Nesting Boxes
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| Bluebirds "house hunting" at a trail Airlie Garden in New Hanover County |
For many gardeners and birdwatchers in the Northern Hemisphere, "Spring" is an exciting time after a long period of cold, grey days. This means the beginning of the growing season, the return of birdsong, and for some areas warmer temperatures. In the Carolinas "Spring" is fairly early with Mid-February being equivalent to March in the Northeast, Midwest, or much of Europe (Spain and Portugal are more like us except with a different climate) and the British Isles. For birds, this is the beginning of breeding or nesting season. After the grey, rainy, and cool winter of 2020-2021 (though it was not frigid), I was excited when I heard Brown Thrashers and Cardinals singing outside my townhome, or when Bluebirds and Carolina Chickadees were moving into birdhouses at my mother's house, I grew up in.
We talked about nesting season at the beginning of this blog last April but most species were already raising young by this point. This time, I am going to explain how to provide supplemental nest sites for garden birds, and which types of birds may move into birdhouses or other nesting boxes. While this article came out a little late as most resident birds scout for nest sites in the Autumn or Winter, it should still be valuable for new and experienced gardeners and birdwatchers. It is never too late to install birdhouses, or add features to landscapes, and many of our breeding species have yet to arrive.
Supplemental Nest Sites
Nesting boxes, shelves, and other manmade structures intended for breeding birds will be collectively called supplemental nest sites for the purpose of this article. While enclosed birdhouses are the most common type of nest structure, there are dozens of other structures that are used for birds. These can range from repurposed teapots, pails, or terracotta pots for wrens, chickadees (or their counterparts in Europe), to specalized nest sites like wood or stone towers for swifts, multiroom birdhouses for Purple Martins, and yes, even pigeon cotes. These structures provide alternative nest sites for birds in urbanized, agricultural, or otherwise developed areas, or can boost natural sites in forests, woodlands, and meadows.
Hole nesting (or cavity nesting) birds are the most common adopters of supplemental nest structures and are also the most likely to use traditional birdhouses. Many of these birds are losing nesting habitat as dead trees and limbs (deadwood) are removed, stumps and debris are cleared, and modern building designs eliminate nooks or crannies that birds used for nesting. Putting in one or multiple nest sites can make a big difference and could bring new species of birds to your garden or encourage visitors to set up residence.
Types of Nest Sites
Nesting Boxes or Birdhouses: Enclosed structures that contain a hole, slot, or other opening for birds to enter. This is the most common type of nest structure
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| A standard birdhouse in front garden |
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| Roofed nesting shelf on tree. These are favorites for thrushes, certain martin/swallow species, doves, flycatchers and starlings |
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| Gourd someone gave me as a child, this gourd lasted 8 years (placed in sheltered area) and hosted wrens, flycatchers, and chickadees. |
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| Whicker finch basket (intended for aviary/cage birds) with Carolina Wren nest in it |
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| Wood Duck box at Greenfield Lake |
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| This dead tree at Greenfield hosted Common Starlings, Red Bellied Woodpeckers, and Crested Flycatchers at the same time. Birdhouses are a substitute for natural cavities. |
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| Wren's nest at our townhome in 2019, nested in a portable greenhouse near doorway |
Nesting Boxes in the Carolinas
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| Bluebird house along a trail at the New Hanover County Arboretum |
History: In the Carolinas, nesting boxes and some of the other artificial nest sites from the list above are popular with garden birds. A standard nest box or enclosed containers will work for most gardens and will host many of the smaller species of birds in our region. Nesting boxes have been used in North America for at least a century although birdhouses became common after the 1960s when people became aware of declining songbird species. The Eastern Bluebird was the target species for most birdhouse projects as these thrushes were declining rapidly and almost went extinct by the 1960s. There were many factors in the declines of birds including pesticides such as DDT, the loss of forest habitats, woodlands, and in rural areas in the East, hedgerows and copses, domestic cats or dogs, as well as nonnative species like House Sparrows. The birdhouses helped bluebirds and other songbirds to find alternate nest sites when cavity trees, overturned stumps, or old outbuildings became scarce. Today, the Eastern Bluebird is a common species in the Carolinas and along with the Carolina Chickadee, is one of the most likely species to use birdhouses. The Bluebird Trail Movement of the 1960s-70s caught on in the Southern and Midwestern United States and led to birdhouses being installed and maintained in cemeteries, parks, pastures, and even urban trails. Along with Eastern Bluebirds, these trails also host Tree Swallows, chickadees, House Wrens, and Crested Flycatchers.
