SummaryIn this study I present data suggesting altitudinal movements of some species of foliage-gleaning insectivorous birds and related species of an oak-pine woodland of western Mexico. These movements can be regarded as short-distance or local migrations because the species involved breed in the woodlands and forests of the Sierra Madre Occidental highlands and winter in the tropical forests of the Pacific lowlands. Nine species of insectivorous birds out of 17 breed at the study site in the mountains of southern Durango and move to the lowlands in the winter; these can be regarded as short-distance or local migrants. In Mexico tropical deciduous and semi-deciduous forests are distributed mostly in the Pacific lowlands in the states of Sinaloa, Durango, Nayarit and Jalisco. Tropical forests of the Pacific lowlands are very important as wintering grounds for both North American and local west-Mexican migrants; however, there is only one protected area in western Mexico which to some degree includes these two types of tropical forests, and it is not located in the Sierra Madre Occidental, the most important mountain range in Mexico in terms of length and area covered. In addition, these tropical forests are the northern limit of the range for many tropical species. At present, these habitats are not threatened seriously by human activities (mainly forestry and cattle-raising) but this might change at any moment. At the study site the temperate highlands of southern Durango are already under the protection of “La Michilía” Biosphere Reserve, but a proposal to enlarge the area of the reserve to include the valley of the Río Mezquital and the western slope of the valley will increase the diversity of habitats, both temperate and tropical. As a consequence more bird species, as well as other taxa, will be protected in their natural environments. Such a proposal must be supported by field evidence on actual habitat use both during the breeding and wintering season, by local and long-distance migrants, in order to assess accurately the importance of this area as a representative place of western Mexico.
Ignimbrite flare-up and deformation in the southern Sierra Madre Occidental, western Mexico: Implications for the late subduction history of the Farallon plate