Nycthemeral Movements of Wintering Shorebirds Reveal Important Differences in Habitat Uses of Feeding Areas and Roosts

Abstract

Most shorebirds depend on coastal habitats for much of their life cycle. The quality and diversity of feeding areas during the wintering period directly condition their winter survival, subsequent migration, and breeding success. During their wintering in France, shorebirds use intertidal areas for feeding, both in daylight and at night, depending on the availability of mudflats during the tidal cycle. In this context, we studied whether the bar-tailed godwit (Limosa lapponica) shows contrasting foraging behaviors and distributions between day and night in response to differences in visual capacities, prey availability, potential predation risk, and human activities. We carried out a fine-scale GPS tracking of birds at one of their main wintering sites along the French Atlantic coast. We predicted smaller foraging home ranges at night because of limits for godwits to detect prey visually, suggesting more sediment probing and less movement. Godwits used the entire time window when they have access to intertidal areas, but they faithfully selected distinct diurnal and nocturnal feeding areas using a low number of patches. This variability in space use highlights differences in selection of habitats, such as seagrass beds selected by most of the tracked godwits by day and used much less at night. In addition, distinct feeding distributions of monitored birds revealed interindividual variability in habitat selection, even more by night, most likely to reduce intraspecific competition. We therefore urge greater consideration of the night distribution of birds, rarely evaluated in shorebird studies, to define areas and habitats of importance to future management and conservation measures.