Livestock indirectly decrease nest abundance of two shrub-nesting species in Patagonian Monte Desert

Abstract

Domestic livestock may indirectly affect bird species through changes in vegetation structure (e.g. cover), reducing the availability of food, nesting sites, refugia and, therefore, reproduction in many ecosystems worldwide. However, it remains unclear how the effect of livestock on vegetation structure can influence insectivorous birds that use shrubs for nest construction and placement rather than for feeding. Several species from the Furnariidae family inhabit Monte Desert, Argentina, exhibiting an extraordinary diversity in nest placement and structure that allows them to survive habitat aridity. Nest abundance and size of two common furnariid species, Pseudoseisura gutturalis and Leptasthenura aegithaloides, were studied across a cumulative livestock impact gradient (livestock impact by years grazed). These bird species use large, closed-nests (~40cm and ~100cm length, respectively) built with thorny branches placed on thorny shrubs. The study encompassed nine independent rangelands within the same habitat, but with increasing livestock density, establishing a gradient in grazing intensity. In each rangeland, nest abundance, nest and supporting plant characteristics, vegetation structure and the percentage of browsing were assessed. Plant cover was lower in rangelands with higher livestock impact, and this was associated with lower nest abundance and nest size. Nest abundance of L. aegithaloides was halved, whereas P. gutturalis was decreased 10-fold comparing the extremes of the livestock impact gradient (0.06 vs 1.63 cattle ha−1×years). Nests tended to be smaller and more spherical with increasing livestock impact. The significant and positive association between nest abundance and vegetation structure together with the importance of mating and reproduction for bird lifecycles suggests that the nest abundance of these species could be used as an indicator of habitat degradation. Therefore, furnariid nest abundance could be used as a first step for diagnosing ecosystem health and designing ecologically sustainable management practices in Monte Desert. Changes in vegetation structure (e.g. cover) such as those imposed by livestock may unpredictably affect plant-associated species affecting their reproduction, demography and ecosystem biodiversity.