Specific Limits and Distribution of Meadowlarks of the Desert Grassland

Abstract

THE polytypic Eastern Meadowlark (Sturnella magna) has a breeding range that extends throughout eastern North America westward to Ontario, Nebraska, Texas, and Arizona, and southward through Central and South America as far as northern Brazil. A monotypic sibling species, the Western Meadowlark (Sturnella neglecta), breeds only in western North America eastward to the Great Lakes region, Missouri, and Texas, and southward on the Mexican plateau to northern Jalisco. A poorly differentiated northwestern race, S. neglecta confluenta, is currently recognized by the A.O.U. Check-list (1957). The breeding ranges of these species overlap broadly throughout the north-central United States, from Oklahoma northeastward into Ontario. Their behavioral and ecological interrelationships within this zone of sympatry have been described elsewhere (Lanyon, 1953, 1956, 1957). A similar analysis of their sympatric relationship in the southwestern United States and in Mexico has been delayed because of the (1) considerable confusion that exists even among contemporary ornithologists as to the specific identification of the meadowlarks breeding in these regions and, owing to this confusion, (2) a lack of reliable distributional data for these areas. The Mexican Check-list states, for example, that the southern limits of the breeding ranges of S. neglecta and S. magna lilianae are not known (Miller et al., 1957). The objectives of this paper are (1) to present the specific limits for those populations of the two species that are involved in the area of geographical overlap in the southwestern United States and Mexico, and (2) to summarize the distributional data for this area based on a reexamination of the material currently available. A preliminary discussion of their ecological relationships in this zone is included. A map of the breeding ranges of the populations under consideration here is presented in Figure 1. On the basis of evidence reviewed during this study, the current taxonomic treatment of the breeding populations within the area of geographical overlap in the southwestern United States and in Mexico appears adequate (Miller et al., 1957), with two races of magna and the monotypic neglecta involved. The breeding ranges of the three races appear to be as follows (cf. Figure 1): (1) Sturnella magna lilianae Oberholser breeds from north-central Arizona east to central eastern New Mexico and south to northern Sonora, Chihuahua, and the Big Bend region of Texas; (2) S. magna auropectoralis Saunders breeds from Sinaloa and central Durango southward, intergrading with S. m. alticola south of the area of sympatry;