Crowding may encourage migration

Heading south Climate may limit the number of species the area can support

Migratory birds may be fleeing for reasons other than frigid temperatures when they fly south for the winter.

So says Veronique Boucher-Lalonde of the University of Ottawa, a re-searcher who studies species richness, which is the number of species that exist in a given place.

She wanted to know why populations of migratory birds around the world are so predictable.

In a recently published paper, Boucher-Lalonde surveyed hundreds of range maps of migratory birds, finding they experience a variety of conditions, which, in broad terms, show they have greater physiological tolerances than many may think.

“If what species like is just staying in the same sort of environmental conditions throughout the year, then they would be better off not migrating,” she said.

So while Canada geese enjoy summers in the country for which they are named before wintering in the mid and southern United States, others have a different climactic travel itinerary.

Boucher-Lalonde, who isn’t an ornithologist by trade, didn’t give names of individual species in her paper.

Instead, she was looking for trends emerging from the more than 600 species she studied.

She observed that many migratory birds will occupy different temperature ranges in different seasons with different resources and precipitation levels.

“It definitely refutes many hypothesis about species richness,” she said.

Boucher-Lalonde said climate influences migration, but it’s because of limits in the number of species that can be supported in a region.

“There are exceptions, of course, but in general the individual species, when they migrate, they migrate to a place that is very different than the place they come from, which suggest that the climate actually limits the number of species that can be there and not really which ones,” she said.

“Because you get a whole different assemblage of species when the climate changes.”

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