Although Baja California has not experienced loss of wetlands comparable in magnitude to that in California, some habitat changes have provoked changes in the abundance and distribution of wetland avifauna. This paper document ocurrence and changes in avian composition a long the wetland complexes in Baja California. Threats to the wetlands are primarily from resort and industrial developments being planned by international companies. Conservation of these vital avian habitats is a matter of concern to all ornithologist.

The Guerrero Negro-Ojo de Liebre and San Ignacio lagoons, located on the west coast of the Reserve, harbor at least twenty species of ducks and one species of brant from the Pacific Flyway. The average number of ducks annually recorded between 1977 y 1978 was 4,109 in Guerrero negro-Ojo de Liebre y 5289 en San Ignacio. The brant (Branta bernicla nigricans) is the only species that regulary winters in the lagoons since 1950. The lagoons harbor more than 50% of the entire species populations in wintertime. The average number of brants annualy recorded between 1954 and 1989 was 35,327 at Guerrero Negro-Ojo de Liebre, and 33,278 at San Ignacio. Conservations efforts have been focused on establishing protective laws (Presidential decress created refuges and Biosphere reserve), and controlling hunting and human disturbance. This work discusses the specific conservation requeriments of brant, as well as of the lagoons as an habitat wich worth the preservation of migratory birds.

Appoximately 308 species of terrestial and marine vertebrates (fishes not included) inhabit the reserve. Four of them are amphibians, 43 reptiles, 192 birds and 69 mammals. Only two especies are endemic, the kangaroo rat Dipodomys peninsularis and the squirrel Spermophilus atricapillus. Some other are considered threatened or endangered species.

During 1998 and 1989, 52 species of birds were recorded at San ignacio Lagoon, Baja California Sur, Mexico. Forty-four species were noted at ballena island, in the northern arm of the lagoon. Nine species breed on Ballena Island, including the densest known colony of Ospreys, a significant number of Reddish Egrets, and a large and relatively recently established colonies of Brown Pelicans, Double-crested Cormorants, Great Blue Herons, Western Gulls, and Caspian Terns. In spite of increasing human disturbance, numbers and variety of birds nesting on Ballena Island are evidently greater than 1927.

This guide treats the approximately 1070 species of birds that occur in Mexico (including all islands) and northern Central America.