and bridges.
Shelter Designs for Flying Squirrels and Other Small Mammals
Wooded yards throughout North America are home to small mammals that need secure places to rest, raise young, and escape winter weather. Flying squirrels may use artificial nest boxes where natural tree hollows are scarce. At ground level, shrews and other small wildlife benefit more from sheltered piles of logs, branches, and fallen leaves than from enclosed “houses.”
Southern and northern flying squirrels sometimes occupy boxes originally intended for small cavity-nesting birds. These nocturnal animals are easily overlooked, even when they live close to homes. Southern flying squirrels occur across much of the eastern United States, while northern flying squirrels are associated mainly with northern forests and higher elevations. Both rely heavily on cavities in mature trees, including abandoned woodpecker holes, but they may readily accept a properly designed nest box.
A box used by chickadees or wrens during spring and summer may later provide shelter for a flying squirrel. During winter, several squirrels may share the same cavity, especially in colder parts of their range. They do not remain asleep for the entire season, however. They emerge periodically to forage and may stay inside for several days when storms or very low temperatures make travel difficult.
A suitable flying-squirrel box can be made from untreated, rough-sawn wood. The interior floor should measure approximately 4 to 10 inches square, with a total interior depth of about 7 inches. Make the entrance only 1¼ to 1½ inches across and position it high on the side nearest the tree trunk. Small drainage holes in the floor and ventilation openings near the bottom help keep the interior dry. Mount the box roughly 10 to 20 feet above the ground on a mature tree in a wooded or densely planted area. A few dry leaves may be placed inside, but avoid cloth, string, dryer lint, or other materials that could entangle an animal.
Do not open a box during freezing weather or while it may contain young. Instead, watch quietly from the ground around dusk and look for fresh nesting material or signs of activity near the entrance. Clean a box only when you are certain it is vacant. Wear gloves, avoid stirring up dust, and never sweep or vacuum dried droppings or nesting material; potentially contaminated debris should first be thoroughly dampened with disinfectant.
At ground level, short-tailed shrews and related species fill an ecological role somewhat comparable to that of hedgehogs in European gardens. These tiny, secretive insectivores move beneath vegetation and leaf litter in search of beetles, caterpillars, spiders, slugs, snails, and earthworms. They remain active throughout the year and may occasionally be heard rustling through leaves after dark.
Shrews rarely benefit from a miniature enclosed house. A better shelter is a low pile of natural woody material. Begin with several untreated logs or thick branches laid loosely on the ground. Add a second layer at right angles so that small passageways remain between them, then cover the structure with thinner branches. Allow fallen leaves to gather around the edges without completely blocking the openings.
Place this shelter in a quiet, well-drained corner beneath native shrubs or along the edge of a wooded area. Shade, protection from wind, and an undisturbed layer of leaves are more useful than direct winter sunlight. Keep the pile away from the house foundation, sheds, play areas, and other places where rodents would create a health or property problem. Do not add food, and avoid using rodenticides or broad-spectrum pesticides nearby. Brush piles, fallen logs, standing dead trees that pose no safety hazard, and dense native vegetation can provide year-round refuge for many small mammals, birds, reptiles, amphibians, and overwintering insects.
Shrews are valuable but strictly wild garden visitors. They normally avoid people, although any frightened wild mammal may bite. Do not pick one up or dismantle an occupied shelter to examine it. Wild mammals may also carry ticks, fleas, or disease-causing organisms, so keep pets away and contact a licensed wildlife rehabilitator when an animal appears injured or unable to escape.
For the Smallest Garden Residents
As lawns, roads, buildings, and heavily managed landscapes replace natural habitat, insects—like birds and bats—often struggle to find safe places to reproduce. A wildlife-friendly yard should provide nesting space for creatures of every size.
This type of shelter is intended primarily for solitary native bees and beneficial solitary wasps. The diameter and depth of each tunnel help determine which species will occupy it.
Many native bees and solitary wasps belong to the insect order Hymenoptera. Some excavate their own burrows, but many others depend on existing openings: abandoned beetle tunnels in dead wood, hollow plant stems, cracks in stone, or soft-centered canes they can enlarge themselves.
Providing these nesting resources does not necessarily mean constructing an elaborate “insect hotel.” Preserving natural features—bare soil, standing stems, old logs, snags, and brush piles—is usually the most effective approach. Natural sites spread nests throughout the landscape rather than concentrating them in one structure, which may reduce the buildup of parasites and disease. Small, well-managed artificial nests can supplement these features when natural cavities are scarce.
These insects reward us quickly. Native bees pollinate wildflowers, fruit trees, vegetables, and many other plants, while solitary hunting wasps gather caterpillars, aphids, beetle larvae, and other small prey for their young. Most solitary species are not aggressive around people because they do not have a large colony or honey supply to defend.
Bare Ground
About 70 percent of North America’s native bee species nest underground. The simplest way to welcome them is to leave several small areas of exposed or lightly vegetated soil in sunny, well-drained parts of the yard. These patches may be level or situated on gentle slopes and can include sandy soil, loam, or firm clay; different species prefer different textures and moisture conditions.
