Mountain Goats Are Shrinking - A Lot - Because of Global Warming

Chamois goats in the Italian Alps have gotten smaller over the past few decades.

Wild mountain goats in the Italian Alps have gotten significantly smaller over the past few decades in response to a warming climate, scientists reported Tuesday.

Although global warming is known to be driving changes in body size in a number of animals, this result was more dramatic than researchers expected and suggests that a changing climate may have significant impacts on natural systems in the near term, in ways that are only beginning to be understood.

Young Alpine chamois mountain goats (Rupicapra rupicapra) now weigh about 25 percent less than animals of the same age did 30 years ago, scientists at Durham University in the U.K. reported in the journal Frontiers in Zoology.

At the same time, temperatures where the goats live have risen by 3° to 4° Celsius, or 5° to 7° Fahrenheit.

"Over the past few years there's been quite a few papers coming out showing that all sorts of species, from mammals to fish to birds, have tended to get smaller as climate warms," says Stephen Willis, a study co-author and professor of biology at Durham University.

But scientists hadn't expected such a significant change among the Alpine goats in such a short period, says Willis.

Willis adds that scientists "don't know enough about how extreme climate might affect the population of this species," but he said continued warming might be a problem for the animal's survival in the future. As it stands, though, the population has actually increased over the past few decades.

Too Hot to Eat?

Willis says he and his colleagues discovered the change in body weights by measuring carcasses of yearlings collected by hunters since the 1980s. The researchers studied yearlings rather than adults to be sure of comparing animals of the same age. When they noted a steady decrease in size for animals that were all one year old, they began looking for a cause.

Decreases in food availability or quality as a result of global warming have been implicated in size declines in other species. But satellite data showed no decline in vegetation in the Italian Alps over the past few decades.

Next, the scientists considered the goats' behavior. "It's been known that these animals spend more time resting when it's hot, so that led to the idea that maybe it's the climate directly that is changing their behavior, rather than the indirect means of affecting their food," says Willis.

In other words, the scientists think that the goats are avoiding overheating in a warmer world by spending more time resting and less time foraging. That has reduced their body weight—which may be further reinforcing their ability to withstand the heat. In a given species, smaller animals shed heat faster than larger ones because they have more surface area relative to their body mass.

A factor unrelated to climate change may also be contributing to the size decline, however. The goats' population density has been rising, possibly due to greater restrictions on hunting. That may have increased competition for prime grazing spots, which may have helped keep their weights down.

Are They Really Better Off Small?

Clifford Rice, a wildlife biologist with Washington State's Department of Fish and Wildlife who studies mountain goats, says the fact that the scientists had such a long record of weights to go on is highly unusual. Such data are especially rare in North America, says Rice, who was not involved in the study.

In general, says Rice, "there is the potential for threats to mountain ungulates around the world due to climate change, including shrinking habitats, but exactly what those consequences might be we don't know yet."

The declining size of the Italian chamois has a potential downside, Willis and his colleagues write: Lighter goats don't overheat as easily, but they may be more susceptible to freezing to death in harsh winters. The balance of the two effects will depend on whether winters warm as much as summers in the Alps.

Willis notes that the team's findings may have wider implications for other species, or even domestic animals.

"If climate change results in similar behavioral and body mass changes in domestic livestock, this could have impacts on agricultural productivity in coming decades," he says. Translation: Farm animals that eat less produce less meat.