Spatio-temporal variation in small carcass use in urban and rural areas: the effect of site characteristics and predictability

Anthropogenic installations and human activities considerably increased in the last decades, and this trend led to an accumulating number of human caused animal threats, such as collisions with vehicles (road kills and train kills), glass panels, wind farms, intensive farming of agricultural land and non-fed prey of domestic cats. The resulting carcasses are available to scavengers and can be an important food resource for scavenger communities worldwide. This study investigated the effects of detectability and predictability of small carcasses (mainly voles) on carrion consumption by facultative scavengers in the Swiss habitat gradient of rural to urban areas by performing a carcass placement experiment at day and night. 720 vole carcasses were provided and monitored by wildlife camera traps. 504 carcass placement experiments were conducted at 252 different locations, 252 at day and 252 at night. At 27 of these locations learning experiments were performed by four-day repetition of a carcass placement experiment at the same location (additional 216 carcass placements, half of them at night, half at day). The influence of vegetation height (detectability), road proximity (predictability) and weather variables on carrion consumption were examined.

Ten different facultative scavenger species removed 213 of 499 (43%) provided carcasses within less than twelve hours, whereas repeated carcass placement at the same location (learning experiments) resulted in 50% carcass removal (108 out of 216). The most common scavengers were red foxes (Vulpes vulpes), domestic cats (Felis catus), Carrion crows (Corvus corone) and Eurasian Magpies (Pica pica). The scavenger community was considerably different between day and night and between urban and rural habitats. The results suggested that the carrion consumption was higher at night than at day, but did not differ between urban and rural habitats, suggesting that urban and rural scavenger communities do not differ in the performance of the ecological function of carcass removal. The carrion consumption was affected by vegetation height (detectability), carcass weight and wind. Repeated placement of carcasses at the same location (learning experiments) and short distances from roads, both situations of a high spatial predictability of carrion, increased the carrion consumption, suggesting a learning effect.

The results give insights into the complex ecosystem processes associated with the functionality of facultative scavengers communities removing predictable and unpredictable carrion resources in the habitat gradient of rural and urban areas.