Mexico and Wintering Birds
The idea—In an effort to understand the importance of cottonwood bottomlands on wintering birds in Sonora, Mexico, Fernando Villaseñor designed (in 2003) a companion study to our work in Montana. This research was part of the larger Western North American Migratory Landbird Project, coordinated by Sonoran Joint Venture, which is an international effort to conserve Neotropical migratory birds and their habitats throughout western North America.
Methods—Between 2004 and 2006, Fernando and his crew conducted 1,816 10-minute point counts at 87 locations in 14 major vegetation types throughout Sonora, Mexico. Eighty percent of 253 species they detected were in riparian vegetation, and 72% were detected in non-riparian vegetation. More importantly, riparian bird communities were significantly different than those in non-riparian vegetation and 22% of species that comprise the regional avifauna were restricted to riparian vegetation in winter, which is more than any other vegetation type.
Results—Mean number of species and individuals per count did not vary with the degree of vegetation disturbance. Moreover, mean body condition (body mass/wing cord) of ten species that were the focus of an intensive mist-netting effort, was not affected by vegetation disturbance conditions, but the ratio of blood heterophils to lymphocytes (a index of stress) was significantly higher in 4 of 5 species, suggesting that disturbance degrades the quality of overwintering habitat. For more information about this study contact Fernando, who completed his Ph.D. here in 2006 and is currently a Professor at the Universidad Michoacana de San Nicolás de Hidalgo in Morelia, Mexico.
The idea—Aaron Flesch is currently assessing the distribution, abundance, and habitat use of birds throughout the Madrean Sky Islands of Sonora, with support from the U.S. National Park Service, Comisión Nacional de Áreas Naturales Protegidas (e.g. Mexican National Park Service), and Sky Island Alliance. The Sky Islands are a series of discrete mountain ranges at the northern end of the Sierra Madre Occidental where species of both Nearctic and Neotropical affinities converge. These mountains are called Sky Islands because they support isolated stands of montane vegetation of pines and oaks that rise up out of lowland “seas” of desertscrub and grassland. Although the Sky Islands of Sonora are ecologically unique and world renowned, bird communities in the region have not been studied systematically for decades.
Methods—In 2009 Aaron and his field crew surveyed 70.4 km of point transects between 1,180 and 2,470 m elevation in six Sky Islands, the Sierra las Avispas, Elenita, Mariquita, Opusera, Madera, and Tigre. In 2010 we more than doubled our efforts from 2009 by surveying 447 stations along 63 transects in ten Sky Islands, the Sierra Juriquipa, Purica, el Humo, Cibuta, Azul, los Ajos, el Tigre, Chivato, San Jose, and Cucurpe.
The idea—Ferruginous Pygmy-Owls are endangered in southern Arizona and declining in nearby northern Sonora, Mexico, where they are still locally common. Since 2000, Aaron has monitored abundance, territory occupancy, reproductive performance, and juvenile survival across a 25,000 km sq. region in the Sonoran Desert just south of the Sonora-Arizona border. The goal is to understand what constitutes suitable habitat for pygmy-owls, the degree to which habitat suitability explains patterns of patch occupancy, and how landscape-level factors affect dispersal and, thereby, the theoretical expectation that more suitable patches of habitat are occupied more consistently over time.
Methods—Aaron conducts intensive tracking of radio-marked juveniles, and then evaluates the characteristics of lands used and avoided.
Results—Vegetation disturbance in the matrix surrounding habitat patches affects movement behavior and reduces colonization success of pygmy-owls [link to pdf].