44 BRITISH BIRDS. [vol. viiiJ 



The efficient causes of separation between bird-groups iuj 

 this country are less geographical than ecological ; the specific! 

 environment is the true " faunal-area." The group of J 

 species attached to a specific habitat compose an association,' 

 the units of AA'hich are primarily inter-related through the 

 comiecting-link of a common environment. The manner 

 of dispersal within the association is affected in varying 

 degrees by the inter-relations of the associates. Otherwise, 

 it is ruled by the quantitative relation between food-supply 

 and nesting -groimd. A localisation of the latter, together 

 with a relatively wide-spread or abmidant food-supply, is 

 one factor leading to^^■ards social nesting. 



The aims of the bird-ecologist in this coimtry might be in 

 some degree summed up as : firstly, by working baclcAvards 

 from analysis of the remaining representatives of primitive 

 ground, to reconstruct the original aspect of the avifaima ; 

 to follo\\' the faimal changes induced by the direct and 

 indirect influence of man ; and to trace the genetic relation 

 between the avifaunas of "natural" and "artificial" 

 areas ; and secondly, to reach through statistical method and 

 comparison a valuation of present structural and functional 

 environmental links and factors. 



In botany the ecological method has already justified itself. 

 If it be sound in botany it must be equally applicable to 

 zoology. Analysis of the environmental control is, in fact, 

 an indispensable aid towards a full conception of the 

 phenomena and causes of geographical distribution. That 

 in birds the problems are exceptionally intricate should only 

 serve to render the subject the more attractive. 



