Arroyos as Winter Habitat
By Gregory Gough
The clearing of forests in the tropics has a been a cause of some concern for scientists worried about the loss of habitat for both resident and migratory birds. A study in Mexico near the Guatemalan border revealed that arroyos can provide a refuge for birds.
Arroyos, or wooded patches along streams and rivers, are typically left behind as the surrounding land is cleared for agriculture. Some arroyos consist of remnant forest, others of scrub, and others of woods with or without an understory. All appealed to birds, with the understory-free forest, cleared for cattle, being the least appealing.
Study sites consisted of arroyos that were 10 years old and those that were 35 years old. There was no difference in the bird community between the two ages so even fairly recently cleared agricultural areas can provide habitat for birds if the arroyos are left intact.
This article summarizes the information in this publication:
Warkentin, I., Greenberg, R.S. and Salgado Ortiz, J. 1995. Songbird use of gallery woodland in recently cleared and older settled landscapes of the Selva Lacandona, Chiapas, Mexico. Conservation Biology, 5: 1095-1106.
Many regions of Central America have undergone wide-scale habitat change as land has been converted for cultivation or grazing. Clearing for agriculture often leaves a variety of regenerating and remnant patches of wooded vegetation. Of particular importance is arroyo vegetation, or strips of trees or tall shrubs growing along streams. Although it is widely acknowledged that tropical arroyo vegetation supports high densities of birds, as avian habitat it remains poorly studied. We used point counts to study populations of migrant and resident songbirds in the arroyo vegetation of settled areas of the Selva Lacandona adjacent to the Montes Azules Biosphere Reserve of southeastern Mexico. Two study areas were established on lands that had been cleared and settled 20-35 and 10 years previously. Our objectives were to assess the value ofarroyo vegetation to the conservation of avian species diversity and abundance in agricultural landscapes and to compare the composition and abundance ofsongbirds in cleared areas settled at different times over a 35-year period. Arroyo vegetation had a wide diversity of songbird species that, in overall terms, differed little between those landscapes cleared recently and those cleared up to 35 years previously. In both areas we found a high abundance of habitat generalists and a smaller number of forest-dependent species, particularly migrants. Loss of forest specialists occurs rapidly, with little further loss as the arroyos become increasingly isolated. Our data also suggest that birds do not crowd into limited habitat as the surrounding vegetation is eliminated, implying that the overall carrying capacity of the agricultural landscape is greatly enhanced as larger areas of arroyo vegetation areprotected. Protection of arroyo vegetation will increase the diversity of birds living in agricultural areas and can be achieved simply by expanding upon land-use practices currently in use.
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