for National Geographic News
Greenland's caribou work up quite a hunger during their long migrations. But global warming now has the animals arriving late for dinner—and paying a heavy price.
Fewer caribou calves are being born in the western part of the Danish island, and those that are born have slimmer chances of surviving, a new study reports.
The declines are tied to availability of the willows, sedges, and flowering tundra herbs that caribou and their newborns feed on in spring.
As global warming causes these plants to bloom ahead of schedule, herds are arriving when the bounty is past its peak.
"For these animals, the cafeteria is closing earlier and earlier," said Eric Post, a Pennsylvania State University biologist who co-authored the new study with Mads Forchhammer of the University of Aarhus in Denmark.
Caribou haven't adjusted their arrival time, because they rely not on temperatures but on the steady lengthening of daylight hours to mark the onset of the calving season.
"The problem is twofold: Not only can't you rely on getting the best meal when you're most hungry, you also can't rely on being able to keep up with changes to the cafeteria's opening hours in the future," Post said.
The exact impacts of this developing "trophic mismatch" are still unclear.
"Alone, trophic mismatch might not be the most important factor," Post said, "but it might be the spark that ignites the forest fire when other factors converge."
Caribou, also known as reindeer, depend on tundra plants. During the Arctic's frigid winter months, they find sustenance mostly from lichen, which they dig from under the snow.
As spring approaches, longer days spur the females to migrate to areas where plants are more abundant so they can give birth.
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