Struggling to adapt to global warming, wildlife species are changing their diets, behaviors and, in a few cases, even their genetic makeup
- Jessica Snyder Sachs
- Dec 01, 2009
As a security officer on Alaska’s Prudhoe Bay oil field, Bill Petersen is charged with duly recording unusual occurrences. So his video camera was within easy reach on a dim November evening when he spotted a red fox chasing an Arctic fox out from under a building erected on stilts. Small and snowy white, the native Arctic foxes have always been a familiar sight around the oil field operations, especially in winter, when a natural drop in prey sends them dumpster diving. In recent years, Petersen and his coworkers have also been seeing larger and lankier red foxes—more common to forests south of the Alaskan tundra. Sometimes they would glimpse one of the reds chasing Arctic foxes from the camp garbage.
But this was different. As Petersen watched, the red fox continued its chase—beneath several trucks and out over a parking lot. As the two foxes began to tumble and fight, Petersen started filming. The Arctic fox bit and kicked as it rolled beneath an aggressor nearly twice its size. It took 10 seconds for the red fox to find its mark. Biting the smaller fox above the shoulders, it gave a quick, neck-breaking shake. Petersen continued filming as the red fox trotted across the parking lot—its prey hanging limply from its jaws—to a patch of snow where it began eating. Petersen’s video, which found its way to the University of Alaska’s Institute of Arctic Biology, was the first recorded instance of a red fox preying on its smaller cousin in Alaska. But it may not be the last, says institute biologist Erich Follmann. Since the video was taken in 2004, Follmann and colleague Nathan Pamperin have interviewed other oil field workers who have reported similar incidents.
Certainly the red fox has dramatically expanded its range northward, Follmann says, and global warming is the likely cause. “I’ve been up on the North Slope since 1976,” he explains. “Thirty-three years ago it was unheard of to get temperatures in the 60s or 70s, even in the summer. Now it’s not uncommon. And 33 years ago, you’d occasionally get a red fox as far north as Barrow. Now in some oil field areas, they’re taking over.”
TRYING TO ADAPT
Several years have passed since studies conclusively demonstrated that global warming is altering where and when many animals feed and breed. In 2003, two benchmark reports showed that more than 100 species had shifted their range toward the poles at an average of 4 miles a decade, and that thousands of others were emerging, migrating or breeding days to weeks earlier than they did a century ago.
But animal species differ in the way they adapt to climate change. As a result, range shifts by animal populations can create problems with animals that remain in their historical ranges. Similarly, changes in seasonal timing can knock animals out of sync with the seasonal appearance of the plants and prey they need to survive.
Now a scattering of reports from around the world suggest these mismatches may be producing a new level of behavioral changes. “We’re seeing a pattern here,” says Camille Parmesan, a biologist at the University of Texas, Austin. “The first kinds of behavioral changes were changes in range and timing. Now we’re seeing changes in diets and other behaviors that show some animals are trying to adapt to their new circumstances. Unfortunately, many instances are more an act of desperation than a true adaptation.”
BEARS ON THIN ICE
Ice cap melting spells even bigger trouble for polar bears. That’s because ringed seals give birth on the ice in April and May, providing the bears with the bulk of the calories and fat they need to survive the lean summer ahead. “With the ice breakup advancing three weeks over the last 30 years, that means a lot of thin and hungry bears coming onto land each spring,” explains Ian Stirling, a veteran polar bear biologist with the Canadian Wildlife Service.
Already, this has sent increasing numbers of polar bears into Inuit towns and hunting camps. At the same time, the first bears to come off the ice each spring are beginning to overlap with the nesting season of Arctic geese and ducks. Some experts believe this may be turning an occasional deviation—a polar bear snacking on eggs—into a regular habit. “We’re definitely seeing an increase in the last five to six years,” says snow goose expert Robert Rockwell of the American Museum of Natural History.
