Predator chases by breeding waders: interspecific comparison of three species nesting in Iceland

Parents defend their offspring from avian predators by distracting them with diversionary displays or drive them away by aggressive mobbing. The intensity of such defence can vary with the hazard that any given predator represents but also with characteristics of the mobber species. Decision making of parents in responding to different predators has potentially great fitness implications. We studied the responses of differently sized waders to different avian predators in south Iceland during 2001–2003. We collected data on intrusions, which we defined as the appearance of a predator within our study site. We compared mobber species with respect to  location and predator (species, flight pattern and flight altitude). The most commonly observed mobbers were Black-tailed Godwit Limosa limosa, Whimbrel Numenius phaeopus and Redshank Tringa totanus, which performed 89.4% of all mobbing events. Four predators were the most commonly observed (93% of all intrusions), Common Raven Corvus corax, Arctic Skua Stercorarius parasiticus, Lesser Black-backed Gull Larus fuscus and Great Black-backed Gull L. marinus. Godwits and Whimbrels responded to the different predators with varying intensity but Redshanks responded similarly to the four predator species. We suggest that the size of predators and mobbers influences mobbing intensity in waders through mobber risk perception. Parental  investment at different stages of the breeding season must take into account the differing presences of predators and will be dependent on predator breeding schedules.