Arctic ice melt due to global warming is having an unexpected impact on West Greenland's caribou, causing fewer calves to be born and boosting their death rate, a study said today.
Accelerated ice melt has caused the plant growth season on Greenland to start ever earlier -- about 16 days sooner on average in 2011 than in 2002, scientists wrote in the journal Nature Communications.
The calving season, though, has stayed the same.
This means the newborns and their mothers have to eat older plants that are past their nutritional peak.
Greenland's caribou, big elk-like animals with antlers, closely related to wild reindeer, have for about 3,000 years been arriving from a west-to-east migration in late May to early June in search of young plants -- willows, sedges and flowering tundra herbs -- as they are about to give birth.
Eating juicy young plants at this time increases the chances of healthy offspring.
After a long Arctic winter having to dig through the snow to find lichens, "the animals show up expecting a food bonanza, but they find that the cafeteria already has closed," because of the altered growth season, said Jeffrey Kerby, a Penn State University graduate student who contributed to the report.
The ongoing decline in sea ice has been associated with higher land temperatures in many parts of the Arctic.
Plants respond to warmer temperatures by adjusting the timing of their growth, said the study authors.
But caribou, whose reproductive cycles are timed by seasonal changes in daylight length rather than temperature, continue to give birth at nearly the same time during spring.
"This scenario is what we call a trophic mismatch -- a disconnect between the timing of when plants are most nutritious and the timing of when animals are most dependent on them for nutrition," Kerby said.
Study co-author Eric Post, a Penn State biology professor, started studying the relationship between caribou calving and the Greenland plant-growing season 20 years ago.
The pair also used data from a 1970s study, when there was much higher calf production and survival in the area.
"Sea ice is part of a broader climate system that clearly has important effects on both plants and animals," said Post.
"Exactly how sea ice decline might affect species interactions in this and other types of food webs on land in the Arctic is a question that deserves greater attention.