Several mountain ranges in southern Oaxaca and southern Guerrero states of Mexico together form the Sierra Madre del Sur. The isolated Sierra de Miahuatlán in southern Oaxaca is the easternmost part of the Sierra Madre del Sur. To the west and further inland the Sierra de Yucuyacua straddles the Oaxaca and Guerrero state boundaries. The Sierra de Atoyac continues through Guerrero to the Balsas valley, which marks the western limits of the EBA. Inland and on the lower Gulf slopes of these mountain ranges lie the arid lands of the Balsas region and interior Oaxaca (EBA 008).

The principal habitats of the EBA are various types of humid montane and lower montane forests. The dominant vegetation is lower montane (semi-deciduous) forest from 600 to 1,400 m, humid montane and cloud forest on the wettest slopes between 1,400 and 2,500 m, pine oak forest at 2,500-3,000 m, and fir forest at altitudes above 3,000 m (Navarro 1992). On drier exposed slopes the vegetation is more arid, with oak scrub predominant. The montane forest found partly within this EBA represents some of the world’s most diverse and complex subtropical mixed hardwood-conifer forests (WWF/IUCN 1997).

The restricted-range birds are found mainly in humid montane forest consisting of many evergreen tree species, especially oaks, with variable amounts of pine at higher altitudes. Because the altitudinal ranges of particular forest types vary according to the local topography and climate, the restricted-range species appear to show quite wide altitudinal preferences.

Lophornis brachylopha is still known from only a single 25-km stretch of the Atoyac-Paraíso-Puerto el Gallo road in the Sierra de Atoyac (north-west of Acapulco), and is likely to be confined to the Sierra Madre del Sur within Guerrero. The species has been found to be common only seasonally, which suggests that it may undergo altitudinal movements to an unknown area and habitat. The Sierra de Atoyac is also the type-locality of the recently described Cypseloides storeri (Navarro et al. 1992), which has subsequently been recorded also in Michoacán and Jalisco in the trans-Mexican range (EBA 006 in part); little information is available on this bird, and its status as a resident within the Sierra Madre del Sur is unknown.

Of the remaining restricted-range birds, the two Eupherusa species are allopatric, E. poliocerca being confined to the Sierras de Atoyac and Yucuyacua, E. cyanophrys to the Sierra de Miahuatlán. Cyanolyca mirabilis is the only restricted-range species to be found in all three sierras.

Many of the forests of these mountains are being cleared for large-scale agricultural expansion or for timber, and it has been suggested that all are in danger of complete destruction (Navarro 1992). The lower montane forest is being cleared for corn, fruit (notably citrus fruits in the Sierra de Miahuatlán: Dinerstein et al. 1995) and coffee; the cloud forests below 1,800 m are being destroyed for coffee plantations; and the pine, oak and fir forests are being cut for lumber (Navarro 1992). With habitat destruction continuing rapidly, all four of the restricted-range species confined to this EBA are considered to be highly threatened.

There is just one protected area within this EBA, Omiltemi State Ecological Park (96 km²) lying in the Sierra de Atoyac c.20 km west of Chilpancingo in Guerrero; it supports populations of Eupherusa poliocerca and Cyanolyca mirabilis (ICBP 1992, Navarro and Escalante Pliego 1993). The other two threatened species remain unprotected, and at least two new protected areas need to be created in the Sierras de Atoyac and Miahuatlán to support these birds in reserves.

Recommended citation
BirdLife International (2024) Endemic Bird Area factsheet: Sierra Madre del Sur. Downloaded from https://datazone.birdlife.org/eba/factsheet/12 on 23/11/2024.