An increase in egg-gobbling polar bears is affecting the colonies of snow geese Rockwell studies along the shores of northern Manitoba’s La Perouse Bay. But this might turn out to be a good thing, he hastens to add. “In 1969, this goose colony had around 2,500 nesting pairs,” he explains. “Now it’s over 50,000.” This population explosion may stem from the increased availability of corn and rice in the goose’s wintering grounds across the northern plains. “Lots of people think it’s cool to see these beautiful funnel clouds of snow geese,” Rockwell says. “Problem is, the Arctic environment is very fragile, and these guys have beaten it to death.”
The snow goose’s nesting time is also advancing with global warming, Rockwell says, though more slowly than the advance in the polar bear’s arrival on land. At present, the bears are overlapping with the tail end of snow goose nesting. But if current trends continue, Rockwell calculates that the bears will be present during the middle of nesting season in about four years. That could help control snow goose populations.
More controversial is Rockwell’s suggestion that the new food source could help save hungry polar bears. Veteran polar bear biologists such as Stirling scoff at that idea. “An adult polar bear needs to eat around 43 ringed seals or the equivalent to make it through a year,” Stirling points out. “That’s a huge amount of biomass that makes the seasonal intake of goose eggs by a few polar bears look trivial.”
John Kostyack, NWF’s executive director for conservation and global warming, agrees. “Look at the species already on endangered lists,” he says. “Most are there because they are habitat specialists. They have very specific needs, and as a result of human activity, their habitat is changing. Add the stress of climate change, and it may be enough to tip them over to extinction.” Clearly, some of the new behaviors being reported are making a bad situation worse. Red foxes preying on Arctic foxes may be a case in point. Already, global warming has begun melting the polar ice cap where some Arctic foxes hunt in winter. This reduces the species’ hunting range. But it also cuts off a potential escape route. “With the ice forming later in fall and melting earlier in spring, it’s going to constrict the time that Arctic foxes can get away from red fox predation,” Follmann says.
COPING WITH CHANGE
In a handful of cases, animals are clearly adapting to global warming—at least in the short term. In Britain, for example, great tits appear to be coping well. These beloved songbirds are laying their eggs earlier in spring, keeping in step with earlier emergence of the caterpillars needed to feed their chicks. Specifically, the British great tits are laying their first clutch of eggs about two weeks earlier than they were 50 years ago. The bird’s egg laying and the caterpillar’s emergence both appear linked to temperature, concludes Oxford University ecologist Ben Sheldon.
But just across the North Sea, in the Netherlands, great tits are not doing so well. They, too, have advanced their egg-laying over the years, but not at the pace or to the extent of their British counterparts. As a result, the time when chicks need the most food now lags behind the peak in caterpillar biomass by nine days, reports Marcel Visser of the Netherlands Institute of Ecology. Visser believes this mistiming accounts for a dramatic drop in “double brooding” among his country’s great tits. In the 1950s, he says, most of the birds produced a second clutch of chicks each season. Now as few as 5 percent manage to do so. Linking this decline back to climate change, Visser found that only when a female’s first clutch of chicks coincides with peak caterpillar abundance is she likely to produce a second brood. Sheldon and Visser are now collaborating on studies that might reveal what helps and what hinders animals struggling to adapt to global warming.
Biologists use the term “behavioral plasticity” to describe flexibility on the part of individual birds, bears, foxes and other animals. By contrast, many survival instincts are hardwired into an animal’s genes. Changes in day length, for example, trigger migration, mating or hibernation in many species. Many insects and other invertebrates are also preprogrammed to respond to set images of what to eat or where to lay their eggs. “A change in these responses requires wholesale changes in genetic makeup,” Parmesan explains.
But that’s just what she and other researchers say they are seeing in a few cases. One may involve a West Coast butterfly called Edith’s checkerspot. In the 1990s, Parmesan’s discovery that this butterfly had shifted its range north was one of the first to show a clear relationship to global warming. The delicate orange, black and white-checkered butterfly is sensitive to temperature because host plants such as plantain dry out in hot weather. With the plants drying out earlier and earlier each year, fewer of the butterfly’s caterpillars were surviving to adulthood.
