Although several researchers have studied birds in the state of Sonora, Mexico, few published reports exist. Van Rossem (1945) published the only comprehensive summary, now outdated. Recently, Everett and Anderson (1991) addressed the status of the breeding seabirds of the Gulf of California.
The northernmost of Sonora’s large lagoons is Bahía San Jorge, with its associated Estero San Francisquito and islands (Figure 1). Bahía San Jorge is a large bay separated from the open gulf by a long (10 km) sand bar on its southern side. Estero San Francisquito, a long, narrow tidal estuary, lies immediately to the south. Except for marshes inside the southern part of the bay, dunes are the principal terrestrial habitats around Bahía San Jorge. Certain areas are open flats with shell debris. Bahía San Jorge and Estero San Francisquito have not been investigated ornithologically in any detail, like the rest of the northern Sonora coast, with the exception of Puerto Peñasco, a popular destination for North American birdwatchers, reported on by Huey (1935) and Janes and Janes (1987).