Black-headed Brushfinch
Arremon atricapillus
The black-headed brushfinch is about 19 cm (7.5 in) long and weighs about 49.5 g (1.7 oz). The sexes have the same plumage. Adults have an almost entirely black head with a white throat. Their upperparts, wings, and tail are olive-green. The white of the throat continues through the breast and belly. The sides of their breast are gray and their flanks and vent are grayish olive. They have a dark chestnut-brown iris, a black bill, and blackish legs and feet. Juveniles have a greenish olive head and upperparts, dull brown wings and tail, and tawny underparts. Subspecies A. a. Voice: The black-headed brushfinch's song is "a high-pitched series of rambling notes which proceed without breaks" and its call is "a sharp note".
ID text from Wikipedia, CC BY-SA 4.0

Sierra Nevada Brushfinch
Arremon basilicus
The Sierra Nevada brushfinch is about 19 cm (7.5 in) long. The sexes have the same plumage. Adults have a black crown with a gray stripe in the middle, a gray supercilium that extends to the nape and continues behind the ear coverts. The rest of their face is black. Their upperparts, wings, and tail are olive-green. Their throat is white with a narrow black band below it. The center of their breast and belly is white and their sides, flanks, and vent are brownish olive. They have a dark chestnut-brown iris, a black bill, and blackish legs and feet. Voice: The Sierra Nevada brushfinch's song is "a high-pitched sibilant series of notes...with very fast delivery and almost nervous sound, this due also to inclusion of some quavering high-pitched whistles". Its call is "a sharp note".
ID text from Wikipedia, CC BY-SA 4.0
Where you might meet both
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Play today's Daily BirdPhotos and recordings are credited to their authors under the licence shown. Full profiles: Black-headed Brushfinch and Sierra Nevada Brushfinch.