Avoid covering every open space with bark mulch, gravel, landscape fabric, or dense turf. Even a thin mulch layer can prevent tiny bees from reaching the soil. Once a nesting area is discovered, protect it from digging, heavy foot traffic, frequent irrigation, tilling, and pesticide treatments.
A patch containing dozens of entrance holes may look like a colony, but it is often an aggregation of solitary females. Each bee excavates and provisions her own tunnel, although many individuals may choose the same favorable bank or sunny patch.
Inside Natural Cavities
Other native bees nest above ground in preexisting holes. Dead trees and branches perforated by wood-boring beetles are especially valuable and should be retained wherever they do not create a safety hazard. Large carpenter bees (Xylocopa species) can excavate galleries in weathered wood, while mason bees, leafcutter bees, resin bees, and many solitary wasps generally occupy tunnels that already exist.
Standing stems provide another important nesting resource. Native species of raspberry and blackberry, elderberry, sumac, rose, goldenrod, sunflower, and bee balm may produce hollow or pith-filled stalks. Instead of cutting every perennial to the ground, leave stems standing through winter. In spring, trim some at different heights to expose their interiors, then allow them to remain undisturbed as long as possible. Small carpenter bees may excavate the soft pith, while other species use naturally hollow stems.
Once inside a tunnel, a female constructs a row of individual brood chambers. Mason bees separate the chambers with mud. Leafcutter bees (Megachile species) cut rounded pieces from living leaves and use them to line and divide the nest. Resin bees collect sticky plant resins, while some solitary wasps build partitions from mud, chewed vegetation, or other materials. Each chamber receives an egg and enough stored food for the developing larva.
Artificial nesting blocks can be useful, but they should be small, sheltered from rain, and designed so that the nesting materials can be replaced or opened for inspection. Smooth tunnels of several diameters—approximately 3/32 to 3/8 inch—will accommodate different species. Each tunnel must be closed at the back, and the shelter should receive morning sun without overheating during the afternoon. Permanent, oversized “bee hotels” filled with materials that cannot be cleaned may eventually harbor mites, mold, parasites, and pathogens.
This compact shelter contains bundles of hollow, untreated plant stems beneath an overhanging roof. Different tunnel diameters can attract several kinds of solitary bees and wasps. Mount the shelter firmly in a visible, rain-protected location, and replace used or damaged nesting materials regularly. A structure approximately 8 × 9 × 12 inches is large enough for most home gardens.
The eastern carpenter bee excavates nests in weathered dead wood and unpainted lumber. Adults that emerge in late summer often overwinter inside old tunnels. In spring, a female enlarges an existing passage or chews a new one, then divides it into a row of brood chambers. Each chamber contains a ball of pollen and nectar and is separated from the next by a partition of chewed wood.
WHERE DO BEES NEST?
Examples of nesting sites
Many bees use broadly available nesting places, while others depend on very particular materials or structures. Most native North American bees nest underground, but others occupy hollow stems, beetle tunnels, rock crevices, or abandoned animal burrows.
| Nesting substrate | Bee genera |
|---|---|
| Bare or lightly disturbed soil | Andrena, Halictus, Lasioglossum |
| Ground beneath sparse vegetation | Bombus |
| Vertical clay banks and earthen walls | Anthophora |
| Sandy banks and well-drained slopes | Colletes, Perdita |
| Pre-existing holes about ⅛–⅜ inch wide in dead wood, hollow stems, or properly maintained nesting blocks | Osmia, Megachile, Hoplitis, Heriades, Hylaeus, Ashmeadiella |
| Pith-filled stems of raspberry, blackberry, elderberry, sumac, and similar plants | Ceratina, Hylaeus |
| Solid dead wood or unpainted, weathered lumber | Xylocopa |
| Crevices in rocks, masonry, and other sheltered cavities | Anthidium, Hoplitis, Osmia |
| Abandoned rodent burrows, old bird nests, nest boxes, leaf litter, and spaces beneath sheds or grass clumps | Bombus |
| Exposed nests made with plant resin, pebbles, or bits of soil | Dianthidium |
| Drainage holes and other small cavities in garden structures | Megachile |
Native flowering plants are essential companions to nesting habitat—and are often more valuable than an insect hotel alone. Rattlesnake master (Eryngium yuccifolium), a North American member of the carrot family, provides pollen and nectar for bumble bees and many solitary bees.
NEST BOXES
The removable front panel allows brief inspections of the nesting tubes to see whether a solitary bee or wasp has moved in. Keep checks infrequent, avoid handling occupied tubes, and replace the panel promptly.
Artificial nests for solitary bees and wasps are now sold alongside birdhouses and bat houses. The simplest designs consist of untreated wooden blocks containing smooth, dead-end tunnels of several diameters. Bundles of hollow reeds, paper tubes, or pithy plant stems closed at one end can also be used. Because North American mason bees, leafcutter bees, and beneficial solitary wasps vary in size, a range of tunnel widths may attract several species.
