Hyperpredation of Freshwater Turtles and Tortoises by Subsidized Corvids

Abstract

Subsidized predators are animals whose populations proliferate through association with humans. As subsidized predators, birds in the family Corvidae (Corvus spp., crows and ravens) pose an additive mortality threat to turtle eggs, juveniles, and, in some cases, adults. In this synthesis, I (1) review published and unpublished case studies of corvids as predators of chelonians, (2) examine regional population trends of corvids relative to the status of co-occurring chelonian species, and (3) evaluate our current understanding of subsidized corvids as threats to chelonians. Hyperpredation of chelonians by corvids is geographically widespread, locally severe where and when predation occurs, facilitated by anthropogenic subsidies (e.g., food, water, and perching, nesting, and roosting sites) and linear corridors (e.g., roads, electrical infrastructure), commonly associated with nesting corvids as predators, and co-occurring with corvid population increases. Hyperpredation by corvids appears to affect demographically sensitive stages of chelonian populations (juveniles and reproductive females) and very likely has long-term detrimental consequences given the slow life history of chelonians. The threat posed to chelonian populations by subsidized corvids is more widespread than currently recognized on the basis of substantial regional increases in corvid populations, the underreporting of predation observations, and the broad geographic areas over which hyperpredation of chelonians is occurring.