Urban development is booming, and with 9.7 billion people expected to populate the world by 2050, it’s no wonder. But the human need to build is altering a more feathery and flighty world, according to researchers who are studying how urbanization and suburban sprawl affect native bird populations.
A new study in the journal PLoS One is among the latest to focus on this issue, and it reached a startling conclusion: Development is forcing some typically monogamous birds to “divorce” their mates, flee their once-forested homes and start over in a new landscape — a transition that can cause them to lose half their breeding years.
That finding grew out of a decade-long project led by University of Washington wildlife science professor John Marzluff, whose team monitored six species of songbirds in three landscapes of the Seattle area: forested preserves, already developed suburban neighborhoods and neighborhoods transitioning from forest to subdivision. They banded birds’ legs and mapped their travels, keeping tabs on nesting, mating and breakups.
“We’ve been studying this issue from many different angles over the years,” Marzluff said. “Basically what we’re trying to figure out is why the community of birds changed so much with urbanization.”
Two of the species — the Pacific wren and Swainson’s thrush — were dubbed “avoiders” because of their dependence on ground shrubs and brush and their shyness around humans, characteristics that make them unable to adapt well to urban encroachment and the landscaped lawns that come with it. They were divorcing one another at a consistent rate and leaving in search of more forested habitat, the researchers found. Four other species, considered “adapters,” went about their business next to their new human neighbors; some even thrived in their newly developed areas.
Other studies have found similar effects of city life on bird development and behavior. Researchers at Ludwig Maximilian University and the Max Planck Institute of Ornithology studied great tits — a bird scientists call a synanthrope, or a species that benefits from living in close proximity to humans — and found that they also appear to suffer reproductively, yet in a slightly different way. While great tits bred earlier in urban areas, their eggs were smaller and their nestlings weighed less than those born in the country.
Some initiatives, including the U.S. Fish & Wildlife Service’s Urban Bird Treaty, are aimed at conserving bird habitats within cities and reducing hazards to urban and suburban birds. Researchers said understanding how cityscapes influence birds is essential to protecting those that live among us.
