Relationships between plasma metabolites and mass gain in semipalmated sandpipers during migratory staging in the Northumberland Strait

Abstract

Semipalmated Sandpipers are long distance migrants that depend upon staging sites to build reserves during their fall migration to non-breeding sites. Eastern breeding Sandpipers use sites in Atlantic Canada, such as Petit-Cap, NB, to prepare for migration to South America. Rates of mass gain are an important metric used to predict migratory success and assess site quality, although this is difficult to obtain given that it requires the recapture of individual birds, which is not feasible at many staging sites. Plasma metabolites are a useful tool for indicating these metabolic changes in mass over time, but these relationships have not been examined in freeliving Semipalmated Sandpipers, despite their widespread use in the literature. At the study site, Petit-Cap, recaptures are possible, allowing us to test this relationship. We examined plasma metabolites (plasma triglycerides, glycerol, and bhydroxybutyrate) in relation to changes in mass in recaptured Semipalmated Sandpipers at Petit-Cap, NB. We failed to detect relationships between plasma triglycerides and b-hydroxybutyrate and mass changes in recaptured Semipalmated Sandpipers, suggesting that inferences of mass changes through plasma metabolites should not be integrated over long time intervals. We did find a significant positive relationship between glycerol and mass gain. As an extension of studying migratory refueling, we also assessed diets of the shorebirds while staging at this site. We found that bivalves were contributing largely to diets of both adult and juvenile Semipalmated Sandpipers, with no significant differences in diet breadth between the two age classes. While collecting data for this study, we encountered a storm midway through the staging season. This provided an opportunity to examine the effects of short-term weather events upon body condition and refueling in staging Semipalmated Sandpipers. We found significant impacts upon migratory refueling in both recaptured and non-recaptured Semipalmated Sandpipers following a storm. Recaptured birds, on average, lost mass during the week following the storm. Similarly, non-recaptured birds had significantly lower size adjusted masses during versus before or after the week of the storm. These findings support previous research on the sensitivity of staging shorebirds to environmental fluctuations and highlight the importance of considering weather events a threat to migratory refueling. We emphasize the need for further investigation into the relationships between plasma metabolites, diet, handling, and weather upon rates of migratory refueling in Semipalmated Sandpipers.