Responses of birds to planting of Lotus tenuis pasture in the Flooding Pampas, Argentina.

The Flooding Pampas is the most important livestock region of Argentina, but is a region where replacement of originally natural, perennial tussock grasses by pasture species is changing the heterogeneity of the grassland system. We evaluated the response of grassland bird assemblages of the Flooding Pampas to planting of Lotus tenuis (Lotus) pasture, which mainly modifies vegetation structure by reducing vertical heterogeneity. Species richness and abundance of birds were compared between fields of Lotus pasture and semi-natural grasslands. Avian species richness and abundance were both greater in semi-natural grassland than in Lotus pasture. When grouped by nesting habits (grassland specialists, generalists), species richness and abundance of grassland specialists was greater in semi-natural grassland, whereas richness and abundance of generalist species was greater in Lotus pasture. An indicator-species analysis showed that five grassland birds were closely linked to semi-natural grassland vegetation, with two of those species - Hudson's Canastero (Asthenes hudsoni) and Bay-capped Wren-Spinetail (Spartonoica maluroides) - of conservation concern.1 In contrast, generalist species, such as Southern Lapwings (Vanellus chilensis) and Burrowing Owls (Athene cunicularia), were associated with Lotus pasture. Planting of Lotus pasture has negative effects on species that naturally occur in tussock grassland. Grassland management methods, such as intercropping and rotational grazing, could help reconcile the effects of livestock production and the conservation grassland bird conservation in the Flooding Pampas. [ABSTRACT FROM AUTHOR]