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Does an opportunistic predator preferentially attack nonvigilant prey?
Stockholm University, Faculty of Science, Department of Zoology.
Stockholm University, Faculty of Science, Department of Zoology.
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2003 (English)In: Animal Behaviour, ISSN 0003-3472, E-ISSN 1095-8282, Vol. 66, no 4, 643-648 p.Article in journal (Refereed) Published
Abstract [en]

The dilution effect as an antipredation behaviour is the main theoretical reason for grouping in animals and states that all individuals in a group have an equal risk of being predated if equally spaced from each other and the predator. Stalking predators, however, increase their chance of attack success by preferentially targeting nonvigilant individuals, potentially making relative vigilance rates in a group relatively important in determining predation compared with the dilution effect. Many predators, however, attack opportunistically without stalking, when targeting of nonvigilant individuals may be less likely, so that the dilution effect will then be a relatively more important antipredation reason for grouping. We tested whether an opportunistically hunting predator, the sparrowhawk, Accipiter nisus, preferentially attacked vigilant or feeding prey models presented in pairs. We found that sparrowhawks attacked vigilant and feeding mounts at similar frequencies. Our results suggest that individuals should prioritize maximizing group size or individual vigilance dependent on the type of predator from which they are at risk. When the most likely predator is a stalker, individuals should aim to have the highest vigilance levels in a group, and there may be relatively little selective advantage to being in the largest group. In contrast, if the most likely predator is an opportunist, then individuals should simply aim to be in the largest group and can also spend more time foraging without compromising predation risk. For most natural systems this will mean a trade-off between the two strategies dependent on the frequency of attack of each predator type.

Place, publisher, year, edition, pages
2003. Vol. 66, no 4, 643-648 p.
National Category
URN: urn:nbn:se:su:diva-24588DOI: 10.1006/anbe.2003.2233OAI: diva2:197843
Available from: 2005-11-02 Created: 2005-11-02 Last updated: 2014-10-28Bibliographically approved
In thesis
1. Attacking predators and fleeing prey: detection, escape and targeting behaviour in birds
Open this publication in new window or tab >>Attacking predators and fleeing prey: detection, escape and targeting behaviour in birds
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The aim of this thesis is to further our understanding of predator and prey behaviour and decision making in different attack situations. The thesis deals with escape strategies, predator detection ability and prey targeting behaviour. Thus the thesis includes several aspects of a predation event and it includes studies both on prey animals and predators. In the first paper we show that blue tits (Parus caeruleus), a small passerine bird, are highly flexible in their escape behaviour and adjust their escape to the detailed behaviour of an attacking predator. The predator’s attack height influenced the blue tits’ ascent angles whereas attack speed influenced the lateral course of the flight. These escape responses might reflect a turning gambit between prey and predator. To adjust escape behaviour might therefore be very important for survival. Our result from the second paper suggests that the evolution of flexible escape behaviour is influenced by habitat and life style. We found that open living bird species adjusted their escape behaviour to the behaviour of a predator to a higher degree than skulky, cover living bird species did. The third paper deals with how different aspects of foraging influence blue tits’ ability to detect predators and time till take-off. Detection ability in prey can heavily affect their likelihood to escape successfully. The body posture of the blue tits (head-up or head-down) did not affect their detection ability whereas their orientation did; detection was delayed when the attack came from behind. Foraging behaviour is often assumed to delay predator detection but we could not find any negative effect of an easy foraging task. A difficult task, on the other hand, severely delayed detection of the predator and time to take-off. In the last paper we investigate if sparrowhawks (Accipiter nisus) hunting opportunistically can discriminate between prey birds on the basis of vigilance state and preferentially target foraging birds for attack. The sparrowhawks showed no preference for foraging prey which is in contrast to predators which inspect their prey before attack. Thus our results suggest that predators may only have time to discriminate between individuals on the basis of vigilance state when stalking.

Place, publisher, year, edition, pages
Stockholm: Zoologiska institutionen, 2005
zoology, ethology, birds, animal behaviour
urn:nbn:se:su:diva-720 (URN)91-7155-135-2 (ISBN)
Public defence
2005-12-16, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 8 C, Stockholm, 10:00
Available from: 2005-11-02 Created: 2005-11-02Bibliographically approved

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Lind, JohanJakobsson, Sven
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