	Unlike some swift species, which mate in flight, chimney swifts mate while clinging to a vertical surface near their nest. They copulate daily, until the clutch is complete. The female typically lays , though clutch sizes range from . The eggs, which are long and elliptical in shape, are moderately glossy, smooth and white, and measure . Each weighs nearly of the female's body weight. Incubated by both parents, the eggs hatch after . Baby chimney swifts are altricial—naked, blind and helpless when they hatch. Fledglings leave the nest after a month.