In 1996, Parmesan reported that three-fourths of the butterfly’s southern populations had disappeared. Worst hit was an endangered subspecies, the Quino checkerspot of Southern California and Mexico. Looking at a map, she predicted that the Quino “was a goner. It couldn’t go north. There was nothing but desert.”
But seven years later, Parmesan began hearing reports of new Quino populations in the San Jacinto foothills east of San Diego—outside of the butterfly’s known historic range. “Instead of going north,” she marvels, “it may be heading up.” Species retreating up mountains to escape global warming wasn’t new. But the new upland populations were also laying eggs on a plant—Chinese houses—the Quino had never before been seen using.
“This may represent a kind of genetic revolution,” Parmesan says. That’s because a butterfly shifting to a new host plant has to change more than the genes governing its search image and host preference—that is, its instinct to lay eggs on a particular plant. Other necessary genetic changes may include the number of eggs being laid—something that must match the plant’s ability to shelter them and nourish the emerging caterpillars. Sometimes, caterpillars even need to produce new enzymes to detoxify a different plant’s natural pesticides.
In general, insects and other animals with short life cycles and large broods stand the best chance of making such rapid genetic adaptations. This isn’t to say that the exceptional bird or even mammal can’t make an evolutionary leap. One of these unusual creatures appears to be the Yukon red squirrel. During the 1990s, biologist Stan Boutin of the University of Alberta led studies showing that females were giving birth 18 days earlier, on average, than their great-grandmothers had a decade earlier. Only part of the change could be explained by global warming increasing the amount of food available earlier in spring. Further study showed clear selection for mothers with genes prompting earlier breeding. It helps that female squirrels can, in Boutin’s words, “crank out babies like crazy”—a factor that can speed the spread of any successful genetic trait.
“Unfortunately, most species have much slower reproductive cycles,” Kostyack says. “The climate change we’re seeing is far faster than their ability to evolve. As a result, their survival will require people to change in two significant ways. We need to both reduce our carbon footprint to slow global warming, and we need to strengthen environmental protection in a way that makes habitats more resilient in the face of climate change.”
New Jersey journalist Jessica Snyder Sachs wrote about newly discovered populations of rare species in the October/November 2009 issue.
Help Monitor Wildlife and Warming
Since 2007, the USA National Phenology Network has enlisted professional and citizen scientists nationwide to record changes in the seasonal timing—or phenology—of leafing, blooming and fruiting of more than two dozen North American plant species. This year, the organization will expand its efforts to monitor the timing of breeding, hibernation, migration and other seasonal behaviors of several animal species, including yellow-bellied marmots, ruby-throated hummingbirds, northern painted turtles, wood frogs, coho salmon and bumblebees. Learn how you can help at www.usanpn.org.
Unnatural Acts: Tiger Attacks on Humans
In South Asia, a global warming-related rise in sea level is gradually flooding coastal mangrove forests in the Sundarbans of Bangladesh and India—habitat for one of the world’s largest surviving tiger populations in a unique ecosystem. That, in turn, may be partly responsible for a recent increase in tiger attacks in surrounding villages. “It is very rare that a tiger walks through human habitation unless it has no other option,” says Mahendra Shrestha, director of the National Fish and Wildlife Foundation’s Save the Tiger Fund. “Now we’re frequently seeing tigers straying from their habitat.” As an example, Shrestha describes a tigress that recently wandered 125 miles or more from the nearest tiger habitat. Walking through Indian towns and villages, she killed four people before being shot.
NWF Priority: Fighting Global Warming
NWF is shaping and supporting proposed federal legislation to combat the global warming that is changing the behavior of wildlife, from Arctic foxes and polar bears to songbirds and endangered butterflies. On other fronts, NWF’s Campus Ecology® program is promoting alternative energy projects and sustainable practices at colleges and universities across the country. Through its Eco-Schools USA, Climate Classroom and other education programs, NWF also is creating elementary and high school curricula that focus on global warming and its solutions. To learn more about these efforts, go towww.nwf.org/globalwarming, www.nwf.org/ecoschools and www.climateclassroom.org.