Rothschild's Swift (Cypseloides rothschildi) is among the least known South American swifts. Here we clarify its distribution and seasonality, and provide detailed natural history data and breeding information. We compiled 197 records of Rothschild's Swifts (museum specimens, citizen science initiatives, literature, and field observations) from Argentina and Bolivia; most from the breeding season (Oct–Mar, 177 records; 44 documented), a few thought to be on migration (Apr and Sep, 15 records; 3 documented), and fewer during the nonbreeding period (May–Aug, 5 records; 1 documented) with no records from July/August. Rothschild's Swifts are migratory, but the wintering quarters remain unknown. The distribution during the breeding season is broadly overlapping with the Austral Yungas of Argentina and Bolivia, with sparse records in Andean and extra-Andean ranges with forested and non-forested waterfalls. Our breeding distribution model indicated high presence probabilities in the Austral Yungas of Bolivia and Argentina. The breeding season during the austral spring and summer (late Oct/mid-Nov to mid-Mar/early Apr in northwest Argentina) began roughly with the early rains as in other Neotropical swifts. Our data from 8 breeding sites and from 8 nests that we studied in northwest Argentina regarding nest placement (near waterfalls), nest features (moss or moss and mud cups), eggs (single and white), and on the protracted development of Rothschild's Swift nestlings (∼55–60 d) and the sequence of plumage acquisition and behavior were coincidental with what is known from other Cypseloides. We provide behavioral information from a temporarily captive individual, which provided the first sound recordings of nestling/fledgling vocalizations of Rothschild's Swift—presumably the first available for any Cypseloides. It is unclear whether these vocalizations, recorded in captivity, represent developmental precursors of adult sounds or begging calls.

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