Urban avian rivalry: Birds fight it out for food and shelter in big cities

“We know these kinds of interactions are really important in nature and they determine which species has the best access to resources,” he said. “But we have no idea how these things relate to urban environments.”

Researchers looked at almost 300 bird species in 250 cities from Bangalore to Budapest to Bogota. The species were grouped into 142 closely related pairs such as the mountain chickadee and the black-capped chickadee, the house finch and the purple finch, the song sparrow and the swamp sparrow.

Biologists then looked at the behaviour of each species in the pair wherever their urban territories overlapped. Even when both species were well-adapted to city life, researchers found that the stronger species of the pair tended to let the weaker know that the town wasn’t big enough for the two of them.

“The larger size can often predict who’s going to win,” Martin said. “More muscle mass, larger weapons like bills or talons — all those things provide a benefit to larger species in a fight.”

The real surprise came when researchers realized that the law of the streets may not apply everywhere.

Dominant species seem to run off the subordinate pair mostly in economically developed cities. For the rich, dominants ruled.

Not so in developing cities.

“In those countries, we find species living alongside the dominant species in cities,” said Martin. “The competitive effects that we found for developed countries are completely missing.”

Why is that? Martin doesn’t know.

Perhaps it has something to do with how resources such as food are distributed in developed cities. Large, centralized food resources for birds — for example, managed waste disposal sites — may be easier for a flock of bigger birds to defend against a smaller rival.

That’s for future study. For now, Martin’s content with the new insight into how wildlife behaviour varies as it comes into human communities — research he calls vital as humanity becomes more and more urbanized.

“There’s been a lot of interest in our impacts on wildlife,” Martin said. “We’re seeing more and more evidence of actual evolution in organisms in response to urban environments.

“The public is interested as well. Those are the organisms they see everyday.”

— Follow @row1960 on Twitter

Bob Weber, The Canadian Press

by Canadian Press

Urban avian rivalry: Birds fight it out for food and shelter in big cities

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