Do invasive predators pose a predation risk to roosting shorebirds? Fecal DNA and camera trap analysis

Abstract

Shorebird populations have experienced dramatic population declines worldwide. Reasons for these declines are varied, but one largely understudied threat at migratory shorebird non-breeding grounds is predation by introduced predators. High-tide roosting shorebirds may be vulnerable to ground predation, as they roost in a spatially clumped and temporally predictable manner in areas easily accessible to ground predators. We measured predation risk by the introduced red fox (Vulpes vulpes) at high-tide roosts within 2 internationally important shorebird estuaries in New South Wales, Australia, during a time when non-breeding shorebird numbers were at their annual peak, using a combination of camera trapping and environmental DNA (eDNA). Foxes were present at all study sites and were seen most frequently at sites encompassing the 2 largest high-tide roosts within the study estuaries, and least frequently nearest the roosts. Metabarcoding identified a broad range of avian taxa in fox scats collected at roosts, including ground-dwelling birds, native waterbirds, and introduced pigeons and doves, but no shorebird species. Bird prevalence in fox scats reached levels that far exceeded those reported in prior studies. Future studies should examine whether red foxes present a non-lethal, rather than lethal, predation threat to high-tide roosting shorebirds when feeding on other co-occurring food sources, potentially inducing energetically costly predator avoidance.