Mount a small nesting unit firmly about 3 to 6 feet above the ground, where it receives morning sunlight but is sheltered from rain, strong wind, and intense afternoon heat. An east- or southeast-facing wall beneath a roof overhang is often suitable. Leave occupied nests outdoors through winter so the insects emerge in response to natural seasonal temperatures; bringing them into a heated building could cause them to emerge before flowers and food are available.
Decorative “insect hotels” may contain clay, bark, pinecones, straw, or other materials, and their crevices occasionally shelter lady beetles, lacewings, spiders, or other small animals. Their most dependable occupants, however, are cavity-nesting solitary bees and wasps. Large permanent hotels can concentrate mites, parasites, and disease, so removable paper liners, replaceable reeds, or blocks that open for cleaning are safer than deep holes drilled into wood that cannot be maintained. Plastic tubes should be avoided because they retain moisture.
Natural habitat is even more valuable: leave some hollow stems standing, retain safe pieces of dead wood, and provide patches of undisturbed, well-drained soil for the many native bees that nest underground. A few small, well-maintained nesting units are generally better than one enormous hotel crowded with hundreds of tunnels.
This tunnel is occupied by one of North America’s standout native pollinators: the blue orchard mason bee (Osmia lignaria). In an observation nest, you may see the mound of pollen and nectar placed in each cell to feed the developing larva. The cells nearest the entrance are generally the last ones completed and often contain males, which usually emerge before the females farther inside.
The United States is home to roughly 4,000 species of native bees, and most bear little resemblance to the defensive, colony-dwelling insects people commonly fear. The small mason bees, leafcutter bees, resin bees, and solitary wasps that occupy nesting blocks are generally docile. Because each female cares only for her own nest rather than defending a large colony, these insects rarely sting unless they are trapped or handled.
A second kind of artificial nest, though usually less attractive to insects than ordinary reeds or wooden tunnels, has tremendous educational value: the observation nest (below). Its nesting channels are covered by a removable opaque panel, with a transparent surface beneath. By briefly lifting the cover, you can follow the construction of brood cells, the growth of larvae, the formation of cocoons, and—eventually—the emergence of the adults without opening or destroying the nest.
The materials separating the cells often reveal who has moved in. Mud partitions suggest mason bees or potter wasps. Neatly cut circles of leaves point to leafcutter bees, while plant fibers may belong to carder bees. Resin, flower petals, pebbles, or pieces of grass provide additional clues. The provisions inside are equally informative: bees leave pollen and nectar, while solitary hunting wasps stock their cells with spiders, aphids, caterpillars, crickets, or katydids.
Occasionally, the nest may also attract tiny parasitoid wasps, beetles, mites, or other organisms associated with cavity nests. These visitors are part of the natural community, but heavy infestations can harm developing bees. Use nesting tunnels that can be opened, replaced, or cleaned rather than permanent drilled blocks, and replace soiled materials regularly to prevent the buildup of parasites and disease. Smaller nesting units distributed around the garden are generally safer than one enormous “insect hotel.”
BEES OR WASPS? — A ROOM FOR EACH
These are some of the North American insects most likely to occupy a properly designed tunnel nest. The exact species will vary with region, habitat, season, and tunnel size.
| Common cavity nesters | Cell or nest material | Food supplied to young | Approximate tunnel diameter |
|---|---|---|---|
| Yellow-faced bees (Hylaeus) | Cellophane-like glandular lining | Pollen and nectar | 3/32–3/16 in. (2.5–5 mm) |
| Orchard and mason bees (Osmia) | Mud; sometimes chewed leaves | Pollen and nectar | 3/16–3/8 in. (5–9.5 mm) |
| Small mason bees (Hoplitis, Ashmeadiella) | Mud, leaf pulp, petals, or small stones | Pollen and nectar | 1/8–1/4 in. (3–6 mm) |
| Leafcutter bees (Megachile) | Cut pieces of leaves or petals | Pollen and nectar | 3/16–5/16 in. (5–8 mm) |
| Resin bees (Heriades and some Megachile) | Plant resin, fibers, and grit | Pollen and nectar | 3/32–3/16 in. (2.5–5 mm) |
| Wool-carder bees (Anthidium) | Soft plant hairs, sometimes mixed with resin | Pollen and nectar | 3/16–5/16 in. (5–8 mm) |
| Spider-hunting wasps (Trypoxylon) | Mud partitions | Paralyzed spiders | 1/8–1/4 in. (3–6 mm) |
| Aphid-hunting wasps (Passaloecus, Psenulus) | Resin, plant fibers, or glandular secretions | Aphids | 3/32–3/16 in. (2.5–5 mm) |
| Grass-carrying wasps (Isodontia) | Dry grass and other plant fibers | Crickets or katydids | 1/4–3/8 in. (6–10 mm) |
| Mason and potter wasps (Ancistrocerus, Euodynerus) | Mud partitions | Caterpillars | 3/16–5/16 in. (5–8 mm) |
Providing several tunnel diameters—from about 5/64 to 3/8 inch—will accommodate a greater variety of local species. Tunnels should be smooth, closed at the back, deep enough for several brood cells, and sheltered from moisture. Allow wild insects to colonize them naturally rather than importing cocoons from distant regions.