Conditioned food aversion reduces crow nest predation: An improved framework for CFA trials

Abstract

The decline of numerous bird species worldwide has been attributed to increased nest predation pressure often associated with anthropogenic factors. Identifying effective management strategies to reduce nest predation is therefore a conservation priority, but tests of management strategies often lack appropriate control treatments. Conditioned Food Aversion (CFA) is a non-lethal method of predator control where distasteful or illness-inducing artificial eggs are used to deliberately deter predators from nests or eggs of vulnerable prey species. Here, we test whether CFA can reduce predation pressure by pied crow on nests using an improved experimental methodology that includes spatial and temporal controls, non-rewarding control egg treatment and concurrent predator monitoring. At the Berg River Estuary, South Africa, we monitored survival of artificial plover-type nests and predator abundance in six sites across three experimental phases (pre-treatment, treatment and post-treatment). During the treatment phase, sites received either illness-inducing (carbachol-treated) or control (water-filled) quail eggs. Our results show that artificial nests survived longer after carbachol treatment in the post-treatment phase, both when compared to the pre-treatment phase and to the control treatment. Nest cameras revealed that pied crow were responsible for nest predation and point counts demonstrated that crow abundance did not change during the study period in control or treatment sites. Together, our results indicate that carbachol treatment induces CFA and reduces artificial nest predation by pied crow, and that mechanistically CFA in crows is likely driven by learning. This study demonstrates the potential for CFA to reduce nest predation and identifies a rigorous methodology for CFA trials.