The Effects of Predation Risk and Group Size On the Anti-Predator Responses of Nesting Lapwings Vanellusvanellus

The anti-predator responses of nesting lapwings were studied near Newburgh, Aberdeenshire, Scotland, using taxidermy mounts of a carrion crow, great black-backed gull, and red fox pulled towards their nests. Lapwings appeared to respond to these dummies and to a control woodpigeon as they would to the live animals. Responses to nest predators that are relatively harmless to adult lapwings, represented by the crow, included initial investigative flights. These quickly changed to diving attacks, over 60% of which actually struck the dummy predator. In response to the fox, which is a threat to both the adults and the eggs, lapwings never made physical contact, but circled overhead, or attempted to lead or distract the predator on the ground. Responses to the fox were similar in daylight and darkness, but lapwings did not respond to the dummy crow at night. Both diving and distraction responses to the gull were observed. Thus the closeness of attack was inversely related to the risk that the live predator would have posed to the adults. The intensity of response to the dummy crow increased through the incubation period and breeding season, as predicted on the basis of a decreasing difference between the reproductive value of the adults and the clutch they were protecting, resulting in the defenders under-taking increasingly greater risks. Both the number of lapwings responding to the crow, and the distances from the nest at which high intensity responses occurred, increased with the size of the nesting aggregation, ranging from one to five pairs, but not with the number of birds present prior to the experiment. Both these effects should lead to a higher probability of successfully repelling a crow with increasing group size. The area in which diving attacks occurred extended to 40-60 m from the nest in larger groups. Neither relationship was found in experiments with the dummy fox, in which all high intensity responses were performed by one adult only. Nesting in loose aggregations thus seems to enhance the effectiveness of the lapwings' responses to nest predators such as crows, but not to more dangerous predators such as the fox.