Habitat mosaic and understory bird communities in Mexican cloud forest

Cloud forest is one of the most threatened ecosystems in Mexico and is important for its high biological diversity and for the ecological services that it provides. The Mexican cloud forests (CF) have been fragmented as a result of anthropogenic activities and deforestation. The south of Mexico contains almost 30% of the country's cloud forest, only a small proportion of which is protected in nature reserves. Conservation effort needs to be focused on the ecological value of agroecosystems that surround nature reserves. The study areas are located in the south of Mexico. Two are in the El Triunfo biosphera reserve in la Sierra Madre de Chiapas, and one is located in the central Region Mountains of Veracruz. The coffee is cultivated in transitional areas between natural forest and adjoining land systems. Based on the type of management, the structure and vegetation, it is possible to distinguish five main coffee production systems: two traditional shaded agroforests (with native trees), one commercially oriented polyspecific shaded system (where several fruit trees are used as shade), and two "modern" systems shaded (Inga) and unshaded monocultures (sun coffee). This research attempts to explain the effects of cloud forest patches (natural forest and coffee plantations) on bird diversity.

Bird communities have been surveyed in 4 habitat types by point counts and mist-net techniques. The surveys were taken across a gradient from extensive primary and relatively undisturbed forest to intensive agricultural land uses (coffee plantations). Patterns of bird populations (species richness, abundance, density and community composition) and patch characteristics (size, altitudinal range, and topographic complexity) were analysed over this gradient.

Of a total of 4560 birds recorded in point counts, there were 294 species, 168 genera and 41 families. In the patches of CF, from a total of 256 bird species, 36 were migratory and 53 have some status of conservation. In the patches of coffee plantations from a total of 159 species, 49 were migratory and 52 were under some status of conservation. Forest habitats, including continuous and patch forests, and shade coffee plantations, are found to support the most species and individuals. Nearctic-Neotropical migratory species are most numerous in shade coffee. Bird communities in shade coffee (natural and Inga) are characterised by a higher proportion of frugivorous and nectarivorous species, than communities in native forests. Using mist-net techniques, a total of 105 species, 87 genera and 23 families of birds were captured in 1600 net/hours for all the habitats.

The size of forest patch is the main characteristic affecting forest interior and generalist species. Decreasing forest patch sizes appears to have unfavourable effects on forest generalist birds and positive effects on forest border species. The bird species most sensitive to forest fragmentation are those species restricted to the forest interior. The species richness and abundance demonstrate that many human-altered habitats are potentially valuable for birds. Further conservation efforts in tropical areas need to give more attention to the significance of agricultural lands as wildlife habitats.