Feathers about the anus smoky-gray beneath the surface.
Wing about 6.00; fork of tail, .80 deep. ♀ and Juv. Abdominal and crissal feathers always with dusky shafts, and with the concealed portion grayish. Forehead and nape hoary grayish. Hab. Continental North America, south into Northern Mexico … var. subis.
Wing, 5.25; fork of tail considerably less. ♀ and Juv. unknown. Hab. Galapagos … var. concolor.[63]
Wing, 5.80; fork of tail, 1.10 deep. ♀ and Juv. unknown. Hab. Chili … var. furcata.[64]
Feathers about the anus snowy-white beneath the surface.
Wing. 5.50; fork of tail, .90 deep. ♀ and juv. Abdominal and crissal feathers entirely snowy-white,—never with dusky shafts (except ♂ juv. in transition). Forehead dusky grayish-brown; nape steel-blue. Hab. Cuba and Florida Keys … var. cryptoleuca.
b. Females and young with the abdomen dusky grayish-brown.
Wing, 5.50; fork of tail, .80. ♀. Lower parts dusky grayish-brown, the feathers bordered with lighter grayish, producing a squamate appearance. Juv. similar, but feathers of the upper parts bordered with whitish. Hab. Paraguay (Vermejo River) … var. elegans.[65]
B. Adult males with the abdomen and crissum pure white.
a. Lower tail-coverts with the shafts pure white. ♂ (adult) with the throat, jugulum, and sides steel-blue.