Determining breeding origins of semipalmated sandpipers staging in New Brunswick, Canada

Abstract

The Northumberland Strait and the Bay of Fundy are crucial refuelling sites for shorebird species migrating through Atlantic Canada. Many of these species are declining, including the Semipalmated Sandpiper (Calidris pusilla), a Nearctic breeding migratory shorebird that refuels in Atlantic Canada during southbound migration. The origin of Semipalmated Sandpiper’s population declines is not fully understood as these declines have not been identified as widespread or isolated to a specific Arctic breeding region. Currently, bill lengths are used as a proxy for breeding origin as Semipalmated Sandpiper bill length increases from west to east across the Arctic. However, bill length relationships confound with sex as females have longer bills than males. Therefore, deuterium (δ2H) signatures were used to track the breeding origin of juvenile Semipalmated Sandpipers. To elucidate the migratory connectivity of Semipalmated Sandpipers refueling in the Northumberland Strait and the Bay of Fundy we examined (1) the relationship between deuterium signature and bill length, (2) the origin of Semipalmated Sandpipers, (3) the relationship between breeding origin and timing of migration, (4) differences in breeding origin between years and refueling sites, and (5) the relationship between breeding origin and the amount of time spent refueling. We captured juvenile shorebirds on Maritime staging locations. We obtained blood samples for molecular sexing as well as feather samples for stable isotope analysis. We found that, though the relationships between migration timing and breeding origin varied among years, the proportional origins of birds did not change. Most birds are arriving from the eastern and central regions of the Arctic. Birds associated with an unusually early arrival in 2019 were from more southeastern breeding populations. Conversely, early arriving birds in 2018 came from more western and northern sites. Semipalmated Sandpiper arriving from more eastern and southern breeding populations had longer stopover durations in 2019. Climate on Arctic breeding grounds correlated with migratory timing. Colder temperatures and slightly later snowmelt in 2018 related to an earlier migration from northern and western breeding birds. Additionally, cooler temperatures, more precipitation, and earlier snowmelt in most southern and eastern breeding populations suggested more success and earlier migration for these populations in 2019. A large implication of this study is that stable isotope analysis of feathers will allow us to identify approximate breeding origin of birds staging in Maritime Canada. We look forward to assessing long-term trends and proportional breeding origin changes as additional years of data are obtained.