Stanley Breeden
North America's two kinds of flying squirrels are hooking up to create strange new hybrids, evidence that global warming is forcing the species out on a limb.
Northern and southern species that have been distinct for tens of thousands of years are now producing odd-looking offspring, says Colin Garroway, a biologist at Trent University in Peterborough, Ont., the lead author of a paper in the journal Global Change Biology that describes the mingling of the airborne rodents.
The cartoon character Rocky the Flying Squirrel was probably a northerner, Mr. Garroway speculated this week. Rocky is grey, and always with a moose (Bullwinkle). He is American, but there are pockets of northerners in the United States.
Rocky's white-bellied cousins, the southerners, have roots in hardwood forests. They are smaller, eat nuts and nest exclusively in the cavities of trees.
Both northerners and southerners can launch themselves from trees and soar through the air for 50 metres or more. When flying squirrels spread their arms and legs, flaps of loose skin attached to their wrists and ankles stretch into membranes that act like sails.
But northerners are bigger and have longer tails, and their belly fur is a mix of grey and white. They build nests and dine on the fungus that grows on softwood trees. It is likely that they descended from populations that found refuge in pockets of boreal forest when ice covered much of North America.
Population surveys have found that because of milder winters, the southern species, formally known as Glaucomys volans, is enjoying a population boom and moving north into territory traditionally occupied exclusively by the northern Glaucomys sabrinus.
The new paper shows that the two species are mating and producing hybrid offspring. "We were trapping funny-looking squirrels with mismatched hair and body features," says Mr. Garroway, a doctoral student who collaborated with his supervisor, Jeff Bowman, researchers at the Ontario Ministry of Natural Resources, and scientists in Alberta, Toronto and Pennsylvania.
Northern flying squirrels are about the size of a chipmunk and southern ones are roughly half as big. Some of the oddball squirrels are mid-sized with patches of white fur on their bellies.
This could be natural variation, so genetic testing was the only way to be sure that they were a mix of the two. Mr. Garroway collected hair from 271 flying squirrels - northerners, southerners and a few that looked like a cross between the two. Genetic testing showed that 11 of the animals were a 50-50 genetic mix of the two species and that the mingling was likely a recent phenomenon.
His is the first paper in a scientific journal on the melding of two species because of climate change, Mr. Garroway says. DNA tests showed that a bear shot in the Arctic in 2006 was grizzly-polar bear hybrid, although experts said the pizzly or grolar bear, as it was dubbed by the locals, was a rarity that may have nothing to do with climate change.
The conquest of the southern flying squirrels, on the other hand, appears to be linked to warmer winters. They advanced as far as Temagami in Northern Ontario by 2004. Then they retreated, before venturing north to Algonquin Park again last summer.
"It is a bit jittery, but it is happening," Mr. Garroway says.