Purple Martins: Purple Martins are another species of bird that people often host in their gardens or near farmland, for many years. This species of martin is unique to the Americas and has become accustomed to using gourds put out by Native American cultures. Purple Martins later became popular with farmers for insect control and as a hobby. By the Mid-20th Century, gourds were replaced or supplemented by specially built multiroom nest boxes that are often called "Condos" "Apartments", or "Martin Houses". Purple Martins are hole nesters and like its globally distributed relative the Barn Swallow (or simply Swallow), and its Old-World counterpart the House Martin, the birds are virtually dependent on humans for nesting. Martin houses are commonplace in the Carolinas, especially near the sea. Purple Martin houses are often seen in front or back gardens in Wilmington, Myrtle Beach, Beaufort, New Bern NC, Charleston SC, and other coastal cities as well as near farms, rural homesites, and in public parks. Purple Martins bring many benefits including controlling pest insects (though they rarely eat mosquitoes), and can bring hours of joy. However, unlike other birds, Purple Martin colonies have to be actively maintained to be successful and only nest in urban, suburban, or populated rural areas with open space and water. I often compare Purple Martins to Honeybees in that they can run into a host of problems such as parasites, predators, and other issues, rely mostly on human structures, and are always in colonies.
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| My only Purple Martin visit, circa 2011. This Martin House was too close to treetops to be attractive. It was later taken down after House Sparrows started trying to use it. |
Wood Ducks: Wood Ducks are the only native waterfowl species (and the only duck) that nests in most of the Carolinas, as Canada Geese are "technically nonnative" and only arrived in our region in the 1960s-70s. Mallards occasionally breed inland or in the Northeast of Carolina (like Outer Banks or other locations in NE-NC). Wood Ducks are another species like the Eastern Bluebird that we almost lost from overhunting, habitat loss, and pesticides. This colorful species of duck nests only in tree hollows, holes (made by Common Flickers or Pileated Woodpeckers), or other sheltered sites, sometimes 15m (50ft) above the ground. With the loss of large trees and deadwood for timber salvage, safety purposes, or from major hurricanes, these ducks had no place to go. The ducks also compete with Grey Squirrels, Red Bellied Woodpeckers, Raccoons, and to a lesser extent the nonnative Common Starling. Large wooden or plastic (rarely metal) boxes with round or oval holes were installed near creeks, rivers, and ponds in the Carolinas and other regions to provide nest sites for Wood Ducks. These boxes were successful and helped to stabalize or even reverse declines in ducks in our area. Aside from Wood Ducks, the Hooded Merganser also uses nest boxes and has nested in our area on occasion.
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| Wood Ducks are common in our area but often overlooked, they could nest near any body of water if a proper box is installed. |
Other Projects: There are a number of other projects relating to artificial nest sites for birds in our area. Many of these projects are for specific species of birds that have declined rapidly over the past 30-50 years, or are in need of special nest sites. The Barn Owl is a globally distributed species of owl that hunts almost exclusively rats and mice. These birds are declining rapidly in North America and Europe due to the loss or modification of old barns, silos, stone buildings (like churches), or natural tree holes, as well as rodentcides, and competition with more powerful species (such as the Great Horned Owl or Eurasian Eagle Owl). In North Carolina, many organizations are installing specially built boxes in rural areas for Barn Owls, although I think these will work in cities as well as Barn Owls are still seen in urban settings as well. There are also nest boxes built for the tiny but rarely seen Screech Owl, and even the larger Barred Owl. Organizations and conservation groups have also installed platforms atop towers (about 3-6m or 10-20ft high) for Ospreys, Bald Eagles, Red Tailed Hawks, or Great Horned Owls, while the endangered Red Cockaded Woodpecker has been helped with nesting boxes drilled into living pine trees to replace nest trees lost in storms or to logging.
