Winter Weight Dynamics in Microtus Pennsylvanicus

A population of meadow voles 75 mi northeast of Winnipeg, Manitoba, Canada was live-trapped biweekly for two winters and it is suggested that weight loss is not simply a result of lack of food, but is an adaptive response cued by some factor such as day length.

Abstract

A population of meadow voles (Microtus pennsylvanicus) 75 mi northeast of Winnipeg, Manitoba, Canada was live—trapped biweekly for two winters. From August to February of each year the mean population weight decreased by 30% to 40%. This decrease was not due to preferential death of the heavier animals because their survival was better than would have been expected if survival and weight were independent. part of the weight loss was due to the immigration of young animals that failed to gain weight. However, much of the decrease in mean weight was due to that lost by individuals, because many samples of animals released and recaptured 2 wk later had lost significant amounts of weight. Four marked ♂ ♂ trapped from August to February lost an average of 28.6% of their weights while 14 marked ♀ ♀ lost 45.5% in the same time period. In February the mean weights of individuals and the population began to increase. It is suggested that weight loss is not simply a result of lack of food, but is an adaptive response cued by some factor such as day length.