Pack size and wolf pup survival: their relationship under varying ecological conditions

Abstract

The relationship between pack size and two parameters of reproductive success (litter size at 7–8 months and pup weights at 5–6 months) were determined for two wolf (Canis lupus) populations in northern Minnesota. Pup weights were not correlated with pack size for either population. Litter size, however, was correlated with pack size, but the direction of the relationship varied between the two study populations. In the superior National Forest, where prey were scarce and the wolf population was declining from high densities, litter size and pack size were inversely related. Pairs produced more surviving pups than did larger packs with one or more potential helpers. In the Beltrami Island State Forest, where prey were relatively abundant and the wolf population was increasing, pack size and litter size were positively correlated. The results suggest that ecological factors, such as prey availability, affected the ability or willingness of various pack members to provide food or other care for the pups. The lack of correlation between number of auxiliaries and number of pups in canid populations with low and declining prey densities may be explained on the basis of heterogeneous prey density resulting in drastic annual variation in litter production. No study to date has measured the actual benefit that pups derive from helping by auxiliaries, and the costs and benefits of it. The relationships discussed herein can be considered valid only after such research is completed.