Bill Length of Non-breeding Shorebirds Influences the Water Depth Preferences for Foraging in the West Coast of India.

Body size, bill length and shape determine foraging techniques, habitat selection and diet among shorebirds. In this study, water depth preferences of different shorebirds with different bill sizes in various habitats including mudflats, mangroves at Kadalundi-Vallikkunnu Community Reserve (KVCR) (19 shorebird species) and adjacent agroecosystems at Vazhakkad (12 species) were studied between 2017 and 2020. The bill length of the shorebirds was significantly and positively associated with the average water depth, where shorebirds were observed to forage. Shorebirds with shorter bill lengths preferred shallow waters and those with longer bills preferred deep waters for their foraging activities. Habitat type also had a significant effect on the shorebird occurrence. Eurasian Curlews in both mangroves and mudflats were observed in areas with a higher water depth compared to other species. This is due to the fact that shorebirds tend to specialise in feeding habitats or in prey items to reduce intraspecific competition and distribute themselves in space and time in accordance with the availability of their resources. The occurrence of some species in agroecosystems is attributed to the reduced food availability, habitat quality and other disturbances for shorebirds on tidal flats, which are critical for sustaining migratory phenology. The differences in bill morphology are crucial in determining diet, water depth, niche preferences and segregation. Morphological characters and hydrological rhythms determine specialisation in diet and habitat preference in shorebirds.