Songbirds change to cope with deforestation

by Rich Heffern

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Eastern North American songbirds are a very adaptable bunch, says a scientist who discovered some remarkable changes in their wing shapes over the past century.

A close look at museum collections of 851 songbird specimens belonging to 21 species shows that most of the birds evolved wings that are more pointed after their forests were disrupted by logging. Others in re-forested areas evolved less-pointed wings. The drive to procreate forced the changes in wing shape.

More pointed wings can help birds who are long-distance commuters fly more efficiently. Rounded wings however, are better off over short distances.

"I've been studying the effects of (forest) fragmentation," said Andre Desrochers of Quebec's University Laval and the Laboratory of Ornithology at Cornell University. "Roads, rivers, clearcuts and other gaps can break up songbird habitats.

"To me, it becomes apparent that fragmentation is really a big problem" he added. "If you (as a songbird) are in a fragmented habitat, you have more chance of being without a mate."

To see if forest changes were causing evolutinary shifts in birds' bodies, Desrochers carefully measured museum species collected from 1900 to 2008. What he found supported the idea that birds adapted quickly to forest changes. His results were published in the latest issue of the journal Ecology.

Desrochers theorizes that the reason for the wing changes is that as forests are broken up, it gets harder for songbirds to find mates. Selective pressure forces birds to travel farther - from forest fragment to forest fagment - in order to find their true love. Birds that can do this better tend to succeed in mating and pass on their more efficient mate-searching traits - in this case more pointed wings - to their offspring.

Once the forests re-grow, however, there is no selective pressure for those pointy wings. In fact, there may even be a greater need for the birds to develop shorter wings for more maneuverability.

Birds are being bred for different wing shapes in the same way a dog, rabbit, or other domestic animal is deliberately bred by humans for a particular desired trait or set of traits.

"The pattern is clearly clear cut", agreed Michael Brooke, curator of ornithology at the Cambridge University Museum of Zoology. "Few people would have guessed that this result would come from museum collections. This study depended on 100 years of acquisition."

One of the lessons from the study, says Desrochers, is that species are not static. "The assumption that species do not respond adaptively to rapid environmental change caused by humands is frequent and probably wrong in many cases, and several authors have warned that this may lead to species mismanagements," he concluded.

All the specimens Desrochers studied were from the Cornell University Museum of Vertebrates and the Canadian Museum of Nature. The collections covered the period from 1900 to 2008 and included such birds as the Eastern meadowlark, field sparrow, mourning warbler, scarlet tanager, hooded warbler, pine warbler, and boreal chickadee.

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