268 BIRD BEHAVIOUR 



for the fact that the comparatively very stupid 

 Pigeons, with much the same general distribution 

 and diet, have nevertheless on the whole a wider 

 range and greater success in the struggle for exist- 

 ence, since they can at any rate construct their own 

 cradles, and do not usually depend on hoks, found 

 or dug out, for a breeding-place, as Parrots do. 



The association between general intelligence and 

 strength of character and the hole-breeding habit is 

 often very marked, occurring in Parrots, Starlings, 

 Tits, and Sheldrakes, for instance, but as it limits the 

 breeding potentialities of birds, it must be regarded 

 as either degeneracy or a blind retention of ancestral 

 custom, as compared with the nest-constructing 

 instinct, and is no doubt favoured by the fitness 

 in other directions of the birds which practise it. 

 It is probably the great and general development 

 of the nest-constructing instinct in the Passerines 

 which accounts largely for the success of these 

 birds, since in general intelligence and strength 

 of constitution they do not seem superior to many 

 other groups. 



A very large field of observation is presented by 

 the phenomena of expression of emotion in birds, 

 and it is intimately related to the study of bird 

 courtship ; for it is a very important point to 

 notice that the so-called courting pose is often 

 exactly that which is assumed under any emotions 

 such as anger and even fear, and that it is frequently 

 displayed by the hen equally with the cock. 



Thus, to take a well-known instance, the Turkey- 



