In the Arctic tundra, recurrent periods of food scarcity force predators
to rely on a wide variety of resources. In particular most predators use
ungulate carcasses as an alternative food supply, especially in winters
when live preys are scarce. As important and localized resource patches,
carrion promotes co-occurrence of different individuals, and its use by
predators is likely to be affected by interspecific competition. Here,
we studied how interspecific competition and resource availability
impact winter use of carrion by Arctic and red foxes in low Arctic
Fennoscandia. We predicted that presence of red foxes limits Arctic
foxes' use of carrion, and that the outcome of competition for carrion
depends on the availability of alternative food resources, such as
rodents. We monitored Arctic and red fox presence at experimentally
supplied carrion using camera traps, between 2006 and 2021 in late
winter. Using a multi-species dynamic occupancy model at a week-to-week
scale, we evaluated use of carrion by foxes, while accounting for the
presence of competitors, rodent availability and supplemental feeding
provided to Arctic foxes. Competition primarily affected carrion use by
increasing both species' probability to leave occupied carcasses to a
similar extent, suggesting a symmetrical avoidance. Rodent abundance was
associated with an increase in the probability of colonizing carrion for
both species. For Arctic foxes, however, this increase was only observed
in carcasses unoccupied by red foxes, showing greater avoidance when
alternative preys are available. Contrary to expectations, we did not
find strong signs of asymmetric competition for carrion in winter. Our
results suggest that interactions for resources at a short time scale
are not necessarily aligned with interactions at the scale of the
population. In addition, we found that competition for carcasses depends
on the availability of other resources, suggesting that interactions
between predators depend on the ecological context.