Variation in resource use between adult and juvenile Semipalmated Sandpipers (Calidris pusilla) and use of physiological indicators for movement decisions highlights the importance of small staging sites during southbound migration in Atlantic Canada

Abstract

Semipalmated Sandpipers (Calidris pusilla) are Arctic-breeding shorebirds that use staging sites in Atlantic Canada during their annual migration to South America. The Bay of Fundy has long been recognized as a critical staging site for migrating Semipalmated Sandpipers and supports a large prey base. The diet of adult sandpipers in the Bay is flexible but the diet of juveniles, which arrive later, is not well documented. Comparatively little is known about the prey base and how it is utilized by sandpipers at sites in Atlantic Canada outside the Bay. Plasma metabolite measures can provide useful insight to assess habitat quality for sandpipers and have not yet been measured in Semipalmated Sandpipers in Atlantic Canada. To address these knowledge gaps we sampled shorebird habitat to estimate invertebrate availability in the Bay of Fundy and the Northumberland Strait. Concurrently, we collected blood samples from adult and juvenile sandpipers for analysis of plasma metabolite levels and isotopic estimates of dietary niche in both regions. We found that sites on the Northumberland Strait hosted a more diverse and variable prey base than sites within the Bay of Fundy, and that sandpipers were selective when foraging there, appearing to prefer bivalves. Juveniles may occupy a broader dietary niche than adults along the Northumberland Strait, though appear to gain weight as efficiently. Sandpipers sampled along the Northumberland Strait had higher plasma triglyceride concentrations than those within the Bay of Fundy, which may suggest differences in fattening rate or dietary fat intake. Sandpipers that had lower triglyceride concentrations on the Northumberland Strait were more likely to move into the Bay of Fundy, while sandpipers with high triglyceride values tended to remain on the Strait. These data suggest that sandpipers made movement decisions within the region depending on their physiological state. Our results suggest adult and juvenile Semipalmated Sandpipers successfully use a variety of staging habitats in Atlantic Canada. This is an encouraging finding for sandpiper conservation in the region, but also indicates that maintaining access to a broad variety of staging habitats is critical, supporting calls for stronger conservation measures throughout the region.

Shorebirds exhibit niche partitioning on multiple dimensions at a small staging site on the Northumberland Strait, New Brunswick, Canada

“…The results of this study add to the growing pool of research suggesting small coastal staging sites are important for the success of migratory shorebirds in Atlantic Canada (Doiron 2021;Linhart et al 2022Linhart et al , 2023, and calling for recognition of a combination of these small sites within the region (McKellar et al 2020). The Northumberland Strait is geographically close to the Bay of Fundy, a site of hemispheric importance to migratory shorebirds (WHSRN 2019), but these staging locations are structurally very different (Bellefontaine 2020;Linhart et al 2022). It is possible these structural and environmental differences allow the Northumberland Strait to host more diverse shorebird communities than the Bay of Fundy, where the shorebird population is dominated by Semipalmated Sandpipers (Hicklin 1987;Bellefontaine 2020).…”

“…However, it is crucial to recognize the role these sites play during shorebird migration (Fuller 2003;Van Brederode and Roersma 2020). The results of this study add to the growing pool of research suggesting small coastal staging sites are important for the success of migratory shorebirds in Atlantic Canada (Doiron 2021;Linhart et al 2022Linhart et al , 2023, and calling for recognition of a combination of these small sites within the region (McKellar et al 2020). The Northumberland Strait is geographically close to the Bay of Fundy, a site of hemispheric importance to migratory shorebirds (WHSRN 2019), but these staging locations are structurally very different (Bellefontaine 2020;Linhart et al 2022).…”

“…While we did not also collect samples from birds at CJ, we know from previous work in the region that shorebirds make frequent, short FACETS Downloaded from www.facetsjournal.com by 44.224.250.200 movements between these and other sites in the Northumberland Strait (Doiron 2021;Linhart et al 2023). This, coupled with the fact that the prey base does not differ significantly between PCAP and CJ (Linhart et al 2022), suggests that plasma isotopes of shorebirds captured at PCAP likely reflect diets across a range of local foraging habitats.…”

“…However, coastal sites outside the Bay also provide important habitat for a wide range of species (Atlantic Canada Shorebird Survey 2022). These smaller sites have received less attention, but recent and ongoing work suggest that they can support birds as they prepare for migration (Doiron 2021;Linhart et al 2022Linhart et al , 2023. Coastal staging sites on the Northumberland Strait in New Brunswick, Canada, host a diverse shorebird community that, in late summer, includes Semipalmated Sandpipers, White-rumped Sandpipers (Calidris fusicollis), Semipalmated Plovers (Charadrius semipalmatus), Greater and Lesser Yellowlegs (Tringa melanoleuca and Tringa flavipes), Least Sandpipers (Calidris minutilla), and Short-billed Dowitchers (Limnodromus griseus) (Atlantic Canada Shorebird Survey 2022).…”