XVII 



BIRD BEHAVIOUR 



1 . Habitat selection 



The success of bird life has been largely due to the great variety and 

 ingenuity displayed in finding situations suitable for providing food 

 and allowing reproduction. Their powers of habitat selection allow 

 diversification of species by reducing interspecific competition. Species 

 living in the same area rarely eat the same food, especially if it is 

 scarce. It is often said that birds are creatures of stereotyped habits, 

 yet they have certainly exploited their mobility to the full; they obtain 

 the means of life in most various ways. This mobility makes it difficult 

 to specify the 'environment' of a bird. For instance, a swallow may 

 pass part of its life in the tropics, part near the Arctic Circle. A gull 

 may nest on a rock, eat grain in a field, and then fish in the sea, all 

 within a few hours. Observation of the familiar birds of town and 

 country soon shows that they are at home in a much greater variety 

 of situations than could be supported by most animals, and that within 

 limits they can adapt their behaviour to each situation. Birds show, 

 therefore, in a marked degree, two of the features most commonly used 

 as criteria for the recognition of a higher animal, namely, freedom to 

 move to different conditions and ability to obtain a living in unpromis- 

 ing circumstances. 



Nevertheless each species nests in a limited variety of habitats and 

 feeds in a limited variety of habitats. There is evidence that the 

 appropriate habitat is recognized by a relatively small number of 

 conspicuous features, independently of learning. 



2. Food selection 



Where the food is very specific substitutes will only be accepted 

 under unusual conditions of starvation, but many birds are more 

 catholic in tastes and some of these are among the most common, for 

 instance rooks, starlings, thrushes, blackbirds, and gulls. Both field 

 observation and experiment suggest that birds quickly learn from 

 experience where and how food may be obtained. They will remember 

 to visit an abundant source of supply and there are numerous stories 

 of the ingenuity of such birds as the jackdaws in obtaining it. This 

 short-term memory is probably of great importance in allowing the 



