Predator search image and the dilution effect: When is the best time to nest?

Abstract

AbstractThe predator search image hypothesis predicts that predators will focus on prey that are abundant and with which they have had success. However, the predator dilution effect hypothesis predicts a decrease in the per capita chance of being depredated with an increasing amount of prey. We evaluated these hypotheses through an artificial nest survival study. We estimated nest survival during both the non-breeding and breeding seasons of 2014 at a restinga (sand-coastalplain) area in southeastern Brazil. We installed 450 artificial nests (cup shaped) in each season and placed a Common quail (Coturnix coturnix) egg in each nest, totaling 900 nests. During the non-breeding season, our nests were the only ones present and thus the predator dilution effect should be absent. We estimated daily survival rate (DSR) using the “Nest Survival” function in the program MARK. We found a decrease in DSR at the middle and end in comparison with the onset of the non-breeding season, which supports the predator search image hypothesis. In comparison with the nonbreeding season, we also found that DSR of artificial nests was lower at the onset and end of the breeding season, but higher in the middle of the breeding season. This pattern matched the higher availability of prey (i.e. natural nests) in the middle of the breeding season in the study site, supporting the dilution effect hypothesis. The survival rate of artificial nests suggests that both the search image and the dilution effect may occur during the breeding season, and that the predator dilution effect masks the predator search image in the middle of the breeding season. Our results expand our understanding regarding the effects of the search image and predator dilution effect hypotheses on nest predation, showing that both are density-dependent and may occur during the breeding season