Two decades of change in nonbreeding population sizes of shorebirds and other waterbirds in the Iwik area of Parc National du Banc d’Arguin, Mauritania

Migratory waterbirds depend on networks of wetlands during their seasonal migrations between breeding grounds and nonbreeding areas. The Parc National du Banc d’Arguin, Mauritania, is one such site that migratory waterbirds of the East Atlantic Flyway heavily rely on as a nonbreeding area. Based on yearly systematic counts that started in 2003 at the Iwik peninsula of Banc d’Arguin, we evaluated temporal changes in the numbers of waterbirds, including shorebirds, wading birds, pelicans, cormorants, gulls and terns, over a period of 21 years. Overall, after a decade (2003-2012) of strong declines in both the total numbers of all waterbirds and shorebirds, numbers of both groups became more stable (2013–2023). Local breeding populations of large-bodied fish-eating waterbirds increased during most of the study period but showed sudden declines over the last two years, possibly related to exposure to Avian Influenza. Numbers of gulls and terns were generally stable. Among the shorebirds, numbers of the plover species were stable, Red Knot numbers became stable after a decade of decline, but Bar-tailed Godwits showed a continued decline. Whimbrel was the only shorebird species that showed a steady and significant local increase. This study indicates that small-scale, regular counting of waterbirds is a useful addition to synoptic flyway-scale count efforts in monitoring long-term population trends.