Threatened Birds in a Changing Mediterranean Wetland: Long-Term Trends and Climate-Driven Threats

Understanding the impact of climate change on waterbirds, particularly those of conservation concern, is essential for their long-term management and effective conservation. In arid regions such as North Africa, wetlands of international importance have been affected by severe drought events, but their impact on waterbirds is still not well understood. Here, we assess the population dynamics of four emblematic resident species (<i>Aythya nyroca</i>, <i>Marmaronetta angustirostris</i>, <i>Oxyura leucocephala</i>, and <i>Porphyrio porphyrio porphyrio</i>) in a North African Ramsar site (Garaet Hadj Tahar marsh, Northeast Algeria), and determine the climatic variables (temperature, precipitation, and drought index) that best predict the change in abundance in wintering and breeding seasons. We used a long-term survey of regular counts during the wintering and breeding seasons of 2002-2019. The temporal trend of waterbird abundance differed between species and seasons. Species showed different sensitivities to different climatic variables at different time windows preceding the wintering and breeding seasons. We found that the population dynamics of the endangered <i>O. leucocephala</i> in the wintering and breeding seasons were best predicted with the drought index, whereas those of <i>P. p. porphyrio</i> were best correlated with maximum temperature. Population dynamics during the wintering and breeding season of the two other species were best explained with either maximum temperature, precipitation, average temperature, or drought. Species responded differently to warming and drought. The most endangered species (<i>O. leucocephala</i>) showed population declines in drier years, whereas less threatened species (<i>A. nyroca</i>, <i>M. angustirostris</i>, and <i>P. p. porphyrio</i>) exhibited either positive or negative correlations. The observed temporal increase in vegetation cover was positively correlated with the wintering population size of <i>O. leucocephala</i>, as well as the breeding population size of <i>P. p. porphyrio</i> and <i>M. angustirostris</i>. These findings highlight the urgent need for climate-adaptive conservation strategies to sustain wetland biodiversity and ecosystem resilience in the face of increasing climate stressors, aligning with the global sustainability goals for biodiversity conservation and ecosystem management. Our results suggest that future increases in temperatures and drought severity might threaten endangered waterbirds and benefit more common species in the region.