THE ZOOLOGIST 



No. 890.— August 15th, 1915, 



THE RELATION OF THE OYSTERCATCHER TO ITS 

 NATURAL ENVIRONMENT. 



By J. M. Dewar, M.D. 



I. — Introduction. 



The effective relation of an animal to its environment largely 

 depends upon characters that are structural, physiological, and 

 psychological. The more specialized these characters are, the 

 more rigidly limited is the nature of the environment to which 

 the animal is able to respond. The Oystercatcher is structurally 

 specialized for a particular mode of feeding. Physiologically, it 

 appears to need large quantities of bulky, soft food, such as 

 shell-fish in winter, large earthworms and larvae inland in 

 summer, as it does not remain long in localities where these are 

 not available. Psychologically, the individual behaviour is 

 mostly stereotyped, and there is little evidence, short of the 

 experimental, of any capacity for adjustment to environments 

 which do not fulfil the special conditions of existence. Speciali- 

 zation secures the Oystercatcher from active competition with 

 neighbouring forms, especially for food, but it necessarily results 

 in the distribution of the species being discontinuous and depen- 

 dent upon the simultaneous recurrence of complex and little 

 variable environmental conditions. 



1. Areas under Observation and Method of Inquiry. — The pre- 

 sent communication reports the results of enquiries made on the 

 south shore of the Firth of Forth during the winters 1906-1914 in- 

 clusive ; on Loch Tummel, the lower portion of the River Tummel, 



Zool. 4th ser. vol. XIX., August, 1915. z 



