Abstract
Changes in the structure of grasslands have been responsible for the decline of several avian species due to the reduction in the quality of available habitat. In the Flooding Pampas (Argentina), espartillares of Spartina densiflora are marginally productive areas for cattle rearing and show great variation in the intensity of their use by ranchers as grazing areas. In this work we compare the responses in abundance and richness of avifauna in espartillares with different stocking rates in the Samborombón Bay area. Our treatments were: 1) plots with low stocking rate (0.4 cows/ha), and 2) plots with high stocking rate (0.8 cows/ha). Our study covered three periods of the birds’ breeding cycle (early, late, post-reproduction) over two years (2011/2012, 2012/2013). The sites with high livestock rate had greater vegetation coverage in the stratum lower than 11cm and lower height with respect to the sites with low livestock loads. Species richness and total abundance of birds were 23% and 29.5% lower, respectively, in grasslands with high livestock rates. Also, species richness and abundance of tall grassland species were 60% and 61% lower, respectively, in grasslands with high livestock rates. High stocking grazing substantially affects the abundances of tall grass specialist species such as the Bay-capped Wren-spinetail (Spartonoica maluroides) and the Sedge Wren (Cistothorus platensis). We encourage to preserve espartillares with high structure (> 70 cm) and dense vegetation, keeping some paddocks or paddock areas in rest/exclusion, instead of a general adjustment of the animal stocking rates for the entire establishment.
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