Differences in use of Northumberland Strait habitat and fattening rates among migratory shorebird species

Abstract

Migratory shorebirds rely on stopover sites to rebuild fat stores during migration. The habitat used within each stopover site, and the strategies used to build fat, can vary between species and stopover. In the Canadian Maritimes, the Bay of Fundy has been the focus of migratory shorebird research given the large population of shorebirds it supports. Though less used, other sites on the New Brunswick and Nova Scotia coast, including the Northumberland Strait, also host a diverse shorebird assemblage. A variety of shorebird species use the mudflats, sandflats, and saltmarshes along the Northumberland Strait coast during their fall migration. It is unknown whether species in this region are using the available habitat on a mudflat-by-mudflat basis in this region, and how much fat they are building. We predicted that due to the different pressures associated with long- and short-distance migrations, short-distance migrant species will adhere to a slowly fattening, short stay, many movement strategy, while long-distance migrant species will build fat quickly over a longer period of time with few movements. We investigated duration of stay, habitat use and plasma metabolites of Least Sandpipers (Calidris minutilla Vieillot), Semipalmated Sandpipers (Calidris pusilla L.), White-rumped Sandpipers (Calidris fuscicollis Vieillot), and Semipalmated Plovers (Charadrius semipalmatus Bonaparte) to characterize their use of the Northumberland Strait, and to compare said use between species. Usage of habitat and length of stay were determined through radio telemetry, and plasma metabolites were investigated by measuring plasma triglyceride and B-hydroxybutyrate concentrations. Least Sandpipers had the lowest plasma triglyceride and highest B-hydroxybutyrate concentrations suggesting that they were fattening the slowest. Semipalmated Sandpipers and Semipalmated Plovers both had high triglyceride and low B-hydroxybutyrate, while White-rumped Sandpipers occupied an intermediate position with low triglyceride and B-hydroxybutyrate. All sandpiper species in this study had similar mean minimum stopover durations, between 14-19 days, while the plovers stay for up to a week longer. The species also exhibited differences in the habitat they used. Semipalmated Sandpipers ranged more widely than did the other species, though there was a universal preference for habitat nearest to our catching site. These findings provide evidence that shorebirds using the Northumberland Strait are not adhering to the predictions associated with expected stopover behaviour in short- and long-distance migrants. Instead, each species is using unique and variable strategies to build fat stores during their stopover. We also highlight the need for continued research of multiple species stopover strategies and the use of the Northumberland Strait as migratory shorebird habitat as limited movements between sites suggest region wide protection may be needed to conserve shorebirds.