Vocalizations of Black Swift rarely are heard except at nest sites and even then are difficult to hear because of noise of falling water typically present at nest sites. Rathbun (1925) reported chatter-like notes given during flight near the close of the day and surmised that during breeding vocalizations were given at the time when one bird dashed at another, especially when a pair flew in close company. At one breeding site (Andrews Glacier Cave in Rocky Mountain National Park, Colorado, with only small amount of falling water), high-quality recordings have been obtained by Pieplow and Spencer and can be accessed at the xeno-canto website (xeno-canto 2012).
It has been hypothesized that Black Swifts may have echolocation capabilities similar to other cave-dwelling bird species since they often vocalize while returning to breeding sites in complete darkness and some breeding sites are in caves. A bat detector used in a cave with a large colony in which audible vocalizations were heard detected no ultrasonic vocalizations (C. Gunn personal observations). More study is needed.