Bird feeders drive some birds into decline

Feeding wild birds may seem like a great way to bring nature into your backyard, but birdfeeders may unintentionally harm types of birds that can't eat birdseed, a new study suggests.

The study found that stocking backyard bird feeders with bread and seeds caused the population of some species to explode at the expense of native species that don't eat bread and seeds, causing those species to decline.

While the research was conducted in New Zealand, other studies suggest the results are "definitely applicable" to other regions around the world, including Canada, said Josie Galbraith, lead author of the study in an interview withQuirks & Quarks that airs Saturday.

• Hear the full interview on Quirks & Quarks May 16 at noon on CBC Radio One

Galbraith, a PhD student in biological sciences at the University of Auckland, and her colleagues ran their experiment for 18 months in Auckland, New Zealand. Over the course of the study, theycomparedbird populations around 11 homes with bird feeders to those around 12 homes without bird feeders.

They found the feeders boosted populations of the European house sparrow and the spotted dove both introduced from overseas. The four most common native species, which don't eat seeds and bread,were unaffected. But populations of a small insect-eating native bird called the gray warbler were halved in areas with a bird feeder.

"We think what's happening is their territories are being taken over by hundreds of invasive birds and they're physically just being displaced," Galbraith said.

The results were published in a recent issue of Proceedings of the National Academy of Sciences.

• Summary of the paper

Galbraith expects that similarly in other parts of the world, bird feeders will benefit one or two species while displacing smaller or quieter native species.

She doesn't necessarily recommend that people get rid of their feeders, as she thinks they're an important way for city-dwellers to connect with nature.

But she suggests people think about ways to encourage many different bird species with the type of food they offer and by choosing plants carefully in order to create a bird-friendlygarden.