Dietary Overlap of Sympatric Terrestrial Mammalian Carnivores within Coastal Impoundments of South Carolina

Abstract

Coastal ecotones, where marine aquatic and terrestrial habitats interact, are productive systems that often contain abundant and diverse assemblages of invertebrate and vertebrate species and their predators. The availability of allochthonous inputs in combination with resident prey items within tidal marshes could lead to heightened density of terrestrial predators, although research into the ecology of coastal terrestrial predators is sparse. Given the use of coastal impoundments by culturally and economically important waterfowl, some managers are (or are considering) lethally removing terrestrial mammalian carnivores out of concern they are consuming waterfowl species during the overwintering and spring recruitment periods. We conducted a study to determine terrestrial carnivore diets within tidal impoundments in South Carolina during the 2018-2019 winter and spring seasons and compared dietary breadth and overlap among predators. We determined that Lynx rufus (Bobcat) and Procyon lotor (Raccoon), and, to a lesser extent, Canis latrans (Coyote) used coastal impoundments and consumed a diversity of food items that varied between seasons. Bobcat diet was primarily composed of small-to medium-sized mammalian prey, the relative frequency of occurrence of those items being 77% and 65% of scats during winter and spring respectively. The relative frequency of birds in Bobcat diet was higher in spring (32%) compared to winter (18%), with a majority being composed of songbirds and waterbirds, and waterfowl only accounting for 6% of their diet across both seasons. Raccoon diets were primarily composed of vegetation and crustaceans, 2 items not consumed by Bobcats, suggesting the 2 species generally maintain different dietary niches. Small mammals were the only dietary item of potential overlap between these species, but Bobcats were more likely to consume meso-mammals in winter while Raccoons were more likely to consume small mammals in spring. In addition to providing support for dietary niche partitioning as a coexistence mechanism for Bobcats and Racoons in our system, our results suggest that Bobcats (as well as Raccoons) are not predating important waterfowl species within these managed impoundments during these seasons, likely limiting the need for future lethal predator-control strategies.