These dark patagial marks on the underwing are only found on the red-tailed hawk.
From the sltrib.com
In flight a yellow wing-bar contrasts clearly with the red underwing coverts.
From the en.wikipedia.org
The underwing is warm yellow, the bill is yellowish and the legs and feet are pink.
From the en.wikipedia.org
Re-engined as per the T-28B and C, and fitted with six underwing hardpoints.
From the en.wikipedia.org
When circling overhead, the white underwing of the bird becomes conspicuous.
From the en.wikipedia.org
The underwing is predominantly white with broad, irregular, black margins.
From the en.wikipedia.org
These planes become rarer as almost all newly built airliners have underwing nacelles.
From the en.wikipedia.org
The underwing is grayish with dark tips to the outer primary feathers.
From the en.wikipedia.org
Yellow underwing feathers are usually associated with eastern Kansas.
From the kansas.com
More examples
Moth having dull forewings and brightly colored hind wings
Catocala is a genus of noctuid moths commonly known as Underwings. (A few closely related genera are sometimes called Underwings as well, but usually the term is synonymous with this genus.) Most species have brightly coloured underwings, orange, red, or white. ...
(Underwings) The underside of a butterfly's wings, as seen when the animal is at rest with wings closed. Not to be confused with the hindwings, the second (rear) pair.
A wing, usually of a whole hackle, hackle tip or fibres, that is tied in under the body.