Common Characters. Above brown, varying from nearly gray to bright ferruginous, in some species this color interrupted by a more or less distinct whitish nuchal collar, with an adjacent blackish spot (sometimes concealed) on each side of the neck. Tail with narrow bands. Beneath white, the sides striped with brown or blackish. Throat and jugulum white, with a dusky collar between. Crown speckled or streaked with lighter; wings more or less spotted with the same.
A. Markings on the crown circular, or dot-like.
1. G. passerinum. Tail with six to eight narrow white bands. Upper parts varying from brownish-gray to chocolate-brown. Ground-color of the lower parts pure white.
Tail, and stripes on sides, not darker than the back; tail-bands six, and continuous; toes rather thickly feathered. Hab. Europe … var. passerinum.[32]
Tail, and stripes on sides, much darker than the back; tail-bands 7 (♂)–8 (♀), not continuous; toes only scantily haired. Wing, 3.50–4.00; tail, 2.50–2.80; culmen, .43–.48; tarsus, .60; middle toe, .55. Hab. Western Province of North America. Table-lands of Mexico … var. californicum.
B. Markings on the crown longitudinal and linear.
2. G. infuscatum. Tail dark brown, crossed by six to seven non-continuous bands of white, narrower than the dark ones. Above varying from grayish-brown to reddish-umber and sepia. Beneath white, the stripes on the sides grayish-brown or dark brown, like the back.
Above dark sepia, or blackish-brown. Tail brownish-black or deep black. Wing, 3.70–3.90; tail, 2.50–2.90; culmen, .45; tarsus, .65–.80; middle toe, .65–.70. Hab. Eastern South America … var. infuscatum.[33]
Above grayish, or reddish-umber. Tail clear dark brown, or grayish-umber.