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Nest-site selection by male Greater Rheas

Abstract Greater Rheas (Rhea americana) are ground-nesting birds that have high rates of nest desertion commonly associated with egg predation. We studied whether male Greater Rheas selected concealed sites to decrease detectability of their nests. We analyzed the spatial distribution of nests and compared the microhabitat characteristics of nest sites vs. sites selected at random, and sites of successful nests vs. sites of deserted nests. We also used experimental nests (nests without male attention) to assess whether egg losses were associated with the microhabitat characteristics of the nest site. The distribution of nest sites differed significantly from a random pattern, and nest sites had a higher percentage of shrub cover, a lower percentage of grass cover, and a higher concealment (low overall visibility) than sites selected at random. However, none of the microhabitat characteristics that we analyzed were associated with nest failure or the rate of egg loss. Experimental nests that were more visible tended to suffer higher and faster egg predation than less visible ones. Our results indicate that Greater Rheas selected concealed sites for nesting, but they did not get any apparent benefit for selecting these sites. We propose that habitat alteration and the type of predation that this species suffers at present may have reduced the benefits of selecting concealed sites for nesting.