Lesser Goldfinch
Spinus psaltria
This species is not only the smallest North American Spinus finch, it may be the smallest true finch in the world. Some sources list more subtropical Spinus species as slightly smaller on average, including the Andean siskin (Spinus spinescens). This species ranges from 9 to 12 cm (3.5 to 4.7 in) in length and can weigh from 8 to 11.5 g (0.28 to 0.41 oz). Among standard measurements, the wing chord is 5.5 to 7 cm (2.2 to 2.8 in), the tail is 3.9 to 4.7 cm (1.5 to 1.9 in), the bill is 0.9 to 1.1 cm (0.35 to 0.43 in) and the tarsus is 1.1 to 1.2 cm (0.43 to 0.47 in).
ID text from Wikipedia, CC BY-SA 4.0
Pine Siskin
Spinus pinus
These birds are fairly small, being around the same size as the widespread American goldfinch. In both sexes, total length can range from 11–14 cm (4.3–5.5 in), with a wingspan of 18–22 cm (7.1–8.7 in) and a weight of 12–18 g (0.42–0.63 oz). Adults are brown on the upperparts and pale on the underparts, with heavy streaking throughout. They have short, forked tails. Their bills are conical like most finches but are more elongated and slender than those of other co-occurring finches.
ID text from Wikipedia, CC BY-SA 4.0
Where you might meet both
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Play BeakBrainPhotos and recordings are credited to their authors under the licence shown. Full profiles: Lesser Goldfinch and Pine Siskin.