LIKNES, E.T.; GUGLIELMO, C.G.; SWANSON, D.L.*; Augustana College; University of Western Ontario; University of South Dakota: Fuel Storage And Mobilization Strategies Associated With Seasonal Acclimatization Of Resident Passerines

Seasonal acclimatization in small birds wintering in cold climates generally results in the upregulation of metabolism in winter to meet enhanced thermoregulatory demands. We measured lipid and glycogen stores, muscle fatty acid binding protein (H-FABP) levels, and circulating levels of triglycerides, free-fatty acids, glucose, and uric acid to determine whether, as part of the process of seasonal acclimatization, black-capped chickadees (Poecile atricapillus), house sparrows (Passer domesticus), and white-breasted nuthatches (Sitta carolinensis) modulate attributes of fuel storage, mobilization and/or transport to meet enhanced winter thermoregulatory demands. Carcass lipid mass varied little seasonally in chickadees, but was greater winter than in summer for sparrows (38%) and nuthatches (43%), however this variation was not significant. Pectoralis intramuscular lipid was from 22-56% greater in winter birds, but this difference was not significant. In most cases, muscle glycogen levels did not vary significantly between seasons or treatments. Pectoralis H-FABP was significantly elevated in winter in chickadees and nearly significantly in nuthatches. Seasonal patterns of plasma metabolite response to different temperature exposures showed little seasonal variation. Thus, fuel storage and mobilization do not appear to be major targets of adjustment associated with seasonal acclimatization in these species, but modulation of intracellular lipid transport may be an important component of seasonal acclimatization.