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| An Osprey/Bald Eagle tower in Maine, this one has an active Osprey Nest on it. |
Species that use Nesting Boxes in the Carolinas
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| A Carolina Chickadee nest, the most common birdhouse user in the Carolinas |
- Wood Duck
- Hooded Merganser
- Eastern Screech Owl
- Saw-Whet Owl (Appalachia)
- Barn Owl (Occasionally)
- Kestrel
- Red Headed Woodpecker
- Red Bellied Woodpecker
- Downy Woodpecker (Occasionally)
- Hairy Woodpecker (Occasionally)
- Pileated Woodpecker
- Common Flicker
- Crested Flycatcher
- Tree Swallow
- Carolina Chickadee
- Tufted Titmouse
- White Breasted Nuthatch
- Red Breasted Nuthatch (Appalachia)
- Brown Headed Nuthatch
- Carolina Wren (Occasionally)
- House Wren
- Winter Wren (Appalachia)
- Eastern Bluebird
- Common Starling
- Protonotary Warbler
- House Sparrow
Shelf/Ledge Nesters
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| Doves such as this Mourning Dove, and the related the Rock Dove, Collared Dove or even the diminutive Ground Dove may accept mounted nesting shelves or wire baskets in trees. |
- Rock Dove
- Mourning Dove
- Collared Dove/Ringed Turtle Dove
- Barn Swallow
- Crested Flycatcher
- Eastern Kingbird
- Eastern Phoebe (Appalachia)
- Carolina Wren
- American Robin
- Common Starling
- House Finch
Nest Box Guide
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| An example of a standard bluebird box floor is approximately 10x10cm (4x4in). Inside are four Eastern Bluebird eggs |
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| Brown Headed Nuthatches also use nest boxes frequently. They will nest next to chickadees or bluebirds if the boxes are paired. |
Eastern Bluebird: 3cm or 1.25" diameter hole, box 10x10cm (4x4"). Height: 1-3m (3-10ft) above ground.
Place boxes in open or semi-open areas such as lawns, parkland, pastures, cemeteries, or low flowerbeds. May also use pinelands or open woodland.
Carolina Chickadee: 2-3cm (0.75-1.25") diameter hole, box 10x10cm (4x4"). Height: 1-2m (3-6ft) above ground.
Place boxes either in semi-open, or lightly wooded areas, will also nest near dwellings and in busy parks.
Tufted Titmouse: 3-3.8cm (1.25-1.5") diameter hole, box 10x10cm (4x4"). Height: 2-4.5m (6-15ft) above ground.
Place in hardwood forest or near large shade trees like oaks, may also nest in wooded gardens. Uncommon birdhouse user
Place in hardwood forest or pinewoods, may also nest in back gardens with large trees.
Brown Headed and Red Breasted Nuthatch: 2.5cm (1") diameter hole, box 10x10cm (4x4"). Height 1-4.5m (3-15ft) above ground.
Place near pines or in mixed woodlands, will also move into post mounted boxes in open neighborhoods and parks. Prefers boxes filled with sawdust or woodchips
House Wren: 2-2.5cm (0.75-1"), diameter hole, also likes slot-shaped holes, box 10x10cm (4x4"). Height above ground, less than 2m (<6ft) above ground.
Place in semi-open areas near shrubbery, hedges, or woodlands, readily nests in gardens and near dwellings.
Carolina Wren: 3-5cm (1.25-2") diameter hole, box 10x10cm (4x4"). Height less than 3m (<10ft) above ground.
Place in forests, near hedges, or in wooded parks, also uses shaded gardens. Uncommon birdhouse user but often uses open sided boxes, gourds, and wicker baskets.
