Migration vs. Hibernation

"Family of Birds" by Octavio Ocampo

Some people used to think when the birds disappeared in the fall that they must be hibernating in tree hollows or caves. Other observers watching birds flying high in the sky thought they went to the moon to rest during the winter. Or perhaps they changed size and color and the robins would turn into juncos.

Don’t laugh. It hasn't been that long ago that we discovered through research like bird banding that titmice don’t ever go very far from the territory where they were born and that hummingbirds can fly thousands of miles south under their own steam in the fall and return to Michigan to nest in the spring.

And some birds do go into a mini-hibernation called torpor during the night. Torpor is a kind of deep sleep accompanied by drastically lowered body temperature, heart rate, and breathing. Hibernation is defined as a sustained state of torpor. Scientists have found that some birds like chickadees go into a nocturnal torpor to conserve energy during the winter. But just how they do this is still a mystery.

Today Seth Donahue, an associate professor of biomedical engineering at Michigan Tech University, is working in collaboration with scientists in Alaska to understand how bears survive on less oxygen during hibernation and can stave off osteoporosis.

Image via Wikipedia

A human who is bedridden for months will start to lose bone mass, but research shows that doesn't happen with bears. "Basically we found that there were no negative consequences of six months of hibernation on the bone strength or mineral content," says Donahue. “We have found that the bears’ resistance to osteoporosis during hibernation is almost certainly linked to calcium recycling. During hibernation, other animals excrete the products of bone breakdown, but bears do not. Urea, calcium and phosphate are recycled. Bears in hibernation produce urine at a very slow rate and then reabsorb it through the bladder.”

He is testing a drug derived from black bear parathyroid hormone, an amino-acid-based hormone that provides better bone-building properties. This would help people that are bedridden or perhaps people on long space missions.



Read more on the benefits of the study of hibernation in Arctic Lessons by Kalb Stevenson in Alaska Magazine — March 2011