azure-winged magpie
A bird species (Cyanopica cyanus) found in East Asia. In Japanese, the name is almost always written in katakana.
公園でオナガを見かけました。
I saw an azure-winged magpie in the park.
long-tailed
Prefix used in animal names to indicate a long tail, e.g., オナガドリ (long-tailed fowl). Not freely productive.
オナガドリは尾羽がとても長い鳥です。
The onagadori is a bird with very long tail feathers.
thresher shark; common thresher shark
northern pintail; Anas acuta
long-tailed chicken; long-tailed fowl
The bird name is usually written in katakana. This word is usually written in kana.
Kanji spelling is rare and may be confused with the prefix sense. The source does not list it as a priority form.
From 尾 (o, 'tail') + 長 (naga, 'long'). The bird name derives from its notably long tail.