Body weight, body condition and structural size of Scandinavian wolves

Abstract: Large carnivours are suffering from population declines all over the world, but many have also recolonized parts of their previous habitats. However, recovery by these species is usually slow and challenging. The population sizes are therefore often small and semi-isolated which can lead to lowered health, fitness and survival for these individuals. The objective of the present study was to investigate the effects of age, sex, inbreeding, conditions in natal territory (wolf density and food availability) as well as season on three body size measurements; body weight, body condition (residuals from a regression of body weight and body length) and structural size (a principal component analysis of body length, ear length and tail length) in the Scandinavian wolf (Canis lupus) population. Two different data sets were used, alive wolves measured when captured (1998 – 2014, n = 159), and dead wolves measured during necropsy (1999 – 2020, n = 329). Males were larger than females and older wolves were larger than younger. Increased level of inbreeding had a negative effect on both body weight and structural size but not on body condition. An increase with 0.1 of the inbreeding coefficient resulted in 1 kg decrease in body weight. The lack of effect on body condition could possibly be due to external circumstances rather than to congenital inbreeding. Food availability in natal territory did not have an effect on any of the size measurements, while wolf density had a positive effect on all three body size measurements. This could possibly be due to the surplus of food seen for this population and may be due to younger wolves are shown to stay with with their parents for longer when wolf densities are high and therefore maybe gaining more food per wolf per day. Body weights were mainly larger in winter than in summer. These results provide knowledge about factors affecting both body size and body condition, and therefore also indications of the health and fitness of the Scandinavian wolf population. This is important for future conservation, as this study shows the importance of management aimed to reduce inbreeding to achieve a more healthy wolf population eventhough the population is growing.