Habitat use by migrating Whimbrels (Numenius phaeopus) as determined by bio-tracking at a stopover site in the Yellow Sea

Stopover sites are critical for refueling and resting by migrating birds. Clarifying the habitat requirements of migratory birds during stopover is important for understanding migration ecology and for conservation management. Habitat use by migratory birds at stopover sites, however, has been inadequately studied, and individual variation in habitat use among species is largely unexplored. We tracked the movement of migrating Whimbrels, Numenius phaeopus, using Global Positioning System–Global System for Mobile Communication tags at Chongming Dongtan, an important stopover site in the South Yellow Sea, China, in spring 2016 and in spring and autumn 2017. Multinomial logistic regression and multimodel inference were used to detect the effects of the individual bird, the diel factor (day vs. night), and tide height on the habitat use by Whimbrels during the stopover. The activity intensity of Whimbrels was lower during the night than during the day, while the maximum distance that tagged Whimbrels moved was similar between day and night. The saltmarsh and mudflat were intensively used by all of the individuals in all three seasons: > 50% and 20% of all records were obtained from the saltmarsh and mudflat, respectively. Habitat use significantly differed among individuals; the farmland and woodland were used by some individuals in spring 2016, while the restoration wetland near the intertidal area was used by some individuals in 2017. In general, the saltmarsh, farmland, and woodland were more frequently used in the daytime, while the mudflat was more frequently used at night. As tide height increased, the use of the mudflat decreased while the use of the saltmarsh increased. The results suggest that individual-based bio-tracking can provide detailed data on habitat use both during the day and at night. Differences in habitat use among individuals and periods highlight the importance of diverse habitats for bird conservation.