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.