^°1908^^] Adams, Ecological Succession of Birds. 141 



land, orchartl, swamp or meadow, whieli tl^e male is ever on the 

 alert to defend against trespassers of his own kind and sex, althouglji 

 he often seems quite willing to share his domain with birds of other 

 and perhaps closely related species. The extent of the area thus 

 monopolized varies exceedingly with birds of different species. 

 An apple orchard which affords sufficient room for — let us say — 

 two pairs of Yellow Warblers, two pairs of Orioles, three or four 

 pairs of Chippies and four or five pairs of Robins, seldom or never 

 harbors more than a single pair of Kingbirds or Crested Flycatchers 

 .... As a rule, the species which roam over the most ground in the 

 course of their daily wanderings claim and maintain the broadest 

 preserves, while those of sedentary habits often content themselves 

 with very modest freeholds. Whatever the extent of the domain, 

 the birds who occupy it as a summer home cAndently regard it as 

 exclusively their own. The readiness and celerity with which 

 trespassing birds are accustomed to retire when attacked or even 

 merely threatened by the established tenants, has seemed to me to 

 indicate that the claims of temporary ownership are respected 

 by all right-minded birds .... In my opinion the desire for exclusive 

 possession so conspicuously shown by the male, and often by him 

 alone, is usually the direct result of sexual jealoxisy. This, as is 

 natural, makes him intolerant, during the breeding season, of the 

 near presence of rival males. If his concern were chiefly in respect 

 to the food supply, it would be equally manifested at every season 

 and towards all birds wlio subsist on the same food that he and his 

 mate require — which is certainly not the case." 



The tendency or pairs and species to space ihemselves and to 

 become relatively sedentary is thus a characteristic condition in an 

 association, and is an important element in an understanding of 

 succession because it shows the internal organization and habit 

 with which an invader or pioneer from another association has to 

 contend. As Dixon ('97, p. 91) has pointed out, this spacing tend- 

 ency is an important factor in the extension of range of species and 

 is intimately related to the location of nesting sites. These facts 

 clearly show that both these internal influences and the environ- 

 mental ones must be distinguished if w^e wish to determine the rela- 

 tive influence of each and their bearing on succession. The above 

 quotation from Brewster clearly shows that in general not only a 



