Temporal resource partitioning of wildebeest carcasses by scavengers after riverine mass mortality events

Abstract

Scavengers play an important role in nutrient recycling and disease control, and this role may be particularly critical after mass mortality events, such as those caused by epidemics, culling, or natural disasters. Current work on scavenger ecology has focused on use of single carcasses, but behaviors are likely to be different at mass mortality events, in which high resource abundance can prolong the spatial and temporal availability of carcasses. Little is currently known about how scavengers respond to large die-offs and understanding scavenger use and succession patterns at mass mortality events has important implications for disease ecology. We used photographic time series and river-side surveys of scavengers using carcasses to investigate scavenger use and succession on wildebeest carcasses that resulted from annual mass drownings in the Mara River, Kenya. In addition, we used telemetry data for tagged avian scavengers to assess individual use of mass drownings. Density of avian scavengers per carcass was almost two orders of magnitude lower at mass drownings than has been documented previously for single carcasses on land. Scavengers demonstrated patterns of temporal resource partitioning, with large-bodied avian scavengers more common initially, followed by small-bodied avian scavengers, and then by insectivorous birds and non-avian scavengers. Avian scavengers also differed in daily activity patterns, with marabou storks more common in the morning and late afternoon and white-backed and Rüppell’s vultures more common mid-day. Telemetry data indicated that approximately half of tagged vultures used mass drowning events but only spent a small proportion of their time there, suggesting that competition still plays an important role in scavenger dynamics at mass mortality events and that the rewards of such abundant resources may be offset by the risk of foraging in the river. Further research on scavenger behavior during mass mortality events is needed to better understand the role of scavengers in decomposition of carcasses and disease control during these events.