SWANSON, DL*; THOMAS, NE; University of South Dakota: Relationship of plasma triglycerides and creatine kinase to overnight temperature in winter acclimatized small birds

Plasma triglyceride (TG) levels and creatine kinase (CK) activity may increase during long-distance flights in migratory birds, TG as an additional lipid fuel source and CK as a result of flight-induced muscle damage. Plasma profiles of TG and CK have not previously been reported for small birds wintering in cold climates, but prolonged intense shivering during cold temperatures could necessitate additional lipid fuel supply and result in muscle damage. We measured early morning levels of plasma TG and CK activity in four species of small birds overwintering in South Dakota, American tree sparrows (Spizella arborea), dark-eyed juncos (Junco hyemalis), house sparrows (Passer domesticus) and American goldfinches (Carduelis tristis). We hypothesized that TG levels and CK activity might vary as a function of overnight temperature, with higher levels during colder temperatures that require increased shivering thermogenesis. TG levels were negatively related to overnight temperature in all species, but significantly so only for dark-eyed juncos (R² = 0.16, P = 0.027). Plasma CK activity was also negatively related to overnight temperature in all species, but was only significantly related to temperature in American tree sparrows (R² = 0.37, P = 0.035). These results suggest that TG might contribute to lipid supply to shivering muscles during intense shivering in juncos, but this route does not appear to be universal among small birds during high levels of shivering thermogenesis. Similarly, intense shivering may incur some muscle damage in some species, but such muscle damage is apparently not universal among small birds. Plasma CK activity was also significantly lower in house sparrows than in other species, suggesting that muscle damage with intense shivering may vary with body size.