Variations in Movement and Habitat Selection by Eurasian Curlew at Two Important Sites in Europe Throughout Winter

Shorebirds aim to replenish their body reserves during the wintering season to ensure their subsequent survival and to improve their breeding performance. However, their space use depends on their fluctuating resource availability and energy requirements throughout the winter. Hence, this study aimed to determine if the space and habitats used by Eurasian curlews (Numenius arquata) were influenced by their wintering site and stage. Sixty-two curlews were equipped with GPS tags at two major wintering sites in Europe with contrasting waterbird density: the Pertuis Charentais (PC) in France and the German part of the Wadden Sea (WS). Their home ranges (HRs) and foraging habitat selection were compared according to three wintering stages requiring different energy demands (i.e., early winter, mid-winter and late winter before migration). Curlews exhibited similar HR sizes at both sites throughout the winter, suggesting no effect of waterbird density on individuals' space use. HR sizes were larger during the day than at night and showed high inter-individual variability, unrelated to sex. Notably, the HRs were larger during the first winter stage (i.e., Arrival-September), with curlews spending a greater proportion of time on mudflats, and selecting distinct foraging areas located further from the coast at this stage. Curlews in the WS fed mainly on the mudflats, while curlews in the PC fed on the mudflats, but also on biogenic reefs, oyster parks and seagrass beds, the latter being favoured during the first stage. These results suggest the need for greater consideration of the distribution of curlews and other shorebirds at the beginning of the wintering season to define areas and habitats of importance to support future management and conservation measures. Indeed, birds are particularly prone to disturbance during the first winter stage, when tourism pressure on the coast is high and birds tend to be more mobile.