ECOLOGY OF ISLE ROYALE. 151 



It is not at all unlikely that succession is very closely related to some 

 of the causes of bird migration, and that witli advance in this subject 

 much light would be thrown upon migration. Migration is doubt- 

 less another illustration of convergent phenomena. In all probability, 

 migration has originated not only independently in very diverse kinds 

 of birds, but perhaps repeatedly, from, different causes, even in the 

 same group. The causes of migration must be numerous, varying with 

 different ecological groups, which appear to be the true natural units 

 for study and comparison. Thus the comparative study of migrations 

 of different kinds of associations, as formations and societies, should 

 lead not only to a better understanding of the various associations, but 

 should also contribute to the general subject of migi*ation which seems 

 to have shown a tendency toward stability in the current methods of 

 study. It scarcely seems probable that with the diverse formations in- 

 habited by birds, and with their ecological diversities there should be 

 only a few causes of the phenomena. 



To keep pace with successions animals must either adjust themselves, 

 change their habitat, or migrate. From such relations it is evident that 

 various supposed environmental responses must be tested primarily 

 'ifithin the association and enviroiiment to ichich the animal normaUif 

 helongs. To this class belongs protective coloration and allied phenom- 

 ena. To be of fundamental value, the influence must have some perman- 

 ence and this may be sought in the dynamic trend and dominant influ- 

 ences of different associations. It is diiiScult to conceive of other more 

 reliable methods of approach to such problems. 



In addition to the scientific value of this line of investigation, there 

 are important economic applications of the laws of avian environment. 

 This is particularly true of forestry and agriculture. The forestry prob- 

 lem is continually becoming more important, but the relation of bird 

 life to forests and forest succession has received little attention. As 

 agents for scattering seeds of trees and shrubs, birds are very important. 

 Here is where the interests of the avian ecologist and forest ecologist 

 overlap. The student of bird life will wish to know how a region is to be 

 reforested, and what succession of bird life will attend the succession 

 of the forest as refoi'estation progresses. On the other hand, the 

 forester will wish to know how birds will aid or retard him in the 

 process of reforestation. Then, in guarding or protecting the forest, 

 what help can be secured from birds with regard to insect pests? These 

 are only samples to show that here is a. field which, as time advances, 

 will become of more and more importance, and that these problems 

 will eventually call for specially trained men to handle them. 



In- connection with forestry and agriculture we have quite exceptional 

 conditions for extended experimental studies in bird succession as re- 

 lated to forest succession, crop rotation, etc. The relation of birds 

 to agriculture appeals to .a much larger number of people than does 

 their relation to forestry. There are several reasons for this ; first, 

 because more persons are interested in farm and horticultural crops 

 than in forests; and second, because birds are soon attracted in such 

 large numbers by the food supply of grains and fruits which these crops 

 so greatly increase, that the extensive destruction, by birds readily at- 

 tracts attention. And while we hear much of the great reduction of 



