Should I stay or should I go? Indirect effects of livestock on bird nest-site selection in arid environments

Introduced livestock may indirectly affect bird species by decreasing vegetation structure and affecting the selection of nesting sites. This is especially true for birds that use shrubs as the raw material for nest construction or for nest placement. Nesting in inadequate supporting structures or the use of inadequate raw material for nest building may increase nest vulnerability (e.g. increasing structure weakness, falling and nest exposure to predation). Accordingly, bird species show a great variation in the selectivity of nesting sites and the raw material they use. Furnariidae family members exhibit an extraordinary diversity in nest placement and structure, which allows them to survive in different arid environments. I report here on a study of nest site selection of two common furnariid species, Leptasthenura aegithaloides and Pseudoseisura gutturalis, across a grazing gradient composed by nine independent paddocks within the same arid habitat. These species use large closed-nests (>40 cm long) built with thorny branches, placed on spiny shrubs. I measured nest abundance and supporting plants characteristics, vegetation structure, browsing intensity and compared the plants selected by the birds with the surrounding vegetation. These bird species used only few plant species for nest building and location. Livestock significantly reduced vegetation cover of the species used to build and place the nests, affecting nest site selection and reducing nest abundance. As livestock density increased, both species selected aggregated plants and the tallest plants for nesting, which may increase nest exposure. Therefore, livestock may indirectly affect nest-site selection of birds ultimately affecting their nesting ecology. This work illustrates how domestic livestock, through decreasing plant cover, may affect native biota with consequences on key species within an ecosystem.