94 TROPICAL WILD LIFE IN BRITISH GUIANA 



army ants, it is quite unreasonable to attempt to explain 

 their daily movements by any controlling factor but that of 

 the chance of appeasing hunger and of the meteorologically 

 influenced dispersal of insects. But the search for food once 

 past, the life of the bird came under some more definite con- 

 trol again, and a succession of more or less predicable reac- 

 tions. These, I think, will be very worthy of study and tabu- 

 lation, as important factors in the evolution of the ever- 

 changing adaptations and readjustments, which have result- 

 ed in the complex of life as we find it in the jungle today.. 



In the case of a fixed, occupied nest, the range of the 

 owner often difl'ered from corresponding conditions in the 

 north, b}^ reason of tlie excessive altitudinal zones. Both 

 parents may have spent tlieir free time almost directly over- 

 head, and yet so high up as to have been almost unrecog- 

 nizable. I have sat and watched a nest for an hour without 

 seeing any trace of the bird until I happened to glance up- 

 ward where both were seen at once, revealed by their action, 

 identified with the high power stereo glasses. In the course 

 of extensive observation it will I tliink be possible in time 

 to plot certain daily, if not hourly habits — wanderings, court- 

 ship areas, feeding zones, points of lookout. Yet I do not 

 mean in any way to depreciate the free will and individual- 

 ity of birds, only that their lives, like those of ourselves, are 

 regulated by many factors, known and unknown, whose de- 

 tection will be useful to our great idterior purpose. The 

 home range points this belief. 



The daily migration may be taken as an excellent exam- 

 ple of the diurnal rhythm of which I have spoken, the pliable 

 yet more or less set mold within which the day's activities 

 take place. These regidar diurnal movements of birds I 

 have termed migrative because they were concerned with 

 colonies, or flocks, or at least included large numbers of birds 

 rather than pairs of individuals. They were instigated by 

 two impelling motives, the search for food for the young 



