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Birds of the Tambo Area, an Arid Valley in the Bolivian Andes

1997; Issue: 48 Linguagem: Inglês

10.2307/40157561

1941-2282

C. Gregory Schmitt, Donna C. Schmitt, J. V. Remsen,

Species Distribution and Climate Change

We surveyed birds in an arid valley at 1,500 m elevation in the Andes of western depto. Santa Cruz, Bolivia, in January and February, and in June and July. This is one of the only localities with xeric vegetation to be surveyed in an arid intermontane valley of the Eastern Andes. The 50 species breeding or presumed to be breeding in the arid scrub provides a striking example of high species richness at tropical latitudes. Differences between the surveys in January-February (summer wet season) and the one in June (winter dry season) show strong seasonality in the presence/ absence or abundance in 32 of the 92 regularly occurring species. Whereas at least 5 1 species were breeding or probably breeding during the January-February surveys, only five were breeding or probably breeding during the June-July survey. Subcutaneous levels were scored as no fat or low in 95% of all individuals collected. Most species occurring at this Andean locality have primarily lowland, rather than Andean, geographic distributions. Resumen. Investigamos las aves en un valle arido a 1,500 m de altura en los Andes al oeste del Departamento de Santa Cruz, Bolivia, en Enero y Febrero, y en Junio y Julio. Esta es una de las unicas localidades con vegetaci6n xerofitica a ser investigadas en un valle arido intermontano en los Andes Orientales. Las 50 especies que se reproducen o que se presume que se reproducen en arbustos aridos nos da un notable ejemplo de una gran riqueza de especies en latitudes tropicales. Las differencies entre las investigaciones en Enero-Febrero (verano estaci6n humeda) y la de Junio (invierno estaci6n seca) muestran una fuerte estacionalidad en la presencia/ausencia o abundancia en 32 de las 92 especies que regularmente estin presentes. Considerando que por lo menos 51 especies se estaban reproduciendo o probablemente reproduciendo durante la investigaci6n de Enero-Febrero, solamente seis se estaban reproduciendo o probablemente reproduciendo durante la investigaci6n de Junio-Julio. Los niveles de subcutanea fueron calificados como sin grasa o bajo en 95% de todos los individuos colectados. La mayoria de las especies que ocurren en esta localidad andina tienen primordialmente distribuci6n geogrf O'Neill 1992). Other intermontane Andean valleys that do not transect the Eastern Andes have been studied by Miller (1947, 1952). Although also rich in endemic bird taxa and important as a biogeographic barrier, the Rio Grande Valley of central Bolivia has received less attention. This dry, intermontane valley system forms a major barrier to dispersal for humid forest birds of the Andes, few of which occur south of the Rfo Grande Valley (Remsen et al. 1986, 1987). Within the valley, a mosaic of vegetation types ranges from semi-humid forest to barren scrub. The Rfo Grande Valley has been disturbed heavily by humans, and so the character of the original vegetation is unknown. Two bird species are endemic to the valley system: Ara rubrogenys (Red-fronted Macaw) and Poospiza garleppi (Cochabamba Mountain-Finch); five other species whose main distribution is the Rfo Grande Valley system but which also occur in the nearby Rio La Paz or Rfo Pilcomayo valleys are: Oreotrochilus adela (Wedge-tailed Hillstar), Upucerthia harterti (Bolivian Earthcreeper), Sicalis