Migrant bird stopover ecology and resident species loss in a fragmented tropical landscape, the Sierra de los Tuxtlas, Veracruz, Mexico

Abstract

I conducted two studies of avian ecology over the course of two spring field seasons (2003, 2004) in the Sierra de Los Tuxtlas, Veracruz, Mexico. I examined mass gains in spring Nearctic-Neotropic migrants at a stopover site near the Estacion de Biologia Tropical Los Tuxtlas. Birds were captured using mist nets. A condition index (mass/wing chord) was calculated for each individual and regressed against time of day to determine if a net gain in condition occurred at the site. Seven of 13 taxa examined showed significant gains in body condition. The average individual of none of these species carried sufficient fat to complete a trans-gulf migration from Los Tuxtlas. Additionally, I studied the loss of resident bird species from the fragment of forest at the Biological Station. I used mist net data acquired over 8 non-breeding seasons from 1973-2004 to determine which taxa have been extirpated as the surrounding landscape became increasingly deforested. Seventeen species of birds prone to capture in mist nets have either disappeared from the station or are showing significant declines in numbers. Data indicate a continuing loss of species from the site, showing the station is not sufficient to maintain the full historic complement of birds species native to Los Tuxtlas.