Following the bear: The interspecific foraging associations between vertebrate predators of cicada nymphs

Abstract

Disturbance foraging, the behavior for obtaining food at a disturbance created by another organism, is a widespread form of commensalism interaction observed across the animal kingdom. In the Shiretoko World Heritage site in northern Japan, brown bears (Ursus arctos) dig for cicada nymphs, causing soil physical disturbance. Other predators of cicada nymphs may exploit the soil disturbances caused by brown bears to gain easier access to soil prey, including cicada nymphs. Here, I observed the foraging association among cicada nymph predators, especially brown bears, red foxes (Vulpes vulpes), and crows (Corvus macrorhynchos and C. corone) using camera traps. Notably, the camera traps captured 14 instances of crows and brown bears cooccurring, with the crows engaging in disturbance foraging. In contrast, foxes were never captured alongside brown bears. In addition, the interspecific foraging association between the crows and brown bears was more frequently observed before the cicada emergence season than during it. This suggests that crows predominantly engage in the interspecific foraging association with brown bear digging to facilitate easier predation on the soil-dwelling cicada nymphs prior to the cicada emergence season. During the emergence season, cicada nymphs emerge aboveground, and crows can easily prey upon them without the disturbance of the brown bear digging. The strength of the disturbance foraging association between brown bears and crows is affected by seasonal variations in the life history of prey.