Fewer Caribou Born as Warming Causes Missed Meals

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But temperature climbs of 7 degrees Fahrenheit (4 degrees Celsius) in recent years have caused peak plant availability to occur earlier, impacting caribou birth and survival rates.

Caribou are the first terrestrial mammals to be documented with a trophic mismatch, the study authors say.

Other affected species, such as great tit birds in England, have been able to adjust, and Post and Forchhammer say it's possible caribou could also adapt to shifting plant cycles.

In fact, caribou have survived many climate fluctuations in the past.

Morten Meldgaard, director of the Natural History Museum of Denmark, compiled in the 1980s a comprehensive study of historical population data on Greenland's caribou.

"Over the past 250 years there have been a number of cycles in populations," he said.

By observing climate shifts during that same time period, Meldgaard was able to "pinpoint a relationship between climate change and caribou calving populations."

The data show that athough they didn't always fare well, caribou populations did survive more than two centuries of climate changes.

Juggling Factors

Caribou also survived an ancient period of dramatic warming—the Pleistocene-Holocene transition some 10,000 to 12,000 years ago.

But given today's rapid and unpredictable rate of climate change, Post believes the future of modern caribou is uncertain.

"If this were the only factor caribou had to contend with, they would undoubtedly adjust if the rate of environmental change were constant," he said.

The current rate of change could accelerate, decline, or—worst of all for caribou—fluctuate unpredictably.

"Add on top of this the fact that these caribou are also constrained by other factors like winter conditions, population density, human land use, hunting pressure, parasite loads, and competition with musk oxen," he said.

"Suddenly, there's another ball in the air that the juggler has to keep track of."

The study, to be published this summer in the Philosophical Transactions of the Royal Society of London, was partially funded by the National Geographic Society's Committee for Research and Exploration.

(National Geographic News is part of the National Geographic Society.)

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