The Isthmus de Tehuantepec is the part of southern Mexico in the states of eastern Veracruz, eastern Oaxaca and south-west Chiapas where the continental landmass constricts to its minimum width, the distance between the Pacific and Atlantic Oceans being only 210 km. This EBA covers the Pacific Ocean/Gulf of Tehuantepec side of the isthmus in south-east Oaxaca and south-west Chiapas, including the coastal plain (the Plains of Tehuantepec) and the low-lying hills and isolated peaks to 1,000 m altitude.

The western boundary of the EBA is marked by the basin of the Tehuantepec river, and the eastern end lies along the coastal plain near Tonala, which also marks the northern end of the North Central American Pacific slope (EBA 017). The landward northern boundary of the EBA falls along the Sierra Atrevesada, a small, low-lying range stretching for 50 km, and the Sierra Madre de Chiapas, which is the western end of the North Central American highlands (EBA 018). The southern coastal side falls alongside several large coastal lagoons, including Lagunas Superior, Inferior and Mar Muerto.

The main habitats in the coastal plain of this EBA are deciduous forest, semi-deciduous gallery forest and arid scrub, in the foothills also arid pine-oak forest.

Two of this EBA's three restricted-range bird species are confined to it, while Aratinga strenua occurs also further south in Central America (EBA 017). A. strenua is very closely related to the widespread Green Parakeet A. holochlora , and Binford (1989) prefers to treat them as conspecific because there are two specimens known with measurements intermediate between the two taxa.

The habitat requirements of Aratinga strenua and Aimophila sumichrasti are quite similar, both species preferring open areas in tropical deciduous forest and arid tropical scrub from sea-level to 1,000 m. Passerina rositae inhabits the riparian forest and denser portions of tropical deciduous forest, mainly from 200 to 500 m elevation (Binford 1989).

The Pan-American Highway runs through the entire length of the EBA. Consequently the dry forests are quite fragmented and many of them are degraded or secondary. However, none of the restricted-range species is currently considered threatened, as, although Passerina rositae and Aimophila sumichrasti clearly have very small ranges, both are considered to be common in their appropriate habitats, including areas altered by man (Binford 1989, Howell and Webb 1995a).

The Chiapan part of the EBA is almost entirely covered by La Sepultura Biosphere Reserve, which was designated by presidential decree as recently as 1995. It comprises five core areas totalling 138 km² and a buffer area of 1,536 km ² (A. Flamenco in litt. 1995).

Recommended citation
BirdLife International (2024) Endemic Bird Area factsheet: Isthmus of Tehuantepec. Downloaded from https://datazone.birdlife.org/eba/factsheet/13 on 23/11/2024.