Half a century of changes in waterbird populations in a semiarid wetland system

Mexican inland wetlands in the arid and semiarid interior highlands historically held very large numbers of waterbirds. However, they have been deteriorated by agriculture, industrial and urban development, tourism and aquaculture, although the effects of this are known poorly. At the southern end of the Central Plateau of Mexico, the region of El Llano, in the states of Aguascalientes and Jalisco, is densely dotted with wetlands amidst an agricultural landscape. The wetlands that existed at the time of Spanish contact have disappeared or been modified, but many new ones have been created, including large and mid-size reservoirs, as well as small cattle watering tanks. The importance of this region for waterbirds was analyzed based on the data from the USFWS mid-winter Mexican waterfowl surveys, and surveys by ourselves in 1984–1985 and from 2010 to 2014. The data exhibited a peak in diving ducks in the late 1970s, which might reflect reservoir restoration and, or creation. Wetland water levels as well as their use by waterbirds was highly variable during the study period, and some sites that were important in 1984–1985 have silted and dried up. The major waterbird trend in the survey area has been a steady increase in the number of the threatened Mexican Duck since the late 1970s until 2010–2011, that might have been resulted from a reduction in its hunting and egg collecting, and, or improvement in nesting habitat, along with reservoir creation or restoration.