Role of chemical and visual cues of mammalian predators in nest defense in birds

Abstract

We explore for the first time the relative importance of chemical and visual cues of predators in nest defense and antipredator behavior in a hole-nesting songbird, the blue tit Cyanistes caeruleus. Birds breeding in nest boxes were exposed to chemical or visual cues of a predatory and a non-predatory mammal during the nestling stage, and their behavior both outside and inside nest boxes was recorded with video films. Our results show that birds respond equally to chemical and to visual cues of predators in a context of nest defense. Adult birds minimized predation risk by decreasing the time spent inside the nest box while feeding nestlings when they were exposed to either visual or chemical cues of a mammalian predator. They decreased the time spent in non-essential activities for nestlings’ survival, such as nest sanitation activities, but they maintained provisioning rates so that the nestlings’ growth was not compromised. In this way, birds minimized the risk of predation while provisioning nestlings when a predator was detected in the vicinity of their nest. We explored the role of predator chemical and visual cues for risk assessment in blue tits. Our results showed for the first time that birds respond equally to chemical and to visual cues of mammalian predators. Birds decreased time exposed to predation risk when entering the nest box to feed the nestlings. They reduced time spent in non-essential activities for nestling survival, such as nest sanitation. However, they maintained provisioning rates so that nestling growth was not impaired.