Assemblage of Shorebirds and Seabirds on Rocha Lagoon Sandbar, Uruguay

Rocha lagoon is known to present many migrant and resident seabird and shorebird species. In order to improve the knowledge of the birds community that inhabit this area, changes in richness and abundance of the shorebird and seabird assemblage (Charadriidae, Scolopacidae and Laridae) were studied during a year (period 2000-2001), and some of the habitat characteristics selected by the species were described. Data on richness and abundance of birds were obtained through seasonal censuses in an area of 60 ha in the lagoon's sandbar. Twenty four species of seabirds and shorebirds were registered in the study area corresponding to summer migrants, winter migrants, and residents. Richness was low in July (9) and November (11) when the highest peaks of abundances of Common Terns (Sterna hirundo) and South American Terns (S. hirundinacea), respectively, were registered. Shorebirds were in general, less abundant but showed high species richness, with the White-rumped Sandpiper (Calidris fuscicollis), the Rufous-chested Dotterel (Charadrius modestus), and the American Golden Plover (Pluvialis dominica) being the three most common species. Nesting of the Yellow-billed Tern (S. superciliaris) was registered in the study area during two consecutive reproductive seasons between October and February. Remarkable seasonal variation was observed, principally related with the arrival of migratory species in winter (July) and the end of spring (November). Rocha lagoon's sandbar offers a variety of habitats used for resting, feeding and breeding by migratory and resident species. Particular characteristics of the study area are also possibly related to the high richness and the temporal variation observed.