First-ever data on space use by breeding Whiskered Terns Chlidonias hybrida using bio-logging

Summary Wetlands are critical ecosystems for many species of conservation concern, including migratory birds. These species face resource depletion and unpredictability in the context of global change and are expected to adjust their space use accordingly. Understanding how waterbirds use space and identifying their foraging needs are essential for guiding conservation efforts. Here, we present preliminary results on the fine-scale space use of a wetland flagship species, the Whiskered Tern Chlidonias hybrida , in La Brenne, a historical French breeding stronghold. The species is listed as ‘Vulnerable’ in France and breeds in only a few large wetlands. For the first time, we equipped four adult terns with miniature GPS tracking devices, providing unique, high-resolution data on their daily movements throughout the breeding season (i.e. pre-incubation, incubation, rearing, and post-breeding). Our results showed that most daily foraging trips did not exceed 2–3 km, resulting in relatively small home ranges (ranging from 2.00 km 2 to 14.95 km 2 ). Values were higher during the post-breeding period (up to 8 km from the nest and home range size up to 74.45 km 2 ). Furthermore, we found that Whiskered Terns remained faithful to their foraging areas throughout the season and preferentially foraged in ponds – especially those near their colony – compared with other potential foraging habitats. On average, 91% of foraging positions occurred in ponds and 9% in grasslands. We also provide practical details on bird capture and device attachment methods. Finally, this pioneering bio-logging study offers promising prospects for future research on the movement ecology of Whiskered Terns, which could be invaluable for their conservation.