夜鳴き鶯

From 夜 (yo, “night”) +‎ 鳴き (naki, stem of 鳴く (naku, “to sing; to chirp”)) +‎ 鶯 (uguisu, “Japanese bush warbler”).

夜(よ)鳴(な)き鶯(うぐいす) or 夜鳴(ヨナ)き鶯(ウグイス) • (yonakiuguisu) 

1. synonym of 小夜鳴き鳥 (sayo nakidori, “common nightingale”)

As with many terms that name organisms, this term is often spelled in katakana, especially in biological contexts (where katakana is customary), as ヨナキウグイス (yonakiuguisu).