Kill rates and predation by wolves on ungulate populations in Bialowieza Primeval Forest (Poland)

Wolf (Canis hipus) kill rates, factors affecting their variation, and predation impact on ungulates were studied in the Polish part of Bialowieza Primeval Forest (580 km(2)). With the mean size of hunting groups being 4.4 individuals, wolves killed, on average, 0.513 +/- 0.04 prey.(pack)(-1).d(-1) (mean +/- 1 SE); 63% of prey were red deer (Cervus elaphus), 28% were wild boar (Sits scrofa), and 4% were roe deer (Capreolus capreolus). Per capita kill rate averaged 0.116 ungulates.(wolf)(-1).d(-1), and daily food intake was 5.58 +/- 0.32 kg.(wolf)(-1).d(-1). Kill rate on red deer was affected by snow cover (P < 0.001). A pack of wolves killed, on average, 0.264 deer/d in seasons with no snow and 0.587 deer/d when snow was 17 cm deep. The increase in kill rates coincided with a decline in the condition of juvenile (but not adult) deer in late winter (mean marrow fat content in the femur 66% in October-January vs. 27% in February-March). Per capita kill rates decreased slightly (not significantly) with the increasing size of wolf hunting group. However, the amount of food acquired per wolf did not differ among groups containing 2-6 individuals, because larger packs killed bigger prey more often and small prey less frequently than did small packs. Wolf kill rates on wild boar were higher in spring-summer (0.242 +/- 0.06 boar.(pack)(-1).d(-1)), when piglets were present, than in autumn-winter (0.106 +/- 0.04 boar.(pack)(-1).d(-1)). Annually, wolves killed on average 72 red deer, 16 roe deer, and 31 wild boar over a 100-km(2) area. Compared to prey densities, wolves were an important agent of mortality for red deer only, taking annually 12% of spring-summer (seasonally highest) numbers of deer, which was equivalent to 40%, of deer annual increase due to breeding and 40% of their annual mortality. Compared to winter densities (3-6 deer/km(2)), percentage predation by wolves was inversely density dependent; thus wolves limited deer numbers but did not regulate prey population. By eliminating a substantial proportion of the annual production of the deer population, wolves hamper its growth and prolong the time until it reaches carrying capacity of the habitat. However, wolf predation alone is a poor predictor of deer population dynamics, because deer are also subject to lynx (Lynx lynx) predation and hunting harvest.