black-backed wagtail
A subspecies of the white wagtail (Motacilla alba lugens), common in Japan. The name is usually written in katakana.
I saw a black-backed wagtail in the park.
Standard katakana spelling for this bird name.
Kanji spelling is rare; the word is usually written in kana.
From 白 (haku, 'white') + 鶺鴒 (sekirei, 'wagtail'). The exact derivation is uncertain, but the name refers to the bird's coloration.