Food Preference, Optimal Diet and Reproductive Output in Stoats Mustela Erminea in Sweden

Abstract

Field data on the diet of stoats in relation to different prey density were used to examine food preference and selective feeding and to test predictions from optimal foraging theory. The relationship between diet and reproductive output was also examined in three food environments. Stoats concentrated on voles (their basic food) when vole density was high or moderately high. Male stoats showed a high preference for the larger water voles. Selective hunting for them increased with their relative abundance but the males specialized less on water voles at overall high density of rodents. This was probably due to high relative density of the prey second in preference (field vole). The data are in agreement with the theory predicting relative density of prey to be important in determining optimal diet. Females did not show any clear preference for water vole relative to field vole and no long term change occurred in selective hunting relative to changes in vole density. The difference between males and females was ascribed to different fitness set functions, implying a combination of large and small voles to be the optimal diet for females and large prey as water vole as optimal diet for males. No consistent difference in reproductive success was found in the different food environments, but the highest reproductive output occurred in areas with relatively high water vole density.