If you have a birdhouse in your yard, your good intentions in attempting to provide birds with a place to nest should be applauded. However, many people don't realize that by allowing a birdhouse to stand unmanaged, they are indirectly harming the very birds the house was meant to benefit, by providing a breeding ground for the worst enemy of bluebirds - the House Sparrow.
|A Sparrow Spooker protects nestlings and eggs from House Sparrow attacks 24/7. It should be put up after the first bluebird egg is laid, and removed after the babies leave the box.
The once common bluebird underwent a dramatic decline during the 1900's. A major cause was the introduction of the House (English) Sparrow. The avian equivalent of pests like rats, gypsy moths and crabgrass, House Sparrow populations exploded. They are harmful to native species such as Bluebirds, Purple Martins, Chickadees, and Tree Swallows. (If you're not sure what a House Sparrow looks like, they can often be seen in the garden section of a Lowes/Home Depot, or around fast food restaurants.)
House Sparrows are persistent, aggressive and destructive predators. They may destroy eggs and nestlings; and kill adult birds caught inside the box, sometimes building their own nest on top of the corpse. House Sparrows will not only prevent native birds from nesting in your birdhouse, but they will also breed there. Soon House Sparrows take over all available boxes.
Bluebirds rely on pre-existing nest sites like nestboxes. To help native bird populations rebound, successful bluebird landlords take steps to keep House Sparrows and European starlings (another aggressive bird that was introduced) from breeding in any birdhouses on their property.
Because House Sparrows are smaller than bluebirds, they can get into
any box a bluebird can enter. There are a few styles of nestboxes not preferred by House Sparrows, including the Gilbertson. Fishing line placed strategically on a nestbox may make it less attractive to House Sparrows. A simple homemade device called a “Sparrow Spooker” with fluttering mylar strips brushing the roof top works wonders, and protects nestbox contents 24/7. It is installed after the first bluebird egg is laid (so it doesn’t scare off the bluebirds too), and removed after the babies fledge to encourage another brood and avoid House Sparrows getting accustomed to it. Instructions on how to make a Sparrow Spooker are available here: http://www.sialis.org/sparrowspooker.htm.
Because House Sparrows and starlings are not native, and are considered nuisance species, they are not protected by federal law. House Sparrow nests, eggs, young, and adults may be legally removed or destroyed. Of course you must first be absolutely sure that it is actually a House Sparrow. Generally only two “brown” birds use nestboxes – the other is the native House Wren, which is smaller, arrives in CT later in the year, and builds a nest made out of sticks. It is illegal to interfere with the nest of any native bird.
If you are not willing or are unable to control House Sparrows, consider taking the nestbox down altogether. If you want to leave the house up as a decoration, you can either plug the entrance holes, use a 1 1/8” hole reducer which will allow Chickadees or House Wrens to nest, use a "fake" painted hole on decorative boxes, or remove the birdhouse floor.
One person indiscriminately putting out bird seed can also radically change neighborhood wildlife. Do not feed birds bread, or seed that contains a lot of millet or cracked corn, as this attracts House Sparrows. Thistle, safflower, and black oil sunflower seeds are enjoyed by many native birds, but are not preferred by House Sparrows. Dumping food on the ground can also attract rats.
For more information on how to attract native birds or manage House Sparrows, see http://www.sialis.org. It is better to have no box at all than to allow House Sparrows to reproduce in one. Helping reduce the population of House Sparrows and starlings enables native birds to survive and thrive.