Nest Boxes for Native Birds

By Aline Cullen and Claudia Coleman, UC Master Gardeners

Natural habitat for birds has decreased primarily due to land development and natural disturbances.  Nest boxes can be beneficial for over 50 species of birds, both for local use and during migratory activity.

Benefits

• Nest boxes provide a safe environment for birds to raise their young, slowing the decline of songbird populations.
• There is a decreased need for pest control as birds will feed on grasshoppers, caterpillars, beetles, ants, psyllids. Predatory activities will extend to adjacent areas.  For example, Western Bluebirds forage within 50 yards of their nest.
• Decreased need for weed control as some birds have a voracious appetite for seeds.
• Birds can be visually striking, melodious, and entertaining. Their presence also provides the opportunity to observe subtleties of their behavior.

Birdhouse Guidelines

The choice of a nest box is not random, as birds will choose a site appropriate for raising their young.

• Entry holes: Birds will judge the nest box primarily based on the size of the entry hole. It should be large enough for entry but small enough to keep out predators.
• Height: The preferred height of nest box from the ground varies by bird species. Small birds find homes mounted on a post 8-10 feet off ground acceptable.  Woodpeckers prefer houses that replicate their preferred environment- 15-20 feet from ground, mounted on a tree.
• Placement: Location of the nest box will vary by bird species. The box should be securely fastened to withstand winds. A house facing an open field is preferred by bluebirds.  Openings should face away from prevailing winds, in partial shade, with free access to fly in from a nearby roosting tree used for monitoring of predators.
• Discourage climbing predators: Place baffles beneath the nest box to impede predators such as cats, snakes, squirrels and raccoons.  Perches on the nest box are not necessary and can be used by predators.
• Paired nest boxes: Bluebirds are territorial but may tolerate other bird species.   They will not nest in a nest box within 100 feet of another bluebird.  Paired nest boxes 15-25 feet apart will encourage bluebirds and tree swallows to nest.
• Specific requirements for many bird species can be found at NestWatch, The Cornell Lab of Ornithology, see references.

Birdhouse Construction

• The Basics: Nest box should have thick walls, a sloped roof with 1-2-inch overhang, ¼ inch holes in sides and bottom for ventilation/drainage and one removable or hinged panel to allow for cleaning.
• Material: Non-treated wood (not metal).
• Paint: non-toxic paint for exterior in natural colors. Bright colors can encourage predators. Interior should not be painted.
• Interior: rough surface and grooves beneath exit hole for young birds.
• Size: appropriate for size of bird, too large of a nest box is not attractive to birds.
• Timing: Nest box should be mounted or cleaned and aired out by late January. Clean out nesting material and clear ventilation holes at least once a year.
• Other: Perches are not necessary and can be used by predators.

How to discourage exotic invasive bird species from competing with native birds:

Invasive species such as European starling and house sparrow compete with native birds for natural nesting cavities and nest boxes.  They kill bluebird adults, their young, and destroy eggs.

• Excluding European Starling: Entry hole of 1 ½ inches will deter, as will smaller nest boxes. An oval entry hole of 1 3/8” x 2 1/4” will keep out smaller starlings.
• Excluding House sparrows: A bluebird size entry hole of 1 ¼ inch will not deter them.  Mount nest box on a pole less than 5 feet.  If they occupy a nest box, clean out nesting material every few days and they will leave.  Only use this method if no other bluebird occupied nest box is nearby as the ejected house sparrows may kill birds in adjacent nest boxes.
• Food: Do not scatter bird food on ground; avoid mealworms and suet. Instead use thistle or safflower.  Do not feed birds with small seeds like millet, cracked corn and milo preferred by house sparrows; or black oil sunflower seeds favored by starlings.  Feeders with short perches are not attractive to these species.

Other Habitat Considerations

• Water: Bluebirds are attracted to dripping water and shallow water, less than 2” deep.
• Proximity to fruiting trees and shrubs. Retain snags, trees and perches. Maintain open grassy fields.
• Avoid pesticide and herbicide usage to prevent loss of natural bird food sources.

References

“Western Bluebirds.”  All About Birds. The Cornell Lab of Ornithology. https://www.allaboutbirds.org/guide/Western_Bluebird/lifehistory.

"All About Birdhouses.” Nestwatch. The Cornell Lab of Ornithology. http://nestwatch.org/learn/all-about-birdhouses/.

NABS Factsheet: Getting Started with Bluebirds. PDF.  North American Bluebird Society. http://nabluebirdsociety.org/PDF/FAQ/NABS%20factsheet%20-%20Getting%20Started%20-%2024May12%20DRAFT.pdf.

Heaton, Long, Ingels and Hoffman. Songbird, Bat and Owl Boxes. UC ANR. Publication. 2008. ANRCatalog - Songbird, Bat and Owl Boxes - ANR Catalog