Impact of invasive bird species monitored by Lab of Ornithology network

By Allison Wells

Scientists at the Cornell Lab of Ornithology are asking the public to help monitor the impact on native birds of invasive species, such as the house sparrow, by participating in a citizen-science project called The Birdhouse Network (TBN).

In the mid-1800s, the little brown house sparrows were introduced into the United States from Europe to alleviate homesickness for the Old World and because they were believed to control insect pests. Since then, these adaptable birds have made themselves quite comfortable here -- spreading their wings across all of North America in vast numbers, according to TBN project leader Tina Phillips. She says surging populations of house sparrows have resulted in fierce competition with native birds for nesting sites.

According to 2003 data collected by TBN, house sparrows account for 43 percent of all competitor species (species that take over nest boxes intended for native birds). And although most nest-box (or bird-house) enthusiasts discourage nesting by house sparrows, the birds still comprise 10 percent of all reported nesting attempts when at least one egg is laid.

What effect is this having on North America's bluebirds, swallows and other native cavity-nesting species? "We don't know," said Phillips. "There are no long-term studies showing the effect of competition between house sparrows and our native cavity-nesters. This is one reason why we're asking everyone across the continent to become part of our nest-box monitoring project. The only way to get answers is to get data, which are provided most effectively by people who monitor nest boxes."

TBN participants monitor activity inside nest boxes and keep track of data such as egg-laying dates, numbers of eggs and nestlings, and fledging dates. The participants send their observations to researchers at the Cornell Lab of Ornithology, where the data are combined with observations from across North America, to determine the annual nesting success of cavity-nesting birds.

Competition with non-native species, such as house sparrows, as well as pesticide use and habitat loss resulted in a serious decline in bluebird populations in the middle of the last century. Today bluebird populations are rebounding thanks to bird enthusiasts who provide nest boxes in their yards, fields and neighborhoods. Phillips points out, however, that simply putting up nest boxes isn't enough. In order to ensure the long-term future of native cavity-nesters, nest-box owners need to monitor and report what's going on inside their boxes. Only then will scientists have a true picture of the current status and factors influencing breeding success of native cavity-nesting species.

One thing is known for sure: In head-to-head competition, house sparrows readily out-compete native species for nesting sites by evicting other nesting birds, destroying their eggs, killing nestlings and sometimes even killing the incubating female. Adding to the competition is the fact that once a male house sparrow establishes a territory, he remains there year-round and starts defending that territory early in the season, often preventing later-arriving species, such as bluebirds and swallows, from nesting.

House sparrows also are prolific breeders, raising up to four broods per season (compared with just one or two for bluebirds), each brood averaging four to five eggs. They are expert nest builders and rebuild nests at a rapid rate. For these reasons, TBN is collecting data for a new Nest-Box Competitor Study examining the effect of nest-box competition from invasive species on native cavity-nesting birds. Participants collect information about the competitor species using the nest box, the type of interference, if any, by monitors and the final outcome of the nesting attempt.

So far, the project has received more than 41,000 nesting records for more than 40 cavity-nesting species. Information, however, is still greatly needed for the Nest-Box Competitor Study.

Serious birders, beginners, families, classrooms, youth groups -- everyone is invited to become part of TBN. A registration fee of $15 ($12 for lab members) helps offset the cost of running the project. Participants receive a packet that includes a full-color poster of cavity-nesting birds, access to private and public cavity-nesting listservs, an annual subscription to the lab's quarterly newsletter "BirdScope," and access to an online database where participants can submit, organize, share and store their nest-box observations. People can sign up by calling the lab toll-free at (800) 843-2473; outside the United States at (607) 254-2473; or by visiting TBN's Web site at http://www.birds.cornell.edu/birdhouse.