Seasonal abundance of shorebirds at the Guerrero Negro wetland complex, Baja California, Mexico

We studied the seasonal abundance of shorebirds at the Guerrero Negro wetland complex, Baja California Sur, Mexico, by carrying out twelve monthly censuses between July 2006 and June 2007. Total abundance ranged from 18,000 birds in June to 370,000 in December. Shorebirds were most abundant in the Ojo de Liebre Lagoon (peak count: 250,000 birds), followed by the Guerrero Negro Lagoon (95,000) and the man-made wetlands created by the Guerrero Negro saltworks (83,000). The most abundant species were Western Sandpiper Calidris mauri (41% of all observations), Marbled Godwit Limosa fedoa (27%) and Short-billed Dowitcher Limnodromus griseus caurinus (11%). The lagoon complex supports >1% of the flyway population of ten shorebird species and is particularly important for Marbled Godwit (about half the world population), Red Knot Calidris canutus (32–64% of the roselaari subspecies population) and Short-billed Dowitcher (69% of the caurinus subspecies population). The area is also an important wintering site for Long-billed Curlew Numenius americanus, Snowy Plover Charadrius alexandrinus and Dunlin Calidris alpina. All of these populations are identified in the U.S. Shorebird Conservation Plan (2001) as of conservation concern. We identified five patterns of seasonal abundance. Almost all species were most abundant in winter, were absent or only occurred in low numbers in summer and varied in spring and autumn. Red-necked Phalarope Phalaropus lobatus, which only occurred in substantial numbers in autumn, stood out as an exception.