Pallas's rosefinch
A species of rosefinch (Carpodacus roseus) found in East Asia. In Japanese, the name is almost always written in katakana.
In winter, Pallas's rosefinches migrate to Japan.
Katakana spelling is standard for this bird name; the kanji form 大猿子 is rare.
Kanji form is rarely used; the katakana spelling is strongly preferred.
The name オオマシコ is a compound of 大 (large) and マシコ (rosefinch). The exact origin of マシコ is uncertain, but it is a traditional Japanese name for rosefinches.