O’REILLY, K.M.*; FORTIN, J.K.; GJELTEN, A.A.; Univ. of Portland, OR; Washington State Univ., Pullman; Univ. of Portland, OR: Elevated adrenocortical response to stress in overwintering chickadees and nuthatches at high elevation

Birds living at high elevations experience more rigorous winter weather conditions than birds living at low elevations. One mechanism birds may use to cope with cold temperatures and increased metabolic needs is elevation of plasma corticosterone levels, both baseline and stress-induced levels. We examined three species of passerines living at 1500m in the eastern Cascade range above Bend, Oregon. Mountain chickadees ( Poecile gambeli ) and red-breasted nuthatches ( Sitta canadensis ) sampled in mid-February had higher stress-induced levels of corticosterone (22-25 ng/ml, obtained 30 min after capture) than individuals sampled at the beginning and end of March (approx. 15 ng/ml). Baseline levels collected within 4 min of capture did not differ for either species between the three sampling periods (range 1-3 ng/ml). Dark-eyed juncos ( Junco hyemalis ) did not arrive at the site until late February. In samples obtained at the beginning and end of March, maximum (7-15 ng/ml) and baseline (1 ng/ml) levels of corticosterone did not differ between dates. In all three species, every individual had a robust adrenocortical response to stress. The elevated stress-induced levels of corticosterone observed in chickadees and nuthatches during the mid-February sampling period corresponds to the coldest temperatures observed (-5C), possibly indicative of a coping mechanism for cold temperatures.