This EBA consists of a small number of lake and river marshes, mainly in the Lerma drainage, in the Mexican states of Guanajuato, Michoacán and México. The river drainage falls within the southern end of the Mexican plateau and also in the zone where the plateau merges with the trans-Mexican volcanic range, thus overlapping with the Sierra Madre Occidental and trans-Mexican range (EBA 006), whose restricted-range species are, however, confined primarily to forest habitats.

Around the lake shores and river marshes the habitat comprises cattails and other reedy vegetation, mainly Typha and Scirpus, and to a lesser extent Heleocharis and Cyperus, all of which form dense stands often more than 2 m tall.

This area is designated an EBA because it has one extant and one extinct restricted-range species, both marsh birds. Quiscalus palustris was last recorded in 1910 (Dickerman 1965), and was a resident endemic in marshes at the headwaters of the Lerma river, around Mexico City. Little is known of the species, but it is thought to have been a colonial breeder, nesting in reedbeds (Hardy 1965).

A subspecies of Yellow Rail Coturnicops noveboracensis goldmani is also endemic to the marshes of the Lerma valley. It prefers sedge marshes in ungrazed areas with vegetation less than 0.5 m tall (Hardy and Dickerman 1965). This race may, however, be extinct as it has not been sighted since 1964, but it is skulking and hard to see unless flushed by chance.

The marshes of this EBA have been greatly reduced in size, most having been drained and planted with crops. Water extraction is an additional threat to both lakes and marshes, with the headwaters of the Lerma now supplying México City and Toluca. Thus the water level of the large lakes in the north and west of the EBA (Yuriria, Pátzcuaro and Cuitzeo) in Guanajuato and Michoacán states is falling and affecting the marsh-edge and cattail habitat. The situation is exacerbated because these lakes are old, and are becoming shallower through natural build-up of organic material. The destruction of the marshes is the most likely reason for the demise of Quiscalus palustris, and for the threatened status of Geothlypis speciosa.

Four Key Areas have been identified by Wege and Long (1995) for the protection of G. speciosa: the three lakes listed above and the region of the upper Lerma around Lerma da Villada, San Mateo Atenco and San Pedro Techuchuco. The best populations of the species appear to be at Lago Cuitzeo, where it is apparently quite abundant (in the 1980s, three times as numerous as Common Yellowthroat G. trichas), and on the upper Lerma, where it has been described as fairly common. However, the population has not been censused in either area in the 1990s, and the marsh habitat probably continues to decline. Drainage in the upper Lerma has left the marshes highly fragmented, and the effect of this on yellowthroat populations is unknown. There are no protected areas within this EBA, and no conservation measures for the yellowthroat are known.

Recommended citation
BirdLife International (2024) Endemic Bird Area factsheet: Central Mexican marshes. Downloaded from https://datazone.birdlife.org/eba/factsheet/8 on 23/11/2024.