BIRD ADAPTATIONS 

 SUMMARY 



Birds maintain relatively constant body temperatures by reg- 

 ulating mechanisms for heat production and heat loss over a wide 

 range of environmental temperatures. 



The variable insulative ability of the plumage is the chief 

 mechanism for prevention of heat loss. As temperature falls, in- 

 sulation gradually increases until it reaches a maximum. At the 

 same time, peripheral circulation decreases and heat is retained 

 in the core of the body. Simultaneous with the increase in insulation, 

 shivering increases as the ambient temperature drops. After the 

 insulation reaches its maximum, metabolic mechanisms alone main- 

 tain homeothermy until the lower limit of temperature tolerance is 

 reached. In most small passerines, the total effect of combined in- 

 sulation and shivering responses to temperature results in a curvi- 

 linear relationship of metabolism to temperature, with no prolonged 

 thermoneutral zone indicated. 



Birds acclimated to low constant temperatures in the laboratory 

 generally have higher metabolic rates at any temperature than those 

 acclimated to warm temperatures. Birds acclimatized to different 

 seasons, however, show little change in metabolic response at ther- 

 moneutral temperatures. Seasonal changes in thermoregulatory 

 mechanisms involve an increased ability to produce heat by increas- 

 ing the metabolic rate in the cold of winter for extended periods of 

 time and possibly an increase in the amount of plumage insulation. 



Existence energy requirements of small wild birds living in 

 temperate regions are increased in the winter. Permanent residents 

 may have a more pronounced seasonal difference in their ability 

 to tolerate low temperatures than migrant species since they en- 

 counter greater extremes of temperature. 



The added daily cost of nocturnal unrest and of depositing mi- 

 gratory fat differs slightly among migrant birds according to the 

 length of time spent in premigratory preparation and in the average 



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