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| Carolina Wrens use birdhouses on rare occasions but like gourds, baskets, or your mailbox. These colorful birds nest in wooded areas or gardens with established plantings. |
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| The smaller House Wren is one of the quickest birds to accept a birdhouse. These birds nest throughout the Carolinas and are expanding towards the coast. |
Install in wooded swamps, along creeks or perhaps near a garden pond in a wooded garden.
Tree Swallow: 3cm (1.25") diameter hole, box 10x10cm (4x4"). Height 2-3m (6-10ft) above ground.
Place in open area such as pasture, front lawn, cemetery, park, or near a wetland, prefers being near water. Pair up houses to accommodate both swallows and bluebirds as they can nest next to each other
Crested Flycatcher: 5cm (2") diameter hole, or a slot shaped opening, box 10x10 or 15x15 (4x4 or 6x6") box. An owl, starling, or flicker box may also be used. Height. 3-4.5m (10-15ft) above ground is preferred, mount boxes on tree.
Place in forested area, edge of field, parkland, or in back garden. Flycatchers also use gourds and swinging boxes.
Common Starling: 5-6cm (2-2.5") diameter hole or slot shaped hole, box at least 15x15cm (6x6") in size. Height at least 3m (10ft) above ground on tree, structure, or post.
Place boxes in wooded areas, or in back gardens, will also nest near dwellings. Starlings often use nesting shelves on buildings.
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| Starlings can take over larger nest boxes or tree holes, but unlike House Sparrows, they are solitary nesters, breed only once per year, while sparrows may nest up to six times in a season. |
House Sparrow: Will use any box with a hole larger than 3.8cm (1.5") in diameter and females may even squeeze into 3cm (1.25") holes. Generally uses boxes higher than 2m (6ft) above ground.
Sparrows almost always nest near human dwellings, farmland, or livestock, rarely in open grassland or wooded areas.
Place near large trees or in woodlands, parks, or the back garden and fill with sawdust.
Hairy Woodpeckers use boxes on rare occasions, while Red Bellied Woodpeckers often use boxes (even without sawdust)
Red Headed Woodpecker: 4.4-5cm (1.75-2") diameter hole, box size either 10x10 or 15x15cm (4x4 or 6x6"). May also use a starling, owl, or flicker sized box. Place at least 3m (10ft) above ground. This woodpecker nests mostly in pinelands, open countryside, or pastures with scattered trees and may use suburban gardens.
Downy Woodpecker: 3.8cm (1.5") diameter hole, box size 10x10cm (4x4"). Height, at least 2m (6ft) above ground on tree trunk.
Place in forestland, woodland edges, or wooded parks. An uncommon nest box user but may roost in bluebird houses during the winter. Fill with sawdust or woodchips
Common Flicker: 6-7.5cm (2.5-3") diameter hole, box size is at least 15x15cm (6x6"), there are specially built Flicker Boxes or plans available. Height, at least 3m (10ft) above ground on tree trunk or post.
Place in pastures, open woodlands, pinelands, or in other open areas with scattered trees, including suburban areas and parks. Fill with sawdust to simulate excavation.
Pileated Woodpecker: Needs at least 15cm (6") diameter hole and a large box. It is best to repurpose a Wood Duck box by filling it with woodchips.
Height, greater than 3m (10ft) above ground on tree trunk. Place on the edge of woodlands, riparian corridors, or in the back garden, especially near large pines or hardwoods. Fill with sawdust or woodchips to simulate excavation.
Wood Duck/Merganser: Use a specialized hole about 15cm (6") in diameter and a large box. Wood Duck box plans and constructs are widely available. Place at least 2m (6ft) above water or ground, most boxes are about 3m (10ft) off ground.
Place anywhere within a safe distance from a pond or creek with no roads, fences or other obstructions.
Kestrel: Needs a 10cm (4") diameter hole and a box that is 15x15cm (6x6"), or repurpose an owl box. Height, at least 3m (10ft) above ground on post or tree.
Place in the open countryside, any field, meadow, or even a large cemetery or schoolyard could work for this falcon. Not likely to nest in wooded or urbanized areas.
