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In several field observations, foxes, Spotted hyaenas and other carnivores killed many more prey individuals than they could eat. Functional and causal aspects of this phenomenon are discussed and the conclusion is reached that these surplus kills are the consequence of behavioural compromises in both predator and prey to meet opposing environmental requirements.

Summary:

(1) Observations are reported in which carnivores killed considerably more prey animals than they could possibly eat, and causal and functional aspects of this behaviour are discussed. The species concerned were especially foxes and Spotted hyaenas, and references are quoted about surplus killing by other Canidae, Felidae and Ursidae.

(2) It is argued that satiation in carnivores does not inhibit further catching and killing, but it probably does inhibit searching and hunting. Thus carnivores are able to procure an “easy prey” but normally satiation limits numbers killed.

(3) Many, if not all, carnivores possess behaviour patterns which allow utilization of a kill at a later time, or allow other members of the same social unit or offspring to use the food.

(4) Several prey species showed a lack of anti-predator reaction under particular climatological circumstances; it is argued that this lack of response usually has survival value. Sometimes anti-predator behaviour is accidentally made ineffective.

(5) Surplus kills are made possible by (2) and (4) above, and only very rare circumstances give a predator access to so many prey that (3) is ineffective. It is suggested that surplus kills are the consequence of behavioural compromises in both predator and prey to meet opposing environmental requirements.