Cannibalistic necrophagy in red foxes: do the nutritional benefits offset the potential costs of disease transmission?

Cannibalism, or intraspecific predation, occurs when an individual consumes another individual of its own species; c.f. ‘cannibalistic/conspecific/intraspecific necrophagy’ when the individual consumes all or part of a dead conspecific. These behaviors are widespread across animal taxa but are considered rare among mammalian carnivores. The consumption of conspecifics could involve ecological and nutritional benefits in providing high-quality resources. However, it can carry potential risks such as those related to pathogen transmission. Despite this, the overall role of conspecific consumption in disease transmission among animals has received little attention. Here, we report the first direct observations of cannibalistic necrophagy in red foxes Vulpes vulpes. Our photographs of this behavior prompt speculation on the role of cannibalism in fox population dynamics and intraspecific disease transmission. We placed six fox and seven lamb carcasses of similar size to determine possible differences in the scavenging behavior of red foxes between dead conspecifics and heterospecifics. Conspecific necrophagy was recorded at all fox carcasses, involving foxes scavenging fox carcasses at different stages of decay. Carcass detection time by foxes was similar at both fox and lamb carcasses, but lambs were completely consumed in a shorter period, evidencing a preference for heterospecific consumption. Our findings contrast with other studies which argue that cannibalism avoidance in mammalian carnivores is due to an evolutionary strategy to reduce the probability of disease transmission. In fact, our observations of conspecific necrophagy provide direct evidence against the parasite-avoidance hypothesis, suggesting that carnivore and conspecific carcasses can represent an alternative trophic resource for foxes in certain areas and circumstances.