Overwintering passerines in boreal regions require high metabolic rates in order to maintain a normal body temperature in the more extreme environmental conditions of the north i.e. shorter day length that reduces foraging time (Cooper and Gessman 2005). Small passerine, in particular the Black-Capped Chickadee (Parus atricapillus) henceforth chickadee, which weigh in at around 11g and have a high surface-area to volume ratio lose heat very quickly and must have a higher than normal rate of metabolic heat production to overcome this small size (Grossman and West 1977). However, chickadees have adaptations to survive extreme cold: overnight they reduce their body temperature (Tb) in response to the winter ambient temperature (Ta) resulting in
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This is further proven in difference between energy stored in fat and energy expended overnight which is positive in November, suggesting that they’ve started storing more fat than they’re expending (Table 1) (Chaplin 1974). This value increases through February and is probably related to how chickadees use shivering to regulate body temperature. It can also be shown that around midwinter the percent of body composed of fat increases significantly in the afternoon compared to the morning, this is in order to gain enough energy to sustain themselves overnight (Table 1) (Chaplin 1974). This aside, both Chaplin (1976) and Gessman and Cooper (2005) found that mass and depth of hypothermia were unrelated suggesting that poor energy reserves do not cause hypothermia. Similarly, Cooper and Swanson (1994) concluded that insulation is not a primary component of winter acclimatization in chickadees because the lower critical temperature (temperature at which heat loss overcomes heat production) was not significantly different in summer and winter birds. Furthermore, an interesting conclusion is made by Chaplin (1976) suggesting that “[H]ypothermia is not a last resort but a first defense.” Thus, chickadees increase energy intake and expenditure in order to help thermoregulate during cold
This is further proven in difference between energy stored in fat and energy expended overnight which is positive in November, suggesting that they’ve started storing more fat than they’re expending (Table 1) (Chaplin 1974). This value increases through February and is probably related to how chickadees use shivering to regulate body temperature. It can also be shown that around midwinter the percent of body composed of fat increases significantly in the afternoon compared to the morning, this is in order to gain enough energy to sustain themselves overnight (Table 1) (Chaplin 1974). This aside, both Chaplin (1976) and Gessman and Cooper (2005) found that mass and depth of hypothermia were unrelated suggesting that poor energy reserves do not cause hypothermia. Similarly, Cooper and Swanson (1994) concluded that insulation is not a primary component of winter acclimatization in chickadees because the lower critical temperature (temperature at which heat loss overcomes heat production) was not significantly different in summer and winter birds. Furthermore, an interesting conclusion is made by Chaplin (1976) suggesting that “[H]ypothermia is not a last resort but a first defense.” Thus, chickadees increase energy intake and expenditure in order to help thermoregulate during cold