Differences in dietary specialization, habitat use and susceptibility to human disturbance influence feeding rates and resource partitioning between two migratory Numenius curlew species

Migratory shorebirds select stopover sites to fuel their migration across heterogeneous coastal landscapes with abundant prey resources. Quantifying the degree of dietary specialization between closely-related species and how they partition resources across different coastal habitat types during both spring and autumn migration could identify some interesting possibilities for conservation management given the extent of anthropogenic habitat degradation at critical stopover sites. Here we used a comparative approach to examine diet specialization and feeding rates of two migratory Numenius curlew species, Far Eastern Curlew Numenius madagascariensis and Eurasian Curlew N. arquata populations, at an important stopover site in the Yellow Sea, China, and to assess the influence of habitat type, presence of human disturbance (activities related to aquaculture and oil production), and migratory season on their feeding behavior. Far Eastern Curlews were more dependent on tidal crabs and exhibited less dietary flexibility than its closely-related congener. Feeding rates on crabs by Far Eastern Curlews were not significantly different between mudflat and Suaeda salsa saltmarsh habitat but were negatively influenced by human disturbance and were higher during spring migration. In contrast, these effects were not apparent for Eurasian Curlew which fed predominantly on ragworms in saltmarsh habitat. The differences in prey type and feeding rates between adjacent habitats and migration seasons could explain how these two congeners fit syntopically along coastal wetland resource gradients. The extensive utilization of S. salsa habitat by both species suggests that saltmarshes represent an important feeding habitat for these species and that further conservation efforts aimed at reducing human disturbance would benefit both species and may lead to improved feeding rates for Far Eastern Curlews.