Balsas region and interior Oaxaca

Country/Territory Mexico
Area 110,000 km2
Altitude 0 - 2500m
Priority urgent
Habitat loss moderate
Knowledge good

General characteristics

The catchment area of the Balsas river delimits this Mexican EBA and for this purpose extends from Colima state in the west to interior Oaxaca in the east, and to Puebla and Morelos states in the north. The trans-Mexican volcanic range (EBA 006 in part) lies adjacent to the northern boundary of this EBA, and the interior slopes of the Sierra Madre del Sur of Guerrero and the Sierras de Yucuyacua and Miahuatlán in Oaxaca (EBA 009) abut its southern boundary. The altitude varies from sea-level (though most of the EBA is above c.300 m) up to 2,500 m (especially on some of the mountain slopes in the interior of Oaxaca state).

There is a marked dry season of five to eight months in this region, and low annual average rainfall (Rzedowski 1978). The vegetation is consequently dominated by tropical dry deciduous forest, especially at lower altitudes. These dry forests have been noted for their high levels of regional and local endemism in a wide range of taxa, especially cacti (Dinerstein et al. 1995). Other habitats include arid scrub and, at higher altitudes, especially in the interior of Oaxaca, arid oak scrub.

Restricted-range species

All of the restricted-range bird species occur in the dry deciduous and arid scrub habitats, but there are some clear differences in their distributions: Philortyx fasciatus and Aimophila humeralis are confined to the western and central parts of the Balsas drainage and do not occur in Oaxaca; conversely A. notosticta and A. mysticalis are found mainly in interior Oaxaca.

Another possible addition to this EBA is Balsas Screech-owl Otus seductus, confined to the western and central Balsas region. It was listed as a species by Sibley and Monroe (1990), but was later treated as a subspecies of the widespread Western Screech-owl O. kennicottii (Sibley and Monroe 1993). Most of the ranges of Slaty Vireo Vireo brevipennis and Dwarf Vireo V. nelsoni are confined to this EBA, but neither is treated as a restricted-range species because each is judged to breed over an area greater than 50,000 km2.

Species IUCN Category
Banded Quail (Philortyx fasciatus) LC
Dusky Hummingbird (Cynanthus sordidus) LC
Beautiful Hummingbird (Calothorax pulcher) LC
Grey-breasted Woodpecker (Melanerpes hypopolius) LC
Pileated Flycatcher (Xenotriccus mexicanus) LC
San Blas Jay (Cyanocorax sanblasianus) LC
Black-chested Sparrow (Peucaea humeralis) LC
Bridled Sparrow (Peucaea mystacalis) LC
White-throated Towhee (Melozone albicollis) LC
Oaxaca Sparrow (Aimophila notosticta) LC

Important Bird Areas (IBAs)
IBA Code Site Name Country
MX005 Tancítaro Mexico
MX017 Sierra de Taxco-Nevado de Toluca Mexico
MX018 Cañón del Zopilote Mexico
MX019 Acahuizotla - Agua del Obispo Mexico
MX022 Vallecitos de Zaragoza Mexico
MX023 Cuenca Baja del Balsas Mexico
MX024 Lagunas Costeras de Guerrero Mexico
MX025 Coalcomán-Pómaro Mexico
MX026 Valle de Tehuacán-Cuicatlán Mexico
MX028 Tlaxiaco Mexico
MX033 Chamela-Cuitzmala Mexico
MX039 Cañón de Lobos Mexico
MX040 Sierra de Huautla Mexico
MX266 Parque Natural Sierra Nanchititla Mexico
MX268 Cuenca baja del Río Papagayo Mexico

Threat and conservation

The largest remaining dry forests north of the equator, of which this EBA holds a significant amount, are found in western Mexico (Ceballos and García 1995). Most have been affected by human activity; this EBA is no exception, with agricultural expansion, intensive cultivation for export crops, conversion for cattle-ranching, coffee and citrus plantations posing threats to wildlife (Dinerstein et al. 1995). There are very few protected areas within the EBA, but none of the restricted-range species is currently considered threatened as all of them are fairly common in their appropriate habitats (Howell and Webb 1995a).

Recommended citation
BirdLife International (2020) Endemic Bird Areas factsheet: Balsas region and interior Oaxaca. Downloaded from http://www.birdlife.org on 09/07/2020.