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Article Excerpt
Abstract.-Riparian areas have been identified as key habitats for wildlife, especially for the North American arid landscape; however, similar areas in northern Mexico have been poorly studied. This study was conducted in a riparian habitat dominated by Montezuma bald cypresses (Taxodium mucronatum) of the Rio Sabinas, Coahuila, Mexico, from December 2004 to November 2005. Monthly samples were conducted, using a total of 443 point counts, in three river sections characterized by distinct levels of disturbance, from lesser to greater: Melchor Muzquiz, San Juan de Sabinas and Sabinas. A total of 168 species were recorded. The Melchor Muzquiz section exhibited the smallest number of species corrected by rarefaction and a significantly smaller number of species and individuals per point count. The Olmstead-Tukey diagrams per section also showed differences in the dominance of the species. From a conservation point of view, noteworthy species were recorded such as Wood Stork and Painted Bunting.
Resumen.-Las zonas riberenas han sido identificadas como habitats clave para la vida silvestre, especialmente para el paisaje arido de Norteamerica; sin embargo en el norte de Mexico dichas zonas han sido poco estudiadas. El presente estudio se llevo a cabo en el habitat ribereno dominado por sabinos (Taxodium mucronatum) del Rio Sabinas, Coahuila, Mexico, de diciembre de 2004 a noviembre de 2005. Se llevaron a cabo muestreos mensuales utilizando un total de 443 puntos de conteo de radio fijo en tres zonas del rio caracterizadas por distintos niveles de disturbio, de menor a mayor: Melchor Muzquiz, San Juan de Sabinas y Sabinas. Se registraron un total de 168 especies. La zona Melchor Muzquiz mostro el menor numero de especies corregidas por rarefacction y un numero significativamente menor de especies e individuos por punto de conteo. Los diagramas Olmstead-Tukey por zona tambien mostraron diferencias en la dominancia de las especies. Se registraron especies importantes desde el punto de vista de la conservation, como Mycteria americana y Passerina ciris.
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The importance of riparian zones for breeding and migrant birds has been extensively documented (e. g., Knopf et al. 1988; Knopf & Samson 1994; Skagen et al. 1998; Anthony et al. 1996; Finch & Yong 2000; Flannery et al. 2004; Kelly & Hutto 2005; Villasenor 2006). While riparian woodlands of North America constitute less than 1% of the area of arid landscapes they support more reproductive birds than the extensive surroundings (e.g., Knopf et al. 1988). Unfortunately, it has been suggested that at least 95% of all western riparian habitats have been altered in some way during the past century (Ohmart 1994), and that such destruction may be the most important factor in the decline of some western North American landbird species during the past century (DeSante & George 1994). However, the effects of such alterations on riparian systems may be unnoticed for decades due to longevity of cottonwoods (Rood & Mahoney 1993) and other riparian trees such as Montezuma bald cypresses. This could cause a delay in awareness of the need for conservation, management, and restoration actions.
In northwestern Mexico, there have been few studies conducted on the importance of riparian habitats for migratory birds (Hutto 1995; Villasenor 2006), but none in the northeastern portion. The Rio Sabinas (130 km length) is located in northeastern Coahuila, running from the Sierra Santa Rosa near Melchor Muzquiz to the Venustiano Carranza Dam near Juarez municipality (Fig. 1). Its avifauna has been little studied even though it is a Priority Terrestrial Region for Conservation in Mexico (RTP-152, Arriaga et al. 2000), a State Natural Protected Area (Periodico Oficial 1998), and an important biological corridor linking northern Mexico with the southern United States through the well-conserved Sierra Santa Rosa, Maderas del Carmen and Big Bend National Park. This connection is also maintained downstream from the Venustiano Carranza Dam where the river is named the Rio Salado; it flows through Nuevo Leon and Tamaulipas and enters the Falcon Reservoir which is part of the Rio Grande. Its riparian vegetation is dominated by Montezuma bald cypress (Taxodium mucronatum, locally known as "sabino"), while pecan (Carya illinoinensis), sycamore (Platanus occidentalis), sugar hackberry (Celtis laevigata), and Mexican ash (Fraxinus berlanderiana) are also present. Its shrub stratum is variable but includes spiny hackberry (C. pallida), huisache (Acacia farnesiana), catclaw (A. greggii), blackbrush (A. rigidula), honey mesquite (Prosopis glandulosa), Texas persimmon (Dyospiros texana), and Mexican mulberry (Morus celtidifolia). The herbaceous cover is composed principally of straggler daisy (Calyptocarpus vialis).
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This area faces serious conservation issues such as lack of biological knowledge, overgrazing, deforestation, and open-ceiling coal mining. The latter is especially harmful because it drastically modifies the environment and frequently breaks into the freatic mantle and extracts water (sometimes from very near the river: Trevino-Garza et al. 2002), affecting the hydrologic dynamics of the basin and interrupting the water flow in some sections of the river. Three distinct sections are observed in the riparian habitat qualitatively characterized by different levels of disturbance. The Melchor Muzquiz (MM) municipality section has a well preserved riparian habitat with mature and young woodland patches; the San Juan de Sabinas (SJS) municipality section contains partially preserved habitat, with mature patches but several rural and urban localities; and the Sabinas (S) municipality section has deteriorated and fragmented riparian woodland vegetation in a narrow corridor which includes dead bald cypresses (due to coal mining activities). Therefore, the objectives of this study were to characterize the bird community of the Rio Sabinas and compare communities among sections with different levels of disturbance.
METHODS
A systematic sampling of birds was conducted from December 2004 to November 2005 along the Rio Sabinas, in localities where Montezuma bald cypresses were present near the municipalities of Melchor Muzquiz (MM), San Juan de Sabinas (SJS) and Sabinas (S). Sections were visited monthly on a rotating basis to obtain a balanced sampling design. A total of 443 point counts (10 min, 25 m radius: Ralph et al. 1996) in 247 randomly selected sites were sampled, covering an area of 34.5 ha and 64 km of river length (approximately 50% of the total). Point counts were conducted by a single observer to reduce bias in detectability. The area was visited from December 2005 to January 2006 and May to August 2006, adding new records to the check-list. Species, including common and scientific...
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