Screech Owl: Hole size is at least 10cm (4") in diameter, preferably larger, although this species has gotten into smaller holes. Box size is 15x15cm (6x6"). Install at least 3m or 10ft above ground.
Place in any type of forest or woodland near water, a small clearing, or trail. May use a wooded park or large homesite as well.
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| Screech Owl at bird show, aside from this owl the Barn Owl and the more common Barred Owl may use large nest boxes. In Appalachia the Saw Whet Owl is also a hole nester. |
Providing Nest Sites
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| Parkland and cemeteries are good spots for public nest box trails. This stand of Longleaf Pines hosts Eastern Bluebirds, Brown Headed Nuthatches, and Red Headed Woodpeckers. |
Birdhouses are among the easiest ways to attract nesting birds to your garden although it does not replace providing natural habitat through landscaping. There are 12-13 species of birds that will use nest boxes in a garden setting with others on the lists above being possible tenants if you have the right habitat, live within their breeding range, provide the correct structure. As far as non-enclosed nest sites, the number could be higher as many birds are adapting to urban areas. For example, many open nesting birds in Europe or North America may adopt open sided boxes or shelves placed on buildings if there are no trees or natural ledges. Additionally, I have seen songbirds and Mourning Doves adopt wire frames, baskets, or other objects placed in shrubs or trees to build their nests atop. Nesting boxes can be installed almost anywhere and are readily available in stores, online, or can be built at home with basic woodworking skills. For this article, I will focus mainly on enclosed nest boxes, nesting shelves, and other containers as these are the most likely structures to be adopted. Purple Martins, and speciality projects are a subject for another article.
Choosing Nest Boxes: Today, there are a myriad of birdhouse designs available in stores or as plans. However, not all birdhouses are suitable for birds and some may even be hazardous if they include toxic paints, have poor ventilation, or come apart easily. In general, you should purchase only birdhouses that meet standard dimensions and are made of sturdy materials with proper ventilation. There are many plans and guidelines online and in books, though I recommend the website Sialis for plans, and tips on monitoring bluebirds and other hole nesting species. This website also has information about specific species, how to deal with invasives such as House Sparrows, and fun activities for children and families. A number of books including The Bluebird Monitor's Guide by Cynthia Berger, and the Stokes Bluebird Book (and Purple Martin Book) are also good resources for beginners and experts. Today, many retailers, hardware stores, garden centers, and almost any local store that sells bird stuff (wild birds not shops selling stuff for pigeons, parrots, or pet birds) carry Bluebird Houses and Wren/Chickadee Boxes.
General Design Guidelines for Birdhouses
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| Most stores carry standard birdhouses, these are examples of wren or chickadee boxes. Decorative boxes are fine as long as they are practical and safe for the birds. |
- Boxes should be constructed of untreated wood, or another material that is sturdy, and nontoxic
- Hole should range from 1.9-3.8cm (0.75-1.5") in diameter which is suitable for most species in the Carolinas. Larger holes are needed for Crested Flycatchers, Starlings, or most Woodpeckers.
- Note: Holes larger than 3.8cm/1.5" can allow House Sparrows in while 5cm/2" holes are enough for Starlings to enter, so keep boxes for wrens, chickadees, bluebirds, and swallows smaller than this to avoid problems.
- No perch should be added to the box as most birds can perch/cling, and a ledge will only make it easier predators to get in
- Box size for most birds is 10x10cm (4x4") although birds larger than Bluebirds need larger boxes.
- All boxes should have ventilation holes, drainage slots and overhanging roofs and be sturdy enough to survive storms
- Stay away from decorative boxes (i.e. ones that look like mansions, lighthouses, or brightly colored) as these are impractical and will be ignored. Other designs may even trap nestlings or will not hold up to the elements. Feeder birdhouse combos also do not work as the traffic from visitors will deter nesting.
