Keeping House Sparrows out of birdhouses

House Sparrows were introduced to Brooklyn, New York, in 1851 and now live across North America except Alaska and the far north of Canada (Cornell Lab). They take over nest boxes meant for bluebirds, Tree Swallows, chickadees and other cavity nesters, destroying eggs and killing nestlings and adults (NestWatch). No bluebird-sized box is sparrow-proof (NestWatch, NABS, Sialis.org), so the work is a mix of box choice, placement, food and regular checks.

Legal status at a glance

This is a summary of what the federal sources and nest-box organizations say, not legal advice.

State and local rules can differ. The US Fish and Wildlife Service says "States and communities may protect nonnative, human-introduced species at their discretion." NABS says state and local laws vary and should be checked first, and that relocating House Sparrows is illegal in some states and only moves the problem. Your state wildlife agency is the place to ask (NestWatch).

Identify the bird and the nest

The bird. Cornell describes a chunky sparrow, 5.9–6.7 inches long, with a rounder head, shorter tail and stouter bill than most American sparrows. Males have a gray head, white cheeks, a black bib and a rufous neck. Females are plain buffy-brown with dingy gray-brown underparts and a back striped with buff, black and brown.

The nest and eggs. NABS asks monitors to be "absolutely certain" a nest is a House Sparrow's before removing anything. Compare:

Entrance-hole sizes

Hole size is a physical barrier, but it only helps below the size a bluebird needs. NestWatch says House Sparrows fit through holes as small as 1¼ inches; an Ellis Bird Farm fact sheet says a 1⅛-inch hole keeps them out, though some get through 1¼ inches. For starlings, NestWatch says holes of 1½ inches or smaller keep them out; Ellis Bird Farm gives 1 9⁄16 inches or smaller, and Sialis.org says a 1 9⁄16-inch hole "will also exclude almost all starlings."

Seven passive steps

1. Place boxes away from sparrow habitat: farm houses, feedlots, barns and old outbuildings (NABS), dense development and grain-rich farmland (NestWatch).
2. Change the menu nearby. NABS says to skip cheap mixed seed with milo, millet or cracked corn. NestWatch adds black-oil sunflower, suet, mealworms and ground-scattered seed to the list of foods that attract these birds, and says safflower, nyjer and nectar draw them less. See our seed-by-species chart.
3. Match the hole to the bird you want (figure above). Chickadee boxes are less vulnerable to non-native birds (NestWatch).
4. Keep holes plugged until nesting season so migrants can claim boxes first (NestWatch). NABS notes plugging over winter also keeps sparrows from roosting in and claiming the box, but blocks bluebirds from roosting there in cold winters.
5. Consider box design. NABS says sparrows may be more reluctant to use small-volume Gilbertson PVC boxes; NestWatch adds that no scientifically documented method keeps them out for good.
6. Add a sparrow spooker after the first native egg (NABS); Sialis.org says before incubation begins. Remove it as soon as the young fledge, and never put one on an active House Sparrow nest. Spookers do not deter House Wrens (Sialis.org).
7. Check every box at least weekly so a sparrow nest is caught early. NABS says removing House Sparrow nests and eggs once or twice a week keeps the young from fledging. Our bluebird trail steps cover monitoring visits.

If a House Sparrow starts a nest

NestWatch strongly encourages monitors not to let House Sparrows or starlings breed in their boxes, and NABS says "It is better to not put up a nestbox than to have one that fledges House Sparrows."

• Nest removal. NestWatch suggests removing nest material every few days for at least a week, and says this works best with a single backyard box, because displaced sparrows may take over an active bluebird or swallow nest elsewhere. NABS warns the male rebuilds quickly and attacks other birds.
• Other methods. NestWatch also describes egg oiling, replica eggs, trapping (traps checked hourly) and humane euthanasia; NABS covers in-box and ground traps. Read their full guidance and your state's rules before trying any of them.
• If you can't keep up, a 2007 New York State Bluebird Society advisory suggests taking the box down, or plugging the hole or removing the floor if you keep it as decoration.

What NestWatch's 2018 survey found

NestWatch surveyed nest-box monitors in 2018 and received 871 complete responses (Bailey and colleagues, 2020). 30.3% had seen a House Sparrow or starling take over a native bird's active nest that year. Takeover rates by native host were 35.3% for Northern Flicker (only 19 nests), 23.0% for American Kestrel, 16.5% for chickadees and 9.3% for bluebirds. 36.9% of respondents did not manage these species at all. The authors warn that removing nests and eggs "may actually increase nest site takeovers" if sparrows move to the nearest occupied box.

Terms

• HOSP: four-letter code for House Sparrow, used on Sialis.org.
• Usurp: to "take over an active nest, causing it to fail" (NestWatch).
• Passive vs active control: NABS's split between steps that make boxes less attractive and removing nests, eggs or birds.
• Sparrow spooker: mylar strips on a frame above the box roof that flutter near the entrance (Sialis.org).

Checklist

• Hole sized for the target species; boxes away from barns, feedlots and grain (NABS, NestWatch)
• No millet, milo or cracked corn near the boxes (NABS)
• Bird and nest identified before anything is removed (NABS)
• Spooker on after the first native egg, off at fledging (NABS, Sialis.org)
• Native nests, including House Wren nests, left alone (NestWatch)
• State and local rules checked (USFWS, NABS)

Sources

• Managing House Sparrows and European Starlings — NestWatch, Cornell Lab
• How Are People Managing Invasive Birds at Nest Boxes? (Robyn Bailey, 2020) — NestWatch
• What should I do if another bird interferes with a nest I'm watching? — NestWatch FAQ
• House Wren nest box — NestWatch
• Black-capped Chickadee nest box — NestWatch
• Tufted Titmouse nest box — NestWatch
• Tree Swallow nest box — NestWatch
• Service Publishes Final List of Non-Native Bird Species (March 15, 2005) — US Fish and Wildlife Service
• List of Bird Species to Which the Migratory Bird Treaty Act Does Not Apply (April 16, 2020) — Federal Register
• House Sparrow Control (fact sheet, rev. January 2018) — North American Bluebird Society, PDF hosted by the New York State Bluebird Society
• A House Sparrow Advisory (2007) — New York State Bluebird Society (PDF)
• Managing House Sparrows: Experiments — Sialis.org
• Sparrow Spookers: Designs and Instructions — Sialis.org
• Nest and egg identification — Sialis.org
• Nestbox specifications — Sialis.org
• House Sparrow Overview — All About Birds, Cornell Lab of Ornithology
• House Sparrow Identification — All About Birds
• House Sparrow Life History — All About Birds
• European Starling and House Sparrow Control (fact sheet, rev. 2009) — Ellis Bird Farm, PDF hosted by the Maine Department of Agriculture, Conservation and Forestry