Golden-crowned Kinglet
Regulus satrapa
Adults are olive-gray on the upperparts with white underparts, thin bills and short tails. They have white wing bars, a black stripe through the eyes and a yellow crown surrounded by black. The adult male has an orange patch in the middle of the yellow crown. The juvenile is similar to the adult, but with a browner back and without the yellow crown. This is one of the smallest passerines in North America. Its length, at 8 to 11 cm (3.1 to 4.3 in), is probably the shortest of any American passerine. Its weight, averaging 6.1 g (0.22 oz) for females and 6.3 g (0.
ID text from Wikipedia, CC BY-SA 4.0

Ruby-crowned Kinglet
Corthylio calendula
The ruby-crowned kinglet is a very small bird, being 9 to 11 cm (3.5 to 4.3 in) long, having a wingspan of 16 to 18 cm (6.3 to 7.1 in), and weighing 5 to 10 g (0.2 to 0.4 oz). It has gray-green upperparts and olive-buff underparts. It has two white wingbars and a broken white eye ring. The wingbar on the greater secondary coverts (closer to the wing-tip) is wider, and is next to a dark band. The kinglet has a relatively plain face and head, although the male has a scarlet-red crown patch, which is usually concealed by the surrounding feathers. Voice: The ruby-crowned kinglet's vocalizations are remarkably loud and complex for its size. Its song can be divided into three main parts: a series of high pitched notes (zee-zee-zee or tee-tee-tee), two to five low trills (turr or tu), and a repeated three note "galloping" phrase (tee-da-leet, tee-da-leet).
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: Golden-crowned Kinglet and Ruby-crowned Kinglet.