- Also avoid Balsa or easy DIY kits as these boxes are likely to fall apart in a season
- If you paint or coat a box, do so only on the exterior with nontoxic (or less toxic) paint and allow to dry before installing. Stick with natural or light colors
- A standard Bluebird House, and Wren/Chickadee Box will work for most species with a 3.2cm/1.25" hole being ideal for everything from the tiny Carolina Chickadee or House Wren to birds up to the size of Eastern Bluebirds, while House Sparrows are mostly excluded from entering
- Always install metal flashing on birdhouses as woodpeckers, tree squirrels, mice, and chipmunks will enlarge cavities to move in, or eat the eggs and young.
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| A newly placed birdhouse in our back garden in 2011. Most domestic gardens are already home to chickadees, House or Carolina Wrens, bluebirds, and two or three woodpecker species. |
Placement: Most birdhouses are placed between 1-3m (3-10ft) above the ground, although some birds such as starlings, flickers, or the Pileated Woodpecker prefer boxes higher than this. Boxes or gourds placed lower than this are easy targets for cats, raccoons, foxes, and other predators even though chickadees and wrens are known to nest close to the ground or in burrows. In general most birdhouses should be placed in a relatively open area on a post to allow a line of sight. Tree mounted boxes also work although a squirrel, raccoon, or cat could ambush the box from a limb, and as trees grow in size, the box could get destroyed or knocked off. Hanging boxes are used by a handful of species including House/Winter Wrens, chickadees, and flycatchers (and the Purple Martin), but are ignored by others and may be susceptible to storms. Well placed swing boxes or gourds may be less vulnerable to mammalian predators or snakes, while House Sparrows and Starlings do not like them. All hanging boxes and gourds should be firmly secured to a branch, structure, or mounting structure with metal wiring, or a hook and inspected seasonally.
Orientation: Many experts, books, and websites suggest that birdhouses should be placed facing away from the prevailing winds or direct sunlight. In our area, this is often East or Southeast. However, in my experience, I found the direction not to matter as much as I have birdhouses that face in all directions (north, south etc) that successfully host bluebirds, chickadees, or wrens, and seen even boxes in direct sun or deep shade being used. However, I will say that boxes should not face oncoming winds (usually southwest in the Carolina) as rain may blow right into the hole, even if there is an overhang, likewise, north facing boxes may allow cold air to blow in the hole during a late spring cold snap. All boxes should face away from shrubbery, wooded areas, or buildings as birds need a clear flight path and vegetation or objects could easily hide a cat or raccoon.
Habitat: Birdhouses can be placed in virtually any habitat although I would not recommend doing birdhouses on beachfront property (nor would many birds use boxes in windy areas). In general, the habitat in your neighborhood or property does not matter that much as there are always birds that will move in if the box is placed in a suitable location. Bluebirds and Tree Swallows like more open spaces such as lawns, low flowerbeds, pastures, or areas with scattered trees. Titmice, Crested Flycatchers, and most Woodpeckers prefer more wooded environments like stands of trees, parks or gardens with old-growth trees, with is just about any place in Wilmington, or Raleigh NC. Chickadees, and House Wrens will nest anywhere including right on a patio, in an urban courtyard, or the edge of a pasture. In most gardens in our area, a birdhouse (or multiple birdhouses) can host chickadees, bluebirds, wrens, and nuthatches without any modifications. However, some birds such as Kestrels and Barn Owls need vast open areas, while the Screech Owl or in Appalachia Winter Wren only nests in forest interiors and are not likely to turn up in a birdhouse in an ordinary garden in the suburbs or city. Purple Martins also have strict requirements that are unique including open space around their colony (no overhanging trees), pastures, fields (including schoolyards and sporting fields) or water nearby Most interestingly, Purple Martins will only nest in close proximity to humans and will ignore a box or gourd cluster in a prairie or open field unless there are structures nearby. There is no garden I can think of that cannot host some kind of nest box, my lakeside townhome in Wilmington even has a wren box and makeshift nest boxes for the Carolina Wrens and Chickadees that live in our dooryard/garden.
