Predator odour recognition in Eurasian kestrels

Semiochemicals released by predators (i.e. “kairomones”) may be useful for prey species. Knowledge on functional use of olfaction to detect kairomones and the consequent antipredator behaviour remains scant in birds, especially in raptors. The study population of Eurasian kestrels Falco tinnunculus canariensis inhabits the island of Tenerife, and man is one of its main predators, destroying clutches and stealing nestlings. Man and kestrels have evolved in sympatry or, at least, have been sharing the habitat for a long time. Parent kestrels were exposed to chemical cues: human fresh urine (predator), cologne (odorous control), or water (odourless control) in the nest when provisioning for nestlings. They did not display clear signs of aggressive antipredator behaviour when in contact with kairomones released by a non-present human predator. With human urine, they visited less, arrived earlier the first time in the trial, but their refusal percentage dropped significantly, and they spent more time inside the nest than those containing cologne or water. Females, especially, visited those nests highest above the ground less times regardless of substance. Interactions among some environmental (e.g. nest height, variations in human urine odour) and behavioural factors (e.g. neophobic response) could influence kestrel behaviour regarding kairomones. Kestrels would exhibit commensurate responses according to the magnitude of predation risk faced. We suggest kestrels do not ultimately react through behavioural defence mechanisms based on chemical cues from human predators, although it remains unclear if they respond to these chemical cues in other ways.