Rapid expansion of croplands in Chihuahua, Mexico threatens declining North American grassland bird species

Grasslands are one of the most imperiled ecosystems worldwide. Conversion to cropland and desertification, including shrub encroachment, are primary factors behind the loss of temperate grasslands across the globe. Governments and conservation organizations in North America have identified the highest priority grasslands from Canada to Mexico in an effort to conserve grassland biodiversity, particularly migratory birds. Twenty-nine of 33 (88%) grassland-obligate bird species breeding in western North America's Great Plains are migratory and 90% of these overwinter in the Chihuahuan Desert. The 2.7 M ha Valles Centrales is a region of northern Mexico comprised of desert shrublands, mountains and grassland valleys. It supports wintering populations of 28 migratory grassland bird species from the Great Plains, in addition to threatened and endangered species in Mexico such as Aplomado Falcon (Falco femoralis), Pronghorn (Antilocapra americana mexicana) and others. Using remote sensing, we documented a 6.04% annual rate of cropland expansion in the Valles Centrales from 2006 to 2011, resulting in a loss of 69,240 ha of valley-bottom grasslands and shrub lands. Open grasslands are the principle habitat for most declining, grassland-obligate bird species. Expansion of center-pivot irrigated cropland was the primary driver of grassland loss. The area cleared for agriculture, as determined via remote sensing, exceeded the amount of land that had been permitted for land-use change to cropland, according to government records, by >2000%. As a consequence of this habitat loss, we estimate the winter carrying capacity for 28 species of grassland birds in this region has been reduced by approximately 355,142 individual birds. At the current rate, the ongoing expansion of ground-water irrigated cropland could eliminate the remaining low-slope valley bottom grasslands from the Valles Centrales region by 2025. Cumulative grassland losses in the Chihuahuan Desert could have severe impacts on global populations of declining migratory grassland birds, as well as several threatened and endangered species. Our findings demand an urgent call to action by governments and responsible resource management agencies to work with the agricultural sectors to address land use change, sustainable agriculture and grassland ecosystem services in this globally-important region for grassland birds and biodiversity.