Comparing body condition of moose (Alces alces) selected by wolves (Canis lupus) and human hunters: consequences for the extent of compensatory mortality

Abstract

Predators commonly select prey of inferior quality compared with the average animals found in the population. Consequently, predation may often be compensatory to other sources of mortality. We tested whether wolves ( Canis lupus L., 1758) in Scandinavia selected moose in poor body condition by comparing mandibular marrow fat (MMF) of wolf-killed moose ( Alces alces (L., 1758)) with harvested moose. Model selection analyses indicated that MMF levels were lower for wolf-killed moose compared with harvested moose, but an unbalanced sample design between years for the two causes of death (wolves and harvest) may have confounded a clear interpretation of the results. Nevertheless, corrected MMF levels (to 1 April) showed that a significantly (p = 0.006) higher proportion of the wolf-killed calves (18.5%) were below the level often assumed to reflect acute malnutrition (<20% MMF) compared with harvested moose calves (3.3%). For wolf-killed yearlings and adult females, 5.6% and 8.3%, respectively, had MMF below this level compared with 0% for harvested individuals. As a result, 15.1% of the total number of wolf-killed moose and 1.6% of the harvested moose during winter appear to be compensatory to mortality from starvation. Differences in body condition, and thus levels of compensatory mortality, found between wolf-killed and harvested moose in this study may reflect a stronger selection for individuals in poor body condition by wolves.