The Vertebrate Scavenger Community Along a Boreal Forest-Alpine Gradient: The Importance of Ungulate Management, Small Rodent Cycles and Winter Climate

While the importance of carrion and scavenging is increasingly acknowledged, there are relatively few empirical studies of the scavenging community in Fennoscandia. There is limited knowledge on how habitat and potentially important drivers like winter climate, productivity, human subsidies or small rodent cycles affects the scavenger guild. The objectives of my thesis were to investigate 1) the structure of the winter scavenger community across a forest-alpine gradient in central Scandinavia and the effects of temperature and snow depth; 2) effects of large quantities of gut piles left behind during the moose (Alces alces) harvest on scavenging communities and the influence of energy content and gut pile density on scavenging patterns; 3) how fluctuating small rodent abundance, landscape productivity and snow depth affected red fox scavenging during autumn and winter in forest and alpine habitat. To meet these objectives camera traps were set up on gut piles from moose harvest in autumn and on baits consisting of frozen blocks of discarded reindeer (Rangifer tarandus) meat, fat and connective tissue in winter. Spatial variation in snow depth along the forest-alpine gradient interact with habitat to shape the structure of the scavenger community, while the impact of snow depth and temperature on species richness were weak in both forest and alpine habitats. When examining species separately diverse effects were observed, and most variation in individual species occurrence at baits was also explained by snow depth and habitat. Increasing snow depth only had negative effect on occurrence at baits for the species with stronghold in forest. The habitat generalists, and the alpine species showed no effect from climatic conditions at baits in alpine areas, but occurrence at baits in forest declined with decreasing snow depth and increasing temperature for red fox (Vulpes Vulpes), common raven (Corvus corax) and wolverine (Gulo gulo). Besides from the forest species Eurasian jay (Garrulus glandarius) which had a high probability of occurrence in forest, the habitat generalists red fox, common raven and golden eagle (Aquila chrysaetos) dominated in both habitats. Depletion of gut piles was dependent on the different quality of gut pile parts, the energy rich parts were depleted first, and several times faster than the parts with lower energy content. This resulted in large differences in the magnitude and the duration between the parts with high and low energy content, where the latter accumulated to higher densities and was present a long time after the end of the moose hunting season. Corvids arrived early at gut piles and their presence at gut piles decreased with gut pile age, probably reflecting depletion of gut pile parts with high energy content. Mammal presence at gut piles peaked at intermediate gut pile densities and I propose that lower mammal presence at high gut pile densities is due to resource saturation during this period. I found contrasting patterns of red fox scavenging between forest and alpine habitat. I suggest that variation in red fox presence at alpine baits between the different phases of the small rodent cycle mostly reflects variation in red fox abundance. High red fox presence at alpine baits in the winter after the peak in rodent abundance is probably a numerical response, reflecting high red fox reproduction the preceding summer. In forest I found scavenging patterns probably reflecting a functional response. Red fox scavenging increased with low small rodent availability, when the snow was deep during winters of low small rodent abundance. Red fox scavenging on gut piles in autumn was not affected by small rodent phase, which may imply that gut piles is not a secondary choice for foxes