Prey Selection and Foraging Characteristics of Least Weasels (Mustela nivalis) in the Laboratory

-Foraging behavior and food selection of least weasels (Mustela nivalis) were investigated with respect to size and behavioral characteristics of Microtus pinetorum adults, M. pennsylvanicus adults and juveniles, and Peromyscus leucopus adults and juveniles offered as paired comparisons. The weasels attacked virtually all prey offered, thus exhibiting opportunistic foraging behavior, but did not capture all prey types with equal frequency. Microtus pinetorum were captured most frequently and M. pennsylvanicus adults were captured least frequently. The high vulnerability of M. pinetorum was attributed to their slow movements and ineffective escape tactics. The much lower capture rate for M. pennsylvanicus adults was attributed to their large body mass and aggressive behavior towards attacking weasels. The results indicate that relatively large, aggressive and active prey are less vulnerable to weasel predation than small, inactive or nonaggressive, intermediate-sized prey.