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| The metal square around the box (flashing) prevents woodpeckers, squirrels, rats, or other animals from enlarging the holes of nest boxes. |
Protection: Birdhouses can be protected from predators through various means, although this is not always necessary. Baffles or other devices installed on poles can defeat squirrels, raccoons, opossums, and even rat snakes, although a box that is low to the ground can still be accessed by these animals. I do not have baffles on any of my birdhouses but had many successful broods despite my old neighborhood having plenty of outdoor/feral cats, raccoons, snakes, Red/Grey Foxes, and even Coyotes. I planted Carolina and Rugosa Rose under many of my birdhouses (or allowed Smilax and Blackberries to become established) which seemed to keep cats, snakes, and raccoons away without deterring bluebirds, chickadees, and even a pair of Brown Headed Nuthatches. The rose trick may not be a good idea if you have House Wrens and want to host other species as they are right at home in brambles or thickets. Other means of protection include metal flashing as I mentioned above, the use of hole extensions (known as Predator Guards), and durable materials. In the end, no nest box is completely predator proof and an animal will find a way to get in if there is a flaw. Avian predators such as hawks, owls, crows, and the Boat Tailed Grackle raid birdhouses on rare occasions (more so Martin Houses) although Red Headed and Red Bellied Woodpeckers pose more of a threat to hole nesters but can be blocked with guards or metal flashing. Except for Brown Rats, and the Coyote or Red Fox (in NC at least) all of the animals that may raid nests are native and part of the ecosystem. Prevention and proper placement is the best way to keep predators and nest thieves from getting the young.
Maintenance: With the exception of Purple Martins and possibly Chimney Swifts, most birds that use supplemental nest sites do not need any maintenance or care. Most books and websites about hosting birds in nest boxes do recommend or even urge people to monitor their birds regularly, remove pests such as blowflies or mites (using nontoxic means), and even manage undesirable species. While I encourage nest box monitoring and nest maintenance, it is not necessary for the birds' survival and a well-placed birdhouse with protection from predators should be enough for common species to be successful. Nest box monitoring, and pest control are all covered extensively in Stokes publications about Birdhouses, Martins, or Bluebirds, as well as on the Sialis.org website and is beyond the scope of this article. However, all birdhouse managers should clean out nest boxes between uses or at the end of the season, tighten screws or mounts, and replace boxes when they begin to decay. I also encourage people to use preventive measures to protect birds such as installing baffles or predator guards on low or vulnerable birdhouses, planting thorny plants (like roses) under birdhouses to deter cats or raccoons, and to put wire mesh or purpose built blowfly platforms so insects fall out of the nest. Old nest material should not be reused as it often contains droppings, uneaten food, insect parasites, and possibly dead birds or eggs. Discard the material in the garbage, or bury it. I am not sure about composting old nest materials because of the possibly of contaminants such as plastics (which many birds love to use) and persistent diseases.
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| House Sparrows are a nonnative and invasive bird that can take over birdhouses and even destroy nests or trap and kill the adults. (More info on Sialis.org) |
Nonnative Birds: Nonnative birds such as House Sparrows should not be encouraged and according to the Migratory Bird Treaty Act of 1918, nonnative and invasive bird species are not protected by Federal Law in the US. Nests and eggs of House Sparrows can be removed without penalty but be aware of local and state laws, and ethical views. The best way to take care of House Sparrows is to prevent them from using the birdhouse in the first place (by using holes smaller than 1.5" or 3.8cm), placing boxes away from grain silos, buildings, or hedges, or by using hanging birdhouses instead. Starlings are rarely a problem as they prefer larger holes, are always nest solitarily (House Sparrows may form colonies that number into the hundreds), and in our area, nest very early in the year (often February through April). A few native birds such as House Wrens, Red Bellied Woodpeckers, and even the beloved bluebird may also cause problems as well, especially with smaller or more vulnerable species. I have read reports of House Wrens destroying the nests of other birds, and personally seen bluebirds destroy nuthatch or chickadee nests. While this is disheartening, this is a part of nature and all of these birds (except the House Sparrows) are native and are part of the ecosystem. The best solution I have for this is to install multiple birdhouses (I had 5 at my mother's residence) or use birdhouses with smaller holes for chickadees, and Brown Headed or Red Breasted Nuthatches. For House Wrens, the best defense is to put bluebird or swallow boxes away from hedgerows, underbrush, or homes, while placing boxes for woodland species (such as the larger Carolina Wren or smaller Winter Wren) deep in forests. House Wrens do not like open fields, and also stay on the edges of woodlands. Sialis has an entire section just on dealing with nonnative birds and how to prevent other nest box problems.
