Wednesday, April 04, 2012

The Extinction of Vancouver's Crested Mynahs

"It's possible that, left alone for a few more years, Crested mynahs would have become better acclimatized to Vancouver's climate, might even have figured out a way to spread beyond the mountains and thus fulfill the USDA's worst fears. Sitting on a nest for a crucial extra hour or two a day is hardly a huge leap forward. A few years ago, two University of British Columbia (UBC) evolutionists, Craig Benkman and Anna Lindholm, conducted an experiment on crossbills, a type of seed-eating finch whose bills curve sharply at the tips and do not meet, like a pair of badly aligned nail scissors. The birds have adapted to opening a particular kind of hemlock cone; when Benkman and Lindholm clipped their beaks, the birds could forage open cones, but were unable to open tightly closed cones. As the beaks grew and became more crossed, the birds were able to open closed cones again. This suggested that beak alterations had occurred gradually in nature, and that the birds would have had to adapt in many subtle ways to take advantage of the changes. Citing the UBC experiments, Weiner posits that crossbills with slightly altered beaks would have needed to refine their instincts for cone hunting, learn to recognize new types of food, develop new muscles to operate their new beaks, and so on. These physical changes would eventually lead to social and reproductive changes (as females chose mates with well-adapted beaks), and before long the world would have a whole new species of crossbill. Given more time, something similar might have happened with Vancouver's Crested mynahs.

But it didn't. Starlings happened instead. As I watched, the two Crested mynahs left their perches on the light fixtures and flew to a nearby telephone cross-tree, obviously hoping to roost for the night. Within five minutes they were assailed by three starlings. One of the mynahs scooted along the beam, chasing two of the starlings off, but the starlings merely flew up onto a wire and then returned. Before long two more starlings arrived, and both mynahs moved grudgingly back to their light fixtures, perhaps to protect their nest, but it seemed more as though they had just given up, realized that there was nowhere else for them to go, that wherever they tried to roost they would be ousted by starlings. Not violently, not aggressively, just edged out by sheer force of numbers, made uncomfortable, unwanted, forced into retreat."

<< Home

Powered by Blogger

.post-title { display: none!important; }