Pacific Loon
Gavia pacifica
Breeding adults are like a smaller sleeker version of common loon. They measure 58–74 cm (23–29 in) in length, 110–128 cm (43–50 in) in wingspan and weigh 1–2.5 kg (2.2–5.5 lb). They have a grey head, black throat, white underparts and chequered black-and-white mantle. The black throat has purple reflections. Non-breeding plumage is drabber with the chin and foreneck white. Its bill is grey or whitish and dagger-shaped. In all plumages, lack of a white flank patch distinguishes this species from the otherwise very similar black-throated loon. Voice: The Pacific loon most actively calls in the spring and summer and has a wide range of calls. When feeding, the Pacific loon may produce an "ark"-like vocalization, a sharp, short call.
ID text from Wikipedia, CC BY-SA 4.0
Yellow-billed Loon
Gavia adamsii
With a length of 76 to 97 cm (30 to 38 in), a wingspan of 135 to 160 cm (53 to 63 in), and a weight ranging from 4 to 6.4 kg (8.8 to 14.1 lb), the yellow-billed loon is the largest member of the loon (diver) family. The adult is primarily black and white in breeding plumage, with a purple gloss on its head and neck. Appleby, R.H.; Madge, S.C.; Mullarney, Killian (1986). "Identification of divers in immature and winter plumages". British Birds. 79 (8): 365–391.
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: Pacific Loon and Yellow-billed Loon.