BIRD ADAPTATIONS 



Yellow Buntings and Ortolans (Wallgren, 1954) increased 10% to 

 26% during molting. The increases, however, are variable, and it 

 appears that the greatest energy cost occurs during growth of 

 the large flight feathers of the wing and tail (Koch and deBont, 

 1944). It is doubtful that' the gradual loss and replacement of fea- 

 thers causes a measureable lowering of body insulation in most 

 passerines, and any metabolic increase, therefore, is due to the pro- 

 duction of new feathers (King and Famer, 1961). 



Davis (1955) did not find an increase in metabolized energy of 

 House Sparrows during molting, although his data exhibited greater 

 variability at this time. King and Famer (1961) have pointed out that 

 the added daily cost of producing new feathers is so small that it 

 might not be detected infood consumption experiments. West (1960), 

 however, found a 27% increase in metabolized energy of molting 

 Tree Sparrows for over one week. This may have been during the 

 time of flight feather regeneration and an average value over several 

 weeks might be lower. 



When the values for fatdeposition, migration, reproduction, and 

 molting are added to the daily existence level, the total energy ex- 

 penditure of a single species canbe traced throughout the year (Fig. 

 13). The added cost of living a free existence as opposed to a caged 

 existence may be greater in the winter than in the summer due to 

 the difficulty of finding food. The uniform spacing of energy demand- 

 ing activities is such that the average daily intake of energy is 

 about the same throughout the year. 



A species must be confined to localities where it can secure 

 enough energy not only for existence, but also for all its essential 

 activities. Therefore, climate, and particularly temperature, plays 

 a major role in controlling distribution by excluding species from 

 regions which impose energy requirements exceeding metabolic 

 capabilities. 



313 



