Mammalian nest predator feces as a cue in avian habitat selection decisions

Breeding habitat selection is expected to be adaptive. Animals should respond to strong agents of natural selection, such as expected offspring mortality due to nest predators, in their settlement decisions. In birds, mammalian nest predators are a significant mortality source and birds are known to respond to their presence. However, the mechanism used by birds to perceive mammalian nest predators and estimate the nest predation risk remains unknown, in particular at larger spatial scales while comparing potential breeding habitat patches. We experimentally tested whether the farmland bird community can detect and perceive cues of a mammalian nest predator (urine and feces), and how this perception affected the habitat selection and community structure of birds. The experiment was conducted at a large habitat patch scale by simulating a high abundance of nest predator by spraying on the ground water with dissolved mink excrements, whereas water was sprayed in the control treatment. Birds avoided settling in the plots treated with nest predator excrement. The number of migratory passerine species and their total density were lower in the simulated predation risk treatment than in the control treatment. Our results revealed a novel antipredator behavioral mechanism in birds; passerine birds can detect the excrements of mammalian nest predators and thereby assess the relative nest predation risk among potential breeding habitat patches. This mechanism has direct impacts on the structure of avian breeding bird community.