60 BRAIN MECHANISMS AND LEARNING 



actually lies. Such a complex behaviour pattern as prey hunting is, of 

 course, not fully innate or learned as a whole, and we agree with Kuo that 

 to pose such an alternative is a mistake. But, like Riess, Kuo did not see 

 that the complex functional unit in any animal's behaviour is formed by a 

 number of smaller behavioural patterns. In his paper, no single, particulate 

 behaviour pattern is described. We investigated the prey-hunting be- 

 haviour of the polecat, asking it there were any fixed motor patterns or 

 innate orientation movements involved in the pattern, and if so where and 

 how experience enters. 



Every adult polecat kills rodents which are able to defend themselves, by 

 biting them in the neck or occipital region. Prey in flight is often grasped 

 {{^raspiii'^) on another part of the body, but after the polecat has thus 

 stopped the prey's flight, it immediately releases its preliminary hold to 

 grasp the neck. Often it turns the prey on its back and shakes it torcetully 

 {shakiiii^), in the way employed by many other carnivorous animals. The 

 polecat furthermore loosens and fastens its grip, in rapid succession, sinking 

 its teeth repeatedly in exactly the same spot, thus gradually perforating 

 the skull {hillino hitc) (Eibl-Eibesfeldt, 1956a). 



Studying the ontogeny of this technique in non-deprived animals, one 

 finds that they show little skill in their first attempts to kill a prey, prob- 

 ably partly due to the lack of bodily strength. At the age of 3 months, 

 however, a polecat is a skilful killer. 



Twenty polecats were raised under deprivation. They were not con- 

 fronted with living prey until the test, but were fed with meat and even 

 dead rats to keep them in a good state of health. Eight of the polecats 

 remained with their mother and litter mates. Twelve were isolated at the 

 age of 21 days from members of their own species. Six of the polecats 

 raised in isolation and eight of those raised with their litter mates, but also 

 never being confronted with living prey, were given an adult rat when 

 they were 5 months old. One of those raised in isolation was tested at 10 

 months, and five raised in isolation were 2 years old when first given a 

 prey. The latter were given chicks. 



Those tested at the age of 5 months behaved as follows. It the rat 

 remained motionless on the spot, the polecat approached slowly, sniflmg 

 with curiosity at the prey and touching it with the paws. Some licked or 

 carefully tried to bite, but they did not attack. If the rat ran towards the 

 polecat, the latter retreated. But as soon as the rat showed flight reactions 

 by running away, the polecat attacked it vigorously, trying to grasp and 

 bite it. It did not direct its attack towards a special part of the rat's body, as 

 an experienced polecat does, but just bit into what it grasped, the tail, the 



