Individual study: Effect of shrub removal on bird community composition in degraded Chaco woodland at Estación Experimental La Marê, Santiago del Estero, Argentina
Codesido M., Drozd A.A., Gado P.A. & Bilenca D. (2009) Respuestas de un ensamble de aves a la remoción manual de arbustos en un bosque subtropical semiÃ¡rido del Chaco argentino [Responses of a bird assemblage to manual shrub removal in a Chacoan subtropical semiarid forest, Argentina]. Ornitologê Neotropical, 20, 47-60
Logging and the introduction of domestic cattle have resulted in the transformation of much of the semi-arid woodlands of the Argentinean Chaco from tall forest to dense, shrubby scrubland. This study investigated the medium-term effect of manual removal of shrubs (one technique used to restore forest structure) on the diversity and composition of the bird community in degraded woodland at Estación Experimental La María (28°03'S, 64°15'W), Santiago del Estero, northern Argentina.
In 1991, shrubs were manually removed from a 200-ha area of the study site (‘treatment area’), taking care to preserve saplings of species that form part of the tree layer (i.e. Aspidosperma quebracho-blanco, Schinopsis lorentzii, Prosopis nigra and Zizyphus mistol). A second area (also 200 ha) nearby, with similar characteristics to the treatment area, was left unmanipulated, as a control.
During 1998–1999, the treatment and control areas were surveyed for birds four times: in March (i.e. end of austral summer) 1998; August (i.e. winter) 1998; December (i.e. late spring) 1998; and August 1999. During each survey period, 30 point counts were carried out within each area. For the purposes of analysis, all species recorded were allocated to one of 10 foraging guilds, based on their diet, microhabitat and foraging technique.
In total, 69 bird species were recorded during surveys of the two study areas. Overall, there was no significant difference in bird abundance or species richness between the treatment and control areas, but during the late summer 1998 the treatment area contained significantly fewer species (and individuals) than the control area.
Of the 10 foraging guilds considered, three showed a significant difference in overall abundance between treatment and control areas. Bark-feeding insectivores (e.g. green-barred woodpecker Colaptes melanochloros and narrow-billed woodcreeper Lepidocolaptes angustirostris) were significantly more abundant in the treatment area. In contrast, foliage-gleaning insectivores (e.g. stripe-crowned spinetail Cranioleuca pyrrhophia and variable antshrike Thamnophilus caerulescens) and arboreal seed-eating species (e.g. monk parakeet Myiopsitta monachus and golden-billed saltator Saltator aurantiirostris) were significantly less abundant in the treatment area. In addition, during December 1998, terrestrial insectivores were significantly less abundant in the treatment than the control area.
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