THE PHENOMENON OF PREDATION — ERRINGTON 509 



predators may at times suffer from concerted canine predation — I have 

 known instances of this sort of thing in my studies of predation by 

 foxes and dogs upon muskrats and ground-nesting birds. 



But, modern studies on predation by lower vertebrates have demon- 

 strated that learning can have a pronounced influence on their food 

 habits. Fishes learn to take certain food items. Frogs may prey 

 selectively through experience. Also, in late years, I have been gain- 

 ing an impression from various sources that some insects and other 

 active invertebrates may have capabilities for more individual pref- 

 erences than we commonly have thought. A morphologically ad- 

 vanced brain is not an absolute prerequisite to a psychology of learn- 

 ing and choice. 



PSYCHOLOGICAL ASPECTS 



Let us consider some of the ways that predation may be influenced by 

 the psychology of either or both predators and their prospective prey — 

 not forgetting that predators may generally take such prey as is 

 easiest for them to get, suitable for their requirements, and recognized 

 as food. 



Some of the clearest examples of psychological influence in pred- 

 ator-prey relations are those in which adversaries do a good deal of 

 testing out and appraising each other's intentions and capabilities. 

 The caution that predators show toward dangerous prey may be 

 illustrated by wolves sizing up their prospects for attacking moose, 

 bison, or muskoxen, or by the behavior of minks in the presence of 

 formidable muskrats ; but a predator's decision to attack or not attack 

 may be quite unrelated to any threat of danger to the predators, them- 

 selves. Wolves also appraise their chances with caribou that they 

 have no reason to fear. Bird-hunting hawks may repeatedly test by 

 preliminaiy feints the attitudes of small birds that could not possibly 

 do more than to escape. 



Prospective prey that displays alertness toward predatory dangers 

 yet conducts itself in a recognizably confident manner may discourage 

 predators from attacking or cause the predators to desist soon after 

 an attack is undertaken. I think we should give many predatory 

 vertebrates credit for knowing pretty well when a serious attempt is 

 not worth going through with. Conversely, except for manifest in- 

 juries or helplessness, panic on the part of the prey may encourage 

 attacks about as much as anything. 



There may be, however, a still weightier psychological factor in 

 some predator-prey relationships: social intolerance. 



One aspect of social intolerance — territoriality, or the defense of an 

 area — has been best studied in mammals and birds, in some lower 

 vertebrates, and in a relatively few invertebrates. Even among the 

 mammals and birds for which it represents most nearly characteristic 

 behavior, territoriality may exist in virtually all conceivable degrees 



