The Effects of Exogenous ACTH on Aggression in Mountain Chickadees

Abstract

Aggression, especially male-male aggression, has been well documented in many taxa to be caused by an increase of the sex hormone, testosterone. However, in birds the link between testosterone and aggression is equivocal. Studies on this subject have produced contradictory results leading some to investigate other mechanisms that may be responsible for this increase in aggression. We examined aggressive behavior in Mountain Chickadess, Poecile gambeli, that were injected with either adrenocorticotropin hormone (ACTH), which causes an acute rise in corticosterone, or saline control solution. We found that ACTH birds were faster to return to the nest and would get closer to a speaker playing a male Mountain Chickadee song. However, we did not see any difference in number of songs sang between the groups. These results suggest that corticosterone levels and the HPA axis play a role in mounting an aggressive response to a perceived intruder.