A fascinating new study in the January/February 2007 issue of Physiological and Biochemical Zoology looks at the benefits of huddling vs. solitude, comparing strategies used by striped skunks to get through long, cold winters in northern climates. While most male skunks den underground alone during the winter, a group of female skunks will often snuggle together with one male in communal dens.
Yeen Ten Hwang (University of Western Ontario) and coauthors found that skunks that choose to go it alone reach torpor - the state during which an animal reduces its metabolism and lowers its temperature to save energy and conserve water - almost ten times more every day. Indeed, the researchers were surprised to find that male skunks who huddle with females do not enter torpor at all, perhaps staying physically alert to defend the den.
"Contrary to our predictions, grouped skunks did not regularly use torpor in addition to huddling to maximize energy saving," write the authors. "Our results revealed a different strategy for animals in groups: When skunks were in groups they apparently benefit from huddling to the point of reducing the need to undergo torpor."
Huddling in groups minimizes the proportion of exposed surface area and water loss to the environment. Communal skunks emerge in the spring with a higher body fat percentage (25.5 percent, compared with only 9.3 percent for solitary skunks). Male skunks that huddle with females also benefit reproductively, as studies have shown that low body temperature can lead to difficulties with sperm production. Why don't all skunks form communal huddling groups in the winter? The authors point out that there is a higher risk of disease or parasite transmission in communal dens. In addition, predator detection and depletion of resources are also a risk of communal dens.
"The fitness benefits of spring body fat are probably higher in females than males because of higher reproductive cost incurred by females for pregnancy, parturition, and lactation," explain the authors. "Thus, the benefits of communal denning in females outweigh the cost, whereas for males the cost of communal denning must outweigh the benefits of higher body fat in the spring."
Although torpor is most well studied in larger animals such as bears, it is also observed in striped skunks and badgers in the northern parts of their range. In fact, striped skunks can reach the lowest known torpid body temperature of any carnivore, 26 degrees Celsius.
Since 1928, Physiological and Biochemical Zoology has presented current research in environmental, adaptational, and comparative physiology and biochemistry. Original research results represent a variety of areas, including thermoregulation, respiration, circulation, osmotic and ionic regulation, environmental acclimation, evolutionary physiology, and metabolic physiology and biochemistry.
Yeen Ten Hwang, et al. "Energetic consequences and ecological significance of heterothermy and social thermoregulation in striped skunks (Mephitis mephitis)." Physiological and Biochemical Zoology: 80:1.