The Biscutate Swift is distributed in eastern Brazil from Piauí to Rio Grande do Sul and into adjacent areas of north-eastern Argentina. It appears to be partly or wholly migratory but its movement are not fully understood according to HBW  which says that it is possibly a transequatorial migrant.

Consulting Wikiaves on 8th September 2009, there are 4 photos for this species from the states of Minas Gerais (August and December), Rio de Janeiro (October) and Parana (January) to set beside these photos from Bahia in October.

As we approached Lençois we noticed some swifts flying low over the road and on reaching Lençois we saw an enormous flock of several thousands spiralling high up in the sky (photo 2).  

Guy Kirwan, in an article in Neotropical Birding, Number 2, Pages 24 to 26 gives features that allow the identification of Biscutate from White-collared Swifts. The easiest feature with good views as in photo 1 is the broken white collar of the Biscutate but he also mentions that the white on the neck of the Biscutate is overall distinctly broader than on White-collared and that Biscutate shows a paler forehead, chin and lores.

There are recordings on xeno-canto, a distribution map from NatureServe and additional information available via Avibase.