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| This box for wrens is located on the patio of a back garden in Etowah NC. It was used by House Wrens, chickadees, and other birds despite being near the back door. |
Human Activities: Nest boxes should be placed in a quiet and relatively undisturbed area of your garden although this is not always possible in urban settings or on working agricultural areas. Nearly all of the common nest box species are tolerant of human activities. Bluebirds, chickadees, wrens, and nuthatches are as tolerant of people as House Sparrows are in city centers, while even the more timid species such as Crested Flycatchers or even the Pileated Woodpecker will warm up to people. In general, I would place birdhouses away from places you may host family gatherings, allow children or pets to play, or near driveways, garages, or the front door. While high traffic areas may not disturb the birds, it can bring the attention of opportunistic animals, delay birds trying to feed young or can lead to curious guests disrupting the nest cycle. Birdhouses can be placed in the back garden aways from outdoor areas, or in the front garden as long as the area around it is not along a busy street or sidewalk. I have one birdhouse in the front garden of my mother's place that hosted bluebirds, and chickadees for years despite overlooking a street and sidewalk and being just meters from the front door (with a Coral Honeysuckle bush behind it). At my townhome, Carolina Wrens and Chickadees readily nest in people's dooryards despite the business of an urban apartment complex next to a popular park with weekly lawn service, maintenance crews, and air conditioner units cutting on and off. With all of this considered, urban and suburban birds are quite resilient and are not disturbed by the day-to-day activities of the modern world. Just keep backyard parties, free running dogs, and children's activities away from the bird garden, and don't spray your garden with pesticides during the nesting cycle.
Other Considerations
Birdhouses and other nesting structures are a good fit in most gardens and normal human activities rarely disturb garden birds. However, there are a few more things to consider when providing nesting sites for birds. First off, all birds need their privacy when they are breeding. Try to install birdhouses, gourds, and or plant shrubs away from birdfeeders, bird tables, or popular water features. The coming and going of birds at a feeder will preclude a birdhouse that is too close from ever seeing any birds, as few species (aside from House Sparrows and Mockingbirds) will be happy next to an area busy with birds, squirrels, and those that come to feeders after hours.
Second, birdhouses should be spaced out for the same reason. While a small urban garden can host 3-5 birdhouses or nest sites provided they are placed in different areas and habitats, having too many boxes (I have seen pictures of yards with dozens of decorative boxes), will only encourage House Sparrows or House Wrens to proliferate, making it difficult to host any other species. I recommend placing one or two houses in a front garden, several in different areas of the back, or some on the side. Having several boxes ensures different species gets a chance to nest, and can add insurance should one of the boxes get taken over by a paper wasp or hornet colony, become the home of a mouse, or a House Wren fill a box with sticks. Some birdhouses such as Bluebird Houses can be paired to with the second box being used by Tree Swallows, or chickadee/Brown Headed Nuthatch.
Third, consider using things other than birdhouses to supplement nest sites. Gourds, whicker finch nests, repurposed pots, or containers, and hanging planters may be used by other species of birds. For example our primary wren species the Carolina Wren rarely uses traditional birdhouses but is quick to move into a terracotta pot, teapot, hanging ferns, door wreath or a spare mailbox. Chickadees and titmice will also use just about anything they can get their bodies into, while a Crested Flycatcher or Starling may take a nesting shelf just below the roofline of a house it is in the right habitat. Your garden could host most of the common cavity nesters in one season as many of the birds come at different times, and use microhabitats.
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