Seasonal acclimatization to extreme climatic conditions by black-capped chickadees (Poecile atricapilla) in interior Alaska (64 degrees N).

Winters in interior Alaska (64 degrees N) are characterized by short photoperiod (5L : 19D) and chronic subfreezing temperatures. To determine if seasonal acclimatization of black-capped chickadees (Poecile atricapilla) at high latitude differs from that of conspecifics at lower latitudes, standard metabolic rates (SMR), metabolic response to low temperature (-30 degrees C), nocturnal hypothermia, body mass, fat reserves, and conductance were measured over two winters and one summer in three groups of seasonally acclimatized birds. Body mass and conductance did not vary with season, although furcular fat levels were higher in winter. Birds used nocturnal hypothermia when exposed to -30 degrees C in summer or winter. Although SMR did not vary seasonally, winter SMRs differed between the two winters of the study. Nocturnal hypothermia in summer and decreased SMR in response to extreme conditions may either reflect plasticity inherent to all populations of black-capped chickadees or may result from individual variation within this northern population.