Forest Fragmentation Favors Pointed Wings
Many temperate hardwood forests in the Northeast suffered severe deforestation in the 19th century, which was followed by restoration in the 20th century. In contrast, the boreal forests farther north were subject to extensive clear cutting in the 20th century, causing fragmentation of the once intact forest.
Forest fragmentation may impose new selective pressures on forest birds. Dispersal and daily movements may be increased by miles of additional flights each year. Birds with pointed wings would be more favored. Pointed winged birds have higher mobility and more energy-efficient sustained flight. However, a reduction in forest fragmentation should favor more rounded wings given the higher energy costs of flight take-off and foraging with pointed wings, especially for birds that forage close to the ground or in thick understory.
So reasoned André Desrochers, a biologist at Université Laval in Québec. He decided to investigate how changes in forest fragmentation might have affected birds in the past. He examined over 850 bird specimens of 21 eastern songbird species in museums that were collected from 1900 to 2008.
As Desrochers expected songbirds from the more mature temperate forests evolved rounder wings, while those in the more recently fragmented boreal forests shifted towards more pointed wings. Resident boreal birds had wings that had become more pointed than migrant birds.
Perhaps the birds’ ability to rapidly adapt to forest fragmentation may help them from becoming extinct in some regions, says Desrochers. Further research is needed in the tropics where recent forest fragmentation coupled with resident tropical birds lack of dispersal ability can be drastic.
Source: Desrochers, A. 2010. Morphological response of songbirds to 100 years of landscape change in North America. Ecology. DOI: 10.1890/09-2202.