Calidris alba is monotypic, and has a very large range. It winters in zones of moderate to tropical climate, in several continents, including South America.
Figure 1. The non-breeding Sanderling has white underparts and mostly pale-gray upperparts, like the bird on the photo.To top of page
Figure 2. Small group of Sanderlings Calidris alba on the beach of Acaraú, in August 2009. The Sanderling lays in its northern breeding grounds in June and July (Gils, van J. and P. Wiersma 1996). Based on this, I would not expect any Sanderlings back in Brazil as soon as August (date of this photo), and entirely in non-breeding plumage. But is has also been reported that some birds remain in the South the entire year (Gils, van J. and P. Wiersma 1996), and this could be the case here.
I checked the wikiaves photo registers (downloaded 1/3/2011) for Calidris alba, to see how common August registers in Brazil are. There were 183 photos of Sanderlings uploaded. After eliminating a few cases because they were not from Brazil, or doubles, I obtained the following statistic of registers per month:
The statistic confirms that part of the Calidris alba population stays in Brazil all year long. The only unexpected result is the dip in March (Carneval?).