Social status does not affect resting metabolic rate in wintering dark-eyed junco (Junco hyemalis)

Studies of wintering birds have demonstrated a correlation between social r ank and energy expenditures. It is assumed that dominance is energetically costly because of increased activity, possibly caused by elevated androgen levels. As winter acclimatization leads to an increase in metabolic rate, m aintaining dominance status in a cold climate can be a substantial challeng e. We measured resting metabolic rates in dominant and subordinate dark-eye d juncos (Junco hyemalis) Living in small groups in a controlled winter env ironment. We found no significant effect of social rank when controlling fo r body size. It has been shown previously that high testosterone levels dur ing the nonbreeding season can lead to higher body conductance, fat loss, a nd higher nocturnal body temperature. A hypothesis explaining our result is that for juncos it is preferable to maintain low androgen levels during wi nter and to maintain social rank using a mechanism other than higher agonis tic activity.