I smell a rat: Can New Zealand birds recognize the odor of an invasive mammalian predator?

Abstract

Abstract Although it is well known that birds can assess predation risk through visual and auditory cues, there has been little research into whether similar processes occur with olfactory cues. We examined the role of odor cues in assessing nest predation risk in four species of passerine birds in New Zealand. We compared the ability of two introduced European species (common starling Sturnus vulgaris and song thrush Turdus philomelos) and two native New Zealand species (rifleman Acanthisitta chloris and South Island robin Petroica australis) to respond to the scent of rat urine placed in the nest. Rats are an introduced predator in New Zealand and we expected the native birds, which did not co-evolve with any mammalian predators, to lack behavioral adaptations to the scent of rats at their nest. As expected, both riflemen and robins failed to show any change in their behavior at their nest when rat urine was present compared to a control period in which no scent was present. However, a similar lack of response was observed in the introduced song thrush; only the common starling changed its behavior in the presence of the rat urine. Starlings with rat urine at the nest box were more likely to hesitate before entering and they also approached the nest, but refused to enter more often in the presence of rat scent. Both responses suggest they detected the presence of a predator and changed their behavior to minimize risk to themselves. Although based on a small number of species, our results suggest that responses to predator scent may be less common in New Zealand species, and may be a factor contributing to the vulnerability of native birds to introduced mammalian predators.