Vegetation structure and selection of reproductive habitats by Pampas grassland birds

Abstract

The increasing transformation of natural grasslands into agricultural fields affects grassland birds with particular severity, as their breeding success depends strictly on these habitats. This study focuses on bird species that nest in the Ernesto Tornquist Provincial Park in the southwest of Buenos Aires province (Argentina). We conducted intensive nest surveys during three reproductive seasons, recording their site characteristics and evaluating nesting preferences of needlegrass grasslands (dominated by Stipa and Piptochaetium species, “flechillares”) and tussock grasslands (dominated by Paspalum quadrifarium and Cortaderia selloana). We found 214 nests, belonging to 12 species, built within grass tussocks or directly on the ground. Paspalum grasslands represent 7.75% of the surveyed area but contained 76.65% of the nests, showing a significant preference for this type of habitat. Low nest abundance of obligate grassland species, typically associated to “flechillares”, e.g. Grassland Sparrow (Ammodramus humeralis), Grass Wren (Cistothorus platensis) and Correndera Pipit (Anthus correndera), and the complete absence of Red-winged Tinamou (Rhynchotus rufescens) nests, was particularly worrying. Our results may reflect the particular vulnerability of species nesting in “flechillares”, a habitat the structure of which is more deeply affected by big herbivores.