Waterbird communities and wetland dynamics in the Mexican Highlands, 1951–2006

Many North American migratory waterbird species rely on wintering and stopover sites in the Northern Highlands of Mexico, several of which have experienced habitat loss or degradation over the last century. Despite this, the long-term patterns of waterbird abundance and the state of the wetlands themselves had not been analyzed. Changes in abundance and distribution of 3.4 million birds belonging to 19 waterbird taxa that winter in the Mexican Highlands were assessed using data from the United States Fish and Wildlife (USFWS) aerial surveys carried out between 1951 and 2006. Additionally, water occurrence at 29 wetlands used by these birds was inferred from satellite imagery corresponding to the bird count dates by calculating water surface area using Google Earth Engine. Bird abundance between 1975 and 2006 and environmental variables were modelled using Generalized Linear Mixed Models to identify determinants of wetland use by these groups of wintering waterbirds. Total sampled abundance in the Highlands was between 125,000 and 500,000 individuals of the different species of waterbird per year, and their abundance was highly variable between sites and years. The sites with the highest average abundance were Laguna de Babícora and the wetland complexes from Laguna Bustillos to Laguna de los Mexicanos in the northwestern section of the Highlands, as well as the wetlands in the sierra of the state of Durango, to the south-southeast of the former. Water permanence was different between the six subregions into which the wetlands were grouped, despite waterbody size not being significantly different between them. Overall, waterbirds were more abundant in semi-permanent sites, and abundance was explained best by water surface area plus total precipitation of the previous 12 months. Geese in the area exhibited site fidelity and this reflected in site-specific variables included in the best model. Abundance of diving ducks was explained best by water surface area, while that of dabbling ducks was so by water permanence plus water surface area. Our work supports that most birds preferred reliable, natural wetlands over human-modified ones even if the latter were larger, and this has clear implications for habitat management in this semiarid region.