Forest birds' wings get makeover, courtesy of evolutionary processes: logging, recovery may play role in the degree of pointiness.

When trees fall in the forest, unheard or not, they may reshape birds' wings.

As logging whittled away at Canada's vast boreal forest during the past century, bird species that frequent mature woodlands developed somewhat pointier wing tips, Andre Desrochers of the Center for Forest Research at Laval University in Quebec City reported August 13. During the same period, forests expanded in New England. Maturewoodland species there trended toward rounder wing tips.

Previous work has found that wing shape is highly heritable, Desrochers said, and he thinks rapid evolution is the most straightforward explanation for his new findings.

Sharper points on wings typically prove more efficient than blunter shapes during sustained flight, Desrochers said. But those points also have a cost. On tight maneuvers threading through 3-D mazes of branches, pointy wings lose out to rounder ones.

Several other studies have noted wingshape differences within the same species if some populations migrate and some don't. House finches in the eastern United States that follow the seasons, for example, tend toward sharper wings than western, couch-potato house finches.

Desrochers said he began to wonder whether human activities that leave forests in fragments might influence wings the same way migratory lifestyles do.

Logging in the conifer forest that once blanketed most of Canada means that birds now fly farther than their ancestors did to find prime territories and mates. Filling the gaping mouths of chicks in tattered forests also means longer commutes, and all the extra flying might change the balance of trade-offs for wing shape.

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To see if a hundred years of landscape change mattered, Desrochers measured wings of 851 specimens from 21 species offorest birds. Mature-woodland species showed the clearest change in pointiness regardless of body size, Desrochers said. During the past century, their long wing feathers, or primary feathers, gained about 2.23 millimeters on average.

Desrochers also included more southerly species on his list, such as the scarlet tanager and hooded warbler. During the past century, the landscape of New England, previously deforested, rebounded into green woodland again. And here, Desrochers found a trend toward rounder wing tips. The eight mature-woodland species he studied typically had lost, on average, some 2.37 millimeters off those long primary feathers.

"Birds are not like sitting ducks," said Desrochers. Species respond to the extent that they can when they face new challenges.

"It's surprising that there's so much change so fast" said ornithologist David Winkler of Cornell University. He noted that the study doesn't explicitly address whether the wing changes are genetic.

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