A newly published study in the journal Ecology finds evidence that the wing shape of birds in North America has changed over the last 100 years as an adaptation to the loss of forest habitat.
Andre Desrochers from the Universite Laval looked at over 800 museum specimens of boreal and temperate forest songbirds. He found that over half of the species he examined demonstrated changes over time with boreal birds developing more pointed wings and temperate birds developing rounder wings. These results support the hypothesis that habitat isolation is spurring evolutionary changes in birds.
Boreal forests have suffered severe deforestation over the past century, and so Desrochers had predicted that increased distances between habitat patches would select for more pointed wings in birds. Pointed wings are associated with more energy-efficient sustained flight.
Conversely, temperate forests have undergone extensive afforestation (i.e. expansion of cover) over the past 100 years after an earlier period of forest loss. So Desrochers hypothesized that evolution would be spurring more rounded wings in these birds given that pointed wings can have higher energy costs for take off and foraging.
According to the results, 11 of the 21 studied species showed changes in wing shape over time with 10 of the changes consistent with those predicted by the hypothesis. As a control, the study also measured bill length and found little change over time.
Desrochers concedes that other factors could be at work - for example, the changes could be partly non-genetic effects of environmental stressors - but the Habitat Isolation Hypothesis gives the strongest explanation. Such a rapid species evolution in response to environmental change would be remarkable and has direct relevance to conservation. Desrochers writes,
"Birds’ ability to adapt rapidly to forest loss and fragmentation may mitigate, without necessarily preventing, the risk of regional extirpation of extinction. Further research should investigate the potential for rapid evolution in response to habitat fragmentation in other parts of the World, in particular the tropics, where recent decline in habitat area, as well as lack of dispersal ability in birds, are sometimes drastic."
--Reviewed by Rob Goldstein
Desrochers, A. (2010). Morphological response of songbirds to 100 years of landscape change in North America Ecology DOI: 10.1890/09-2202