Hibernating Animals Suffer Dangerous Wakeup Calls Due to Warming

Officialgroundhog handler Ben Hughes holds Punxsutawney Phil after the spinyhibernator made his prediction of an early spring in Punxsutawney,Pennsylvania, on February 2, 2007.
Animals around the worldmight benefit from a longer winter, scientists say. Global warming isdisrupting many hibernation schedules, sometimes with deadlyconsequences.
Photograph by Jason Cohn/Reuters
Scott Norris
forNational Geographic News
February 2, 2007
Punxsutawney Phil—the groundhog of Groundhog Dayfame—emerged from his stump-shaped shelter this morning and didn‘tsee his shadow, traditionally signaling an early spring.
Sun-worshipping humans might welcome the news, but forgroundhogs and other hibernating animals, a longer winter could be a blessing.
A recent trend toward increasingly mild winters is disrupting normalhibernation patterns for many high-latitude and high-elevationspecies—and in some cases it may be a matter of life or death.
From marmots in the Rocky Mountains to bears in the Moscow Zoo,animals are spending less time napping. The change may be placing somespecies fatally out of synch with their environment.
When animals hibernate they‘re able to conserve the energy stored intheir fat during periods when food is scarce. So when they areabnormally active, they risk using up their stored energy before theycan replace it.
(See"Polar Bears Suffering as Arctic Summers Come Earlier, Study Finds" [September 21, 2006].)
Born Too Late
In England the warmest winter on record has left young hedgehogs at risk.
Probably confused by changing climate patterns, hedgehog mothersgave birth relatively late in the year. As a result, their pups did nothave time to put on sufficient weight to hibernate successfully and arenow starving.
And dormice, small rodents known for their six-month-longsiestas, now hibernate five weeks less than they did two decades ago,Italian scientists report.
For some species a long winter sleep may already be a thing of the past.
Researchers in Spain recently announced that European brownbears have stopped hibernating altogether in the northern CantabrianMountains.
Mothers with young cubs have remained active in recent winters, becausewarmer temperatures and decreased snowfall have made food resourcessuch as nuts and berries available year-round, scientists with Spain‘sBrown Bear Foundation say.
It is not yet known how the new strategy may affect the bears‘ ability to survive and reproduce.
For some species, however, the impacts of disrupted hibernation go far beyond an annoying case of insomnia.
"The first thing to keep in mind is that hibernation isn‘t a solutionto cold environments but to seasonally available resources," saidMurray Humphries of McGill University in Montreal, Canada.
Temperature is often a cue to enter or emerge from hibernation. But awinter warm spell doesn‘t guarantee that food will be available.
For example, bats that take flight in January, as seen this year in Quebec, find a sky bereft of insects.
"They may be just exploring—or they may be starving," Humphries said.
Colder is Better
It might seem that milder winters would make life easier for animalsliving in cold environments. A longer growing season for plants canmake more food available. And active animals require less energy whentemperatures are warm.
During hibernation, however, the cold actually helps animals conserve energy.
"The colder a hibernator can get, the more energy it can save,"Humphries said. "Without access to cold temperatures, hibernatingspecies face a problem—running out of energy before spring,"
Gregory Florant of Colorado State University has studied the effects of temperature changes on hibernating ground squirrels.
In warmer conditions the squirrels use up stored fat more quickly. Thisin turn reduces their levels of the protein hormone leptin.
"If you have lower leptin levels, your body tells you that you don‘t have enough food," Florant said.
As a result, the animals wake up both early and hungry, with little remaining energy to see them through to their first meal.
An early wake-up might not be a problem if plenty of food iswaiting just outside the den. But animals roused from hibernation bywarmer temperatures in late winter or early spring may find nature‘slarder bare.
Timing is Everything
A similar problem is encountered by species that complete northward migrations too early.
There are now dozens of examples of species migrating earlier than inyears past—and arriving to find an environment not yet prepared toaccommodate them.
Far fewer studies have been done on changes in hibernation patterns. But the phenomenon of early arousal may be widespread.
Perhaps the best data come from Colorado.
Researchers with the Rocky Mountain Biological Laboratory have trackedthe "first appearance" dates of migratory birds and hibernating mammalsover a 30-year period.
In this region spring temperatures have increased. But so has winter snowfall.
Yellow-bellied marmots that used to emerge from hibernation inmid-May now appear in mid-April. Hungry for grass and other plants, theearly-rising marmots often find their high meadows still covered by athick layer of snow.
"When they get up early in years with a dense snowpack, they starve orare eaten by predators," said biologist Dan Blumstein of the Universityof California, Los Angeles.
David Inouye of the University of Maryland published his firststudy on changes in marmot hibernation patterns in 2001. Since then,"the trends toward earlier emergence by marmots have continued," hesaid.
Strangely enough, golden-mantled ground squirrels and least chipmunks in the same region are actually hibernating longer.
"Chipmunks and ground squirrels may be using another cue," Inouye said, "perhaps the disappearance of snow from the burrows."