A proper birdhouse is important for attracting native species
September 13, 2011
If house sparrows overtake a swallow nest box or European starlings claim a house meant for purple martins, the problem might be in the housing provided by gardeners and homeowners.
The design flaws can allow aggressive, non-native birds to thrive and push native species into decline.
Some ready-made birdhouses may look cute, but might not be designed to keep the bullies of the bird world out.
Birds do not need perches, for example, but the features attract house sparrows and starlings.
The state Department of Fish and Wildlife recommends for design and construction of birdhouses to be species-specific.
The most important part is the entrance hole. If the hole is too small, the desired bird cannot enter. If the entrance is too big, undesirable wildlife — such as non-native sparrows and starlings, and uninvited squirrels — can get in and harm, evict or kill the intended bird.
What to know
Learn more about proper nesting boxes for native bird species in the state Department of Fish and Wildlife’s “Woodworking Projects for Backyard Wildlife” guide at http://wdfw.wa.gov/ living/projects.
Find comprehensive information on the Sialis website. For starling problems, go to www.sialis.org/starlingbio.htm and for house sparrow problems, go to www.sialis.org/hosp.htm. Learn how to create and manage tree swallow nest boxes at www.treeswallowprojects.com/index.html.
As a rule, house sparrows cannot enter a nest box if the entrance hole is less than 1 1/8 inches in diameter. Starlings cannot enter if the hole is less than 1 1/2 inches in diameter.
Birdhouses often need to be maintained on a yearly basis to stick to the specs. Patch or restore the entrance holes after squirrels or woodpeckers attempt to enlarge them.
If aggressive, non-native species persist, design alternatives exist.
A diamond-shaped entrance hole measuring no more than 7/8 of 1 inch deep and up to 3 1/2 inches wide should exclude house sparrows and starlings.
To accommodate the slightly bigger violet-green swallow, file down the area inside of the entry hole by just one-quarter of 1 inch.
The purple martin is a species in need of some suitable nest sites within Western Washington, because the species seems to be in decline. In fact, the purple martin is a candidate for state protective listing, in part because of competition from sparrows and starlings.
State Biologist Chris Anderson said although purple martins nest in colonies, “apartment complex”-style birdhouses can be a problem in urban areas with numerous starlings and house sparrows.
“A cluster of gourds drilled with holes seems to be much less preferred by starlings and house sparrows and the martins love them,” Anderson said.
Also, be more strategic in placing bird nest boxes.
Martins, like all swallows, feed on insects, mostly on the wing, and often over water where insects concentrate. Hanging a gourd collection over water makes the nesting spot much more enticing to martins and less inviting to sparrows and starlings.
Neither non-native species usually nests within 10 feet of the ground. Placing nest boxes 4 to 5 feet off the ground and in brushy areas should discourage house sparrows and starlings, and should be used by many native species, such as bluebirds to wrens.
However, nest boxes at the lower height can be vulnerable to predators, such as cats.
If push comes to shove, removing house sparrows or European starlings from nesting in a birdhouse is allowed under law. Because state and federal law do not protect the non-native species, it is legal to remove the birds’ nests and destroy their eggs. Nests may need to be removed five or six times before sparrows or starlings finally abandon the house.
Sometimes, the best thing to do in areas plagued by starlings or house sparrows is to let the birds win and not use bird nest boxes at all.