Niche partitioning and behaviour of migratory shorebirds in the Northumberland Strait and Bay of Fundy

Abstract

Animal populations take advantage of environmental heterogeneity to partition themselves into microhabitat niches. Such partitioning plays an important role in determining interspecific competition and community structure by allowing multiple species to coexist. Many species of shorebirds use stopover sites in Atlantic Canada to fuel their annual southbound migration in late summer and early fall. The Bay of Fundy is recognized as a landscape of hemispheric importance for migratory shorebirds, and hosts hundreds of thousands of Semipalmated Sandpipers annually. Other stopover sites on the eastern coast of New Brunswick, Canada, host smaller but more diverse shorebird populations. There is a lack of research on stopover ecology of whole shorebird communities in New Brunswick, especially at small coastal stopover sites. We examined stopover ecology at staging areas in the Bay of Fundy and Northumberland Strait to examine niche dynamics relative to shorebird behaviour and habitat use. Foraging strategies and rates varied among shorebird species at stopover sites on the Northumberland Strait and also between Semipalmated Sandpipers in the Bay of Fundy and Northumberland Strait. We found that Short-billed Dowitchers primarily forage by probing, and Semipalmated Plovers forage by pecking. Semipalmated Sandpipers, White-rumped Sandpipers, Least Sandpipers, and Yellowlegs used a combination of pecking and probing. Diets also varied between species and sites. We found that Semipalmated Sandpipers and Semipalmated Plovers consume generalist diets, while the diets of Short-billed Dowitchers and White-rumped Sandpipers were more specialized for specific food sources. Different taxa face foraging constraints based on morphological features, which creates both spatial and behavioural segregation. This was evident on the Northumberland Strait, probably because greater environmental heterogeneity in small coastal sites created more dimensions for segregation than large mudflat sites. As a result, a wider diversity of species can co-exist. Small coastal sites constitute important stopover habitat for migratory shorebirds outside of the Bay of Fundy. These findings broaden our understanding of stopover ecology of multi-species flocks and indicate that conservation of small coastal sites is also important for success of migratory shorebirds in Atlantic Canada.