Discovering the secret lives of White-headed Ducks: Unveiling population trends and phenology at Morocco’s two best wintering and nesting sites, Merja Fouwarate and Lake Sidi Boughaba

Due to its ongoing decline, the White-headed Duck (Oxyura leucocephala) is considered “endangered” and is, therefore, included in the IUCN Red List. It has been estimated that the species declined from 100,000 individuals in the early 20th century to only 8,000–13,000 individuals in the early 2000s. In order to investigate the trends and phenology of this species, we conducted fieldwork during the breeding and wintering seasons from 2011 to 2022 in Merja Fouwarate and at Lake Sidi Boughaba in Northwest Morocco. Our data show that the lowest numbers of individuals were observed in September, followed by a gradual increase throughout the autumn, reaching peak levels in the winter months between December and February. These peaks were observed in January at both locations in Merja Fouwarate, with 280 and 314 individuals recorded in 2021 and in 2022, respectively. At lake Sidi Boughaba, the peaks were lower, with 176 individuals recorded in 2021 and 120 individuals in 2022. In contrast, duck numbers declined throughout the spring, reaching their lowest point between March and May. In the course of the eleven-year observation period, the population of the species clearly increased. The population of Merja Fouwarate increased by 14.5 and 3.67 individuals on average each year, while that of Lake Sidi Boughaba increased gradually from 2011 to 2018 before declining in the years that followed.