Merín Lagoon, Uruguay – a new important non-breeding site for the Buff-breasted Sandpiper Calidris subruficollis

The Buff-breasted Sandpiper Calidris subruficollis is a long-distance migratory shorebird of global conservation concern. During the non-breeding season, the species concentrates on grasslands in southern South America. High densities have been reported at six sites, but more sites with high concentrations are suspected to exist. Here, we estimated Buff-breasted Sandpiper abundance within a grassland sector near the Merín Lagoon, Uruguay. To estimate abundance within this grassland sector, we randomly selected transect lines in areas where concentrations of Buff-breasted Sandpipers had been seen previously. We estimated abundance in two austral summers (Jan and Dec 2021). In the first season, using the mean density of 10.1 birds/ha recorded in an area of 1,650 ha, we estimated an abundance of 16,665 individuals (95% CI = 8,019–25,410). In the second season we estimated a density of 8.7 birds/ha in an area of 3,829 ha, resulting in an abundance estimate of 33,427 (95% CI = 10,644–56,286). These numbers represent between 29.8 and 59.7% (using mean value) of the global population in ca. 4,000 ha. However, such large numbers may be inflated as large groups of birds were present in the study area during both years of our study and we focused our sampling in areas known to contain Buff-breasted Sandpiper. Therefore, these estimates cannot be used to extrapolate to areas outside of our original sampling frame. Regardless, the regular occurrence and large numbers (even based on just the direct counts) of Buff-breasted Sandpiper suggest that Merín Lagoon is an important wintering site for them. Coastal grasslands appear to be widespread around the lagoon (ca. 250,000 ha), although more studies are needed to determine the extent of suitable habitat (short grass) and its use by Buff-breasted Sandpipers. The large number of birds that repeatedly use this area indicates it is essential to continue managing this area for livestock production, so as to maintain the short grass preferred by Buff-breasted Sandpipers.