The Cattle Egret in Central Baja California, México

Abstract

The Cattle Egret (Bubulcus ibis) now seems to be established in northern and western M6xico. Zimmerman (Condor 75:480, 1973) reported numerous sightings in Coahuila in 1971 and 1972, and in Chihuahua, Nuevo Le6n, and San Luis Potosi in 1972. On the western mainland the Cattle Egret was reported in Sinaloa (Alden, Finding the birds in western Mexico, Univ. Arizona Press, 1969) and Guerrero (Dickerman, Wilson Bull. 76:290, 1964) in 1964, and in Chiapas (Hubbard, Wilson Bull. 78: 121, 1966) in 1965. Other records also exist (Hubbs Condor 70:92, 1968). In Baja California the only records we are aware of are those of Hubbs. One, near the southeastern extremity of the peninsula, is a sight record by A. J. Sloan who, in 1964, found the species in a mangrove lagoon near the south end of Isla San Jose, in the Golfo de California. The other was based on a newspaper photograph which showed a lone Cattle Egret onboard a sport fishing boat off northwestern Baja California near Punta San Isidro in 1967. The nature of these records and the importance of documenting the occurrence of the Cattle Egret for studies on the dynamics of range expansions prompt us to report our observations of this species in Baja California. On 8 May 1973, while working in the vicinity of Guerrero Negro, Baja California Sur, midway down the Pacific coast of the peninsula, we observed three Cattle Egrets feeding in a dry, scrubby field adjacent to a canal. On 9 May, a flock of at least five was seen in a similar habitat and one female was obtained. This specimen is now in the Santa Barbara Museum of Natural History and bears the following information: SBMNH 2366; wt. 380 g; bill orangeyellow, irides yellow, tibiotarsus mostly yellow, tarsometatarsus and feet black; largest ovum 2 mm; stomach contained several grasshoppers, two lizards (Uta stansburiana, 135 mm long; Sceloporus sp., 155 mm), and one lizard tail. Most of Baja California is arid and sparsely populated. The area around Guerrero Negro, however, is lowland adjacent to Scammon's Lagoon and has isolated mangrove swamps, Salicornia salt marshes, and canals leading to man-made embayments. No domestic animals were seen. The reproductive condition of the specimen we obtained suggests that these egrets may have been stragglers in that region. Even though the first observation of the Cattle Egret off western Baja California was made five years earlier than ours, there is no indication that the species is now established on the peninsula. We did not see other Bubulcus ibis during May 1973, while working in coastal marshes and lowland habitat near La Paz (5 May), Muleg6 (6, 7, 11, and 12 May), San Ignacio (10 May), Magdalena Bay (13 and 14 May), Bahia San Quintin (21 and 22 May), and south of Mexicali (23 May). Throughout our stay in Baja California we were accompanied and aided by Jos6 Torres Ayala and Felipe Viramontes V., students at the Universidad de Nuevo Le6n, Monterrey; we are also indebted to Arturo Jimenez G. of that Universidad.