A Javan endemic, this rare and enigmatic swiftlet breeds in the craters of a handful of active volcanoes. Forages over the craters and surrounding montane forest. Dark brown above and paler below, with a forked tail and paleish rump. Other dark swiftlets are unlikely up in the high altitudes where Volcano Swiftlet occurs, and average more square-tailed, though this can be difficult to judge accurately. Gives high-pitched screams and clicks.