GUGLIELMO, C.G.; CERASALE, D.J.; ELDERMIRE, C.; Univ. of Montana; Univ. of Montana; Univ. of Montana: A field test of plasma lipid metabolites as measures of stopover habitat quality for migratory birds

The refueling rate achievable at a particular site is thought to be a key determinant of its quality as a stopover for migrating birds. Methods that can be used to measure the rate of refueling will improve habitat assessment efforts, and also facilitate study of other factors that may influence stopover use, such as predation risk. Captive studies demonstrate that rate of mass gain in birds can be predicted from plasma lipid metabolite concentrations (Tiacylglycerol, glycerol, and B-OH-butyrate). This technique could provide a one-capture, individual-based measure of instantaneous refueling performance that could substantially reduce capture effort needed to measure refueling with conventional capture studies. In fact, field studies confirm significant differences in metabolite levels between sites that strongly suggest differences in refueling rate. This is the first study that attempts to validate the use of plasma lipid metabolites in the field by measuring refueling rate at different sites independently with mist-net capture data. Extensive, multi-year studies at Long Point Bird Observatory, Ontario, Canada indicate that refueling rates in spring differ markedly between the tip of Long Point and a banding station near the Lake Erie shore (Old Cut). We blood sampled a total of three hundred individuals of six passerine bird species during migratory stopover at the Tip and Old Cut stations in April and May 2002. Within each species, plasma metabolite levels will be compared between sites, and to mass gain rates estimated from the relationship between absolute body mass and time of day.