We searched for nests and studied aspects of the breeding biology of Southern Caracaras (Caracara plancus) in the Patagonian grasslands biome of southern Santa Cruz province, Patagonia, Argentina, at the southern limit of the species' continental distribution. In this open, mostly flat landscape where potential nest substrates are rare and isolated yet conspicuous, caracaras nested in native Magellan barberry shrubs (Berberis microphylla), exotic trees associated with ranch houses and other buildings, on coastal cliffs, and on human-made structures associated with petroleum and gas extraction plants. These extraction activities, which began only in the past three decades in this region have provided new nesting opportunities for this species. Nest characteristics, brood size, and productivity recorded in our study area were similar to what has been previously reported for the Southern Caracara nesting across its broad latitudinal range. In our study area, average productivity in both years combined (2010–2011) was 2.1 fledglings per successful pair (n = 27). The nesting season for this caracara population apparently extends from September through January, phenology that is similar to that reported for caracaras nesting at a similar latitude in Chile and for other raptor species in Santa Cruz province. However, the nesting season seems to be shorter than for caracara populations nesting at northern latitudes in Argentina. In this vast, open landscape, nest substrates provided by human-made structures may be an important determinant of the spatial distribution of Southern Caracara nests.

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