August 24, 2009

Muskoxen keep warm better than thought

An Australian scientist says he has found, contrary to theory, young Arctic muskoxen conserve heat nearly as well as do adults.

Biologist Adam Munn of the University of Sydney said young animals theoretically should have a harder time holding heat because they have larger ratios of surface area to body volume, meaning more of their body mass is directly exposed to the cold.

That theory appeared to hold true for muskoxen, with scientists reporting high death rates for muskox calves during especially cold winters in their arctic habitats.

But Munn and his team measured heat loss in adult and young muskoxen and discovered smaller calves were no more thermally stressed than larger adults.

Munn's team observed a population of muskoxen at the University of Alaska's Large Animal Research Facility in Fairbanks. They used infrared sensors to measure heat loss from the body surface of animals in contact with cold air and the frozen ground.

The researchers found both calves and adults sacrificed only 2 percent to 6 percent of their daily energy intake to heat loss during foraging bouts, even when temperatures dipped to minus 58 degrees Fahrenheit.

This suggests that any thermoregulatory constraints associated with a small body size may not be as important for calf survival as previously thought, Munn said.

The study is to appear in a future issue of the journal Physiological and Biochemical Zoology.