WEST 



Variable Seedeater, Yellow-bellied Seedeater (Sporophila nigricol- 

 lis), Blue-black Grassquit, ( Volatinia jacarina) , and Green-backed 

 Sparrow ( Arremonops conirostris ) , need vary their energy intake 

 for existence only slightly, with minor changes in temperature and 

 photoperiod throughout the year (Cox, 1960). 



Migrant species, however, must adjust to the climatic conditions 

 of two localities. Arctic and temperate breeding birds attain more 

 nearly uniform environmental temperatures by migrating to southern 

 latitudes in the winter. Therefore, the lack of metabolic acclimat- 

 ization in the Tree Sparrow (see above) maybe a result of spending 

 the whole year in a relatively constant climate. 



In contrast to permanent resident species, migrant birds must 

 increase their energy intake for migratory flights in the spring and 

 fall (Famer, 1955; Rautenberg, 1957; Kendeigh et al., 1960). The 

 added energy intake is used for the deposition of migratory fat, and 

 in caged birds, for motor activity at night (Zugunruhe). When fat 

 stores are completed and weather conditions are satisfactory, actual 

 flight, utilizing the stored fat, occurs. The pattern of added energy 

 intake for fat deposition alternated with migratory flights is repeated 

 until the final destination is reached (Wolfson, 1954). The added cost 

 of fat deposition and spring nocturnal unrest increases the daily 

 energy intake of White-crowned Sparrows by 30% to 50% (King and 

 Farner, 1956) and the intake of Tree Sparrows by 21% to 22% (West, 

 1960; Kendeigh et al., I960). 



Following migration, reproductive activities are initiated. The 

 amount of energy required to produce a clutch of eggs is undoubtedly 

 considerable although it has not been experimentally determined for 

 wild birds (Kendeigh, 1941). The added cost of incubation of eggs by 

 the female Tree Sparrow has been calculated to add about 22% to its 

 existence energy requirementperday (West, 1960). Kendeigh (196 lb) 

 shows that incubating House Wrens ( Troglodytes aedo n) also require 

 23% more energy while incubating. 



Most small passerines have a complete post nuptial molt in 

 the fall. The growth of new feathers requires energy. Metabolic 

 rates of the Chaffinch ( Fringilla coelebs) (Koch and deBont, 1944) 



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