EXTRINSIC AND INTRINSIC SOURCES OF VARIATION IN PLASMA LIPID METABOLITES OF FREE-LIVING WESTERN SANDPIPERS (CALIDRIS MAURI)

Abstract

Abstract Plasma lipid metabolites may be useful indicators of mass changes in migratory birds. To test utility of plasma metabolites in field studies, we examined effects of several extrinsic (bleed time, time of day, location) and intrinsic (body mass, sex, age, migratory state) factors on plasma concentrations of triglycerides (TRIG), glycerol (GLYC), and B-OH-butyrate (BUTY) in free-living Western Sandpipers (Calidris mauri). TRIG and GLYC decreased rapidly following capture (2–20 min), whereas BUTY did not change. GLYC and BUTY were negatively correlated to body mass. TRIG was positively correlated to body mass in migrant females, but not consistently in migrant males, or in females captured on the wintering grounds. Taking into account other sources of variation, the two measures of lipid utilization (GLYC and BUTY) varied little through the year. TRIG showed the greatest potential for use in field studies. TRIG was lowest during winter, when birds were leanest, and highest during spring and fall mig...