84 BRITISH BIRDS. [vol. vn. 



in its sexual life also. Apart from the general question of 

 fitness which this struggle implies — ^fitness not only physical 

 but psychical, as expressed in the disposition to secure as 

 well as to defend — we can see in many cases that this territorial 

 instinct is beneficial : in the smaller species for instance, 

 where an adequate supply of food is ensured for the helpless 

 offspring, or in cliff-breeding species where without a small 

 ledge or position on a ledge, reproduction would be impossible. 

 But in the case of a bird with such peculiar instincts as the 

 Cuckoo, it is not easy to indicate the precise direction in which 

 an advantage lies. It seems to me, however, that it may be 

 of use indirectly as a means of preventing the risk of the female 

 depositing more than one egg in the same nest. Why she does 

 not do so, why she does not repeat a profitable piece of 

 experience, has always been a mystery to me ; for it must 

 be manifest to anyone who studies the behaviour of the lower 

 animals, how strong a tendency exists towards repetition. 

 Some piece of behaviour, trifling perhaps in itself, is repeated 

 day after day under similar circumstances. Observe the 

 daily routine of any bird — ^notice the manner in which the 

 same tree, the same twig in fact, is made use of for a certain 

 purpose, the same spot resorted to for food or for the collecting 

 of nesting -material, the same lines of flight taken — and it 

 will be apparent how important a role association plays in 

 the psychology of birds. Now, the Cuckoo finds, with how 

 much effort we cannot say, a nest wherein to deposit her egg. 

 Having passed through this profitable and pleasurable piece 

 of experience, is it unreasonable to suppose that, if she remained 

 in the same locality and were again called upon to deal \\dth 

 her egg, the experience of the previous occasion would be 

 chosen for repetition. I do not think so, judging from the 

 behaviour of other species. How then is this risk averted ? 

 The females are said by competent observers to be polyan- 

 drous, and my own experience tends to confirm this view ; 

 the males are in excess and the females — are nomads wandering 

 from territory to territory, though perhaps only within 

 a certain radius. I have indeed been much impressed with 

 the fact that the males, though collecting round the first 

 female that arrives, and following her temporarily beyond 

 the confines of their territories, yet seem loth later to desert 

 their territories even though she passes through and is clearly 

 in sight. So that in the combination of these two facts, that 

 is to say polyandry and the law of breeding-territory, we 

 have, I believe, an efficient safeguard ; for if there were 

 no law of territory a number of males would follow 



