Calves dying because plants unavailable, study says

Caribou calves are dying more frequently in West Greenland because of climate change, says a new study.

Eric Post, a biology professor from Penn State University, found a fourfold increase in calf mortality since 1993. His research links these deaths with a temperature increase of 4°C, which has pushed the growing season of plants forward by two weeks.

As a result, there's less nutrition available when young calves are at their most vulnerable.

Scientists call the problem "trophic mismatch." It is created, in a sense, because caribou and plants tell time differently. Plants grow when the temperature warms. Caribou migrate to calving grounds when the days grow longer.

These two events used to occur at the same time. But not any more.

The best-known example of trophic mismatch, documented in Al Gore's movie "An Inconvenient Truth," involves Dutch birds and their caterpillar prey. Post's work is the first to examine trophic mismatch among terrestrial mammals.

Post's findings are being published in July in the journal Philosophical Transactions of the Royal Society. His paper warns caribou may continue to drop in number as the climate warms.

However, there is some evidence that caribou may adapt. It's found on the sub-Antarctic island of Georgia, where Norwegians introduced caribou in the early 20th century.

These caribou initially gave birth at the usual time, in May. The calves died, because May is the onset of winter in the sub-Antarctic. But eventually female caribou adjusted their reproductive cycles.

Two herds continue to dwell on the island today, in the company of a large colony of king penguins.

Even so, Arctic caribou face other threats brought about by climate change other than trophic mismatch.

Freezing rain coats the tundra with ice and prevents caribou from eating lichen. And wet snow takes a lot more energy for caribou to walk through.

Post attributes these weather-related threats to declines in the number of both caribou and muskox in Greenland and Svalbard, in a paper published in 2006.

And he raises the question of whether these animals will survive in a warmer Arctic, or join camels, deer, antelopes, woolly mammoths and other extinct animals that once roamed the sub-Arctic before the last Ice Age, more than 10,000 years ago.

It's long been held these beasts died from over-hunting. But Post's earlier paper, published in the journal Quaternary International in March 2006, points to recent evidence that suggests the animals died following the encroachment of warm weather.