Diversity patterns of bird assemblages in arid zones of northern Venezuela

Abstract

In northern Venezuela, arid zones are represented by isolated areas, which are important from an ornithological perspective because of the occurrence of restricted-range birds, which depend exclusively on arid scrub for their survival. From September 2004 to August 2005, bird surveys were conducted bimonthly using distance sampling at point counts in six areas of northern Venezuela, which differ in size and geological origin. A total of 21 228 individuals representing 96 species and 26 families were recorded throughout the study areas. Bird species richness, community composition, and species abundance varied among areas. Number of species recorded per area ranged from 37 to 82. An analysis of similarity showed that areas differed in overall community composition based on species presence or absence (Global R = 0.68). The Vermilion Cardinal (Cardinalis phoeniceus) was the only restricted-range species with a high indicator value (52%) identified through an indicator species analysis. The most abundant birds in all six areas were widespread generalist species, such as the Tropical Mockingbird (Mimus gilvus) and Tropical Gnatcatcher (Polioptila plumbea), and only one of the restricted-range birds, the Buffy Hummingbird (Leucippus fallax), had high densities (range: 2.67-9.00 individuals ha-1) throughout all the study areas. Densities of two restricted-range birds, the Yellow-shouldered Parrot (Amazona barbadensis) and Vermilion Cardinal varied among areas as a consequence of poaching in some areas. Species richness was not a reliable indicator of an area's conservation value because the protection of the area with highest species richness does not guarantee the effective conservation of all the restricted-range birds. © The Cooper Ornithological Society 2008.