180 FRANCIS H. HERRICK 



on a small island inhabited by man (for Matinicus possesses a 

 lighthouse), than in more secluded places. (See section 5.) 



In considering the " perfection " of the nest we cannot over- 

 look the fact that the mutual attunement, or synchronization 

 of the instincts of any mated pair may in any case count for 

 much. Thus, Craig, '^ who has emphasized the importance of 

 this condition, has shown that in pigeons, the serial reflexes 

 of the reproductive period, to produce the best results, not only 

 must be attuned in the individual, but must be synchronized 

 in the pair; male and female act as a unit, by a process of mutual 

 adjustment or social control, now with impelling, and now with 

 inhibitory effect, based on suggestion; whenever this mutual 

 stimulus and response are ineffective, or when the male and 

 female " chronometers " are dissynchronous, the pair are ill 

 mated, and the results of the union are deficient or abortive. 



We shall see in a later section that as a rule both sexes play 

 a complementary part in nest-building, and that while the role 

 of the female is mainly constructive, that of the male is more 

 variable, but with a few possible exceptions at present known, 

 equally necessary. In the American robin, to use a familiar 

 instance w^hich is probably repeated in hundreds of its order, 

 the male builds but sporadically, his chief part being that of 

 guardian and incentor to action. Thus, in such a case, the 

 character of any given nest would seem to be determined not 

 only by the specific type molded by heredity, by all the influ- 

 ences of the environment including that of the weather, and the 

 factor of experience, embracing whatever adaptive intelligence may 

 be available, but by the mutual reactions of the builders them- 

 selves. The male robin, though he bring not a stick or a straw 

 to the nest site, by his pugnacity, his stimulating ardor or lack 

 ■or it, may effect or even control certain characters of the nest. 



3. THE CLASSIFICATION OF BIRDS' NESTS 



We now propose to examine the nests of birds in order to 

 ascertain what is essential to general and specific types of struc- 

 ture, and what significance variations from such types possess. 

 Upon this subject no little misunderstanding has arisen; but 

 this is in a measure inevitable, since the nests of wild birds are 

 commonly examined and described as finished structures, with 



"Craig, Wallace: Op. cit., p. 95. 





I 



