Scavenging patterns of generalist predators in forested areas: the potential implications of increase in carrion availability on a threatened capercaillie population

The increases in ungulate populations and hunting bags throughout Europe and North America have resulted in higher carcass numbers available for mesocarnivore species in temperate and boreal forests. The increase in food resources can sustain denser predator populations, potentially affecting prey species such as the threatened western capercaillie Tetrao urogallus. We investigated the ungulate population trends in recent decades and the carrion use by facultative scavengers in areas of the Pyrenees occupied by capercaillie to assess the potential effects on predation of nests and adult birds, and on its population trend. We found a significant increase in the number of ungulates harvested during the period of sharp capercaillie population decline. Carrion was provided experimentally in forested areas occupied by capercaillie showing that remains were mainly consumed by red fox Vulpes vulpes, followed by wild boar Sus scrofa and marten species (Martes sp.). Season (cold or warm) was the most important factor determining scavenging activity in most species. Main predators of capercaillie nests and adults were martens and red fox, with no predation by wild boar. Our data show that main predators of capercaillie are the same species that mainly consume carrion, especially in winter, and that plentiful carrion resources could maintain higher populations of these species, potentially increasing predation pressure on the capercaillie population. This study shows that managing carrion arising from hunting activity in areas of capercaillie distribution is a necessary management action to reduce the available carrion biomass and so reduce the impact of mesocarnivores on capercaillie conservation.

We acknowledge the forestry rangers of Generalitat de Catalunya for field work. The comments of two anonymous reviewers improved the previous version. This work was funded by the Spanish Ministry of Science, Innovation and Universities (RTI2018-099609-B-C22) and the Spanish Ministry for the Ecological Transition and the Demographic Challenge.