Extreme cold puts animals to the test

            The extreme cold of the past two weeks has Rhode Islanders avoiding the outdoors as best as they can and loading on extra layers when they must go outside. Which raises the question of how wildlife will fare during this unusually cold period.

            Local biologists agree that most species of wildlife that spend their winters in Rhode Island are well adapted to weather the cold. They have evolved numerous strategies to deal with the conditions, from hibernation and torpor to thick fur coats and layers of fat.

Birds, for instance, have developed a number of adaptations that enable them to survive the extreme cold. According to Scott McWilliams, a physiological ecologist at the University of

Rhode Island, ducks can stand on ice for hours at a time and swim around in the icy water without suffering frostbite in their feet thanks to a counter-current heat exchange system in their legs. The warm blood flowing down to their feet warms up the cold blood flowing back to their core, and the blood in their feet is so cold that the difference between their foot temperature and the ice ensures that they lose little heat through their feet.

Birds also huddle together to stay warm, fluff up their feathers to provide an insulating layer around them, and lower their body temperature to save energy.

But not all birds are prepared for the cold.

“Most sensible birds will migrate to warmer places, thereby avoiding having to contend with the cold,” McWilliams said. Some of those that stick around, however, “ are less well-insulated or otherwise poorly adapted to living in cold places." 

He points to the Carolina wren, a southern species that has expanded its range northward in recent decades. Southern New England is at the northern part of its range, and during extreme and extended cold spells in Rhode Island, many of the birds do not survive. That was the case during the winter of 2015, when the state had a record snowfall and the state’s Carolina wren population declined. When favorable weather returns, however, the wren population bounces back again until the next severe winter.

Cold-blooded creatures like reptiles and amphibians – animals that cannot regulate their own body temperature – are also well prepared for extreme cold. Wood frogs, for instance, have what some scientists call antifreeze in their blood that enables their tissues to freeze solid without harmful effects. In some winters, the frogs experience several freeze-thaw cycles.

Herpetologist Scott Buchanan said that adult painted turtles, snapping turtles, and spotted turtles are also extremely cold tolerant and will likely fare well. But some painted turtle hatchlings, which overwinter in their nest cavity, may die if the temperatures are extreme for an extended period of time.
"The invasive red-eared slider, on the other hand, is less tolerant of extreme cold - both the adults and hatchlings," Buchanan said. "Hatchlings, which also overwinter in the nest, are more vulnerable to these cold periods and would exhibit a greater rate of mortality than painteds or snappers.
"From a conservation perspective, this would be a good thing, as it would slow down the invasion," he added.

Wildlife that lives in the upper layer of the soil or in the grass at the surface may be particularly vulnerable to extreme cold, especially cold temperatures without a thick layer of snow to serve as insulation. David Gregg, director of the Rhode Island Natural History Survey, speculates that the dearth of leaves on the ground – thanks to two years of gypsy moth defoliation – may mean there will be less insulation for species that hibernate in the forest floor, such as box turtles and salamanders.

“Low temps and thin snow is also probably tough for small mammals like voles, which tunnel around in the grass,” Gregg said before this week’s blizzard. “Of course, that might make life easier for owls and hawks that need to be able to find voles.”

He also wonders about the impact of the cold weather on aquatic mammals when all of the local ponds are frozen solid. During the week before New Year’s, he twice observed a muskrat wander up from a nearby frozen river to scratch for food in his lawn.  And in the winter of 2015, a river otter emerged from the same frozen river to forage in his compost pit.

Charles Brown, a wildlife biologist with the Rhode Island Department of Environmental Management, isn’t worried about those aquatic mammals, however. He said the range of muskrats, river otters and beavers extends far to the north in Canada, where they likely experience much longer periods of extreme cold than they do in southern New England.

“So around here, they’re probably living the easy life,” he said.

Those animals typically gravitate to areas of moving water, like dams and spillways, during extreme cold, Brown said, and otters can even chew holes in the ice to gain access to pond water.

Brown is more concerned about how big brown bats will fare. He said that most bat species that spend time in Rhode Island migrate to caves to hibernate or travel south to warmer climates to avoid the winter conditions. Big brown bats are the only species that lives in the state all year. And even those should survive without much difficulty.

“We’ve had some pretty cold winters in the past, but rarely have I ever seen any evidence of bats dying from exposure,” he said.

The big picture, according to Gregg, is that the creatures that winter in the state do so for a reason, and there’s probably a logical reason for those that don’t survive the chill.

“I think that hard cold like this helps to hold back the northward expansion of southern species, like fire ants, kudzu and lizards,” he said. “The kind of animals and plants we think of as typical here are either helped or hurt in the appropriate ways by cold, so the net effect is good even though there are animals and plants that go up and others down.”

This article first appeared in EcoRI.org on January 7, 2018.