Typical “white-bellied” swiftlet, endemic to Java, Sumatra, and smaller adjacent islands. Dark above, with a gray-brown breast and white belly. Note squared-off tail and green gloss on the back (only visible in good lighting). Rapid flight is erratic and bat-like. Can generally be seen over a range of habitats from lowlands up into highlands, but restricted to highlands in Sumatra. Extremely similar in appearance to Plume-toed Swiftlet, which has a bluer gloss (though lighting can make this tricky) and feathered hind toes (typically only visible in the hand). Gives a dry, scraping chittering, particularly at roosts.