noun
first song/chirp of the year (bird/insect)
Refers to the first vocalization of a particular bird or insect species in a given year, often noted in seasonal observations.
今年のウグイスの初鳴きはまだ聞いていない。
I haven't heard the first song of the Japanese bush warbler this year yet.
気象台がセミの初鳴きを観測した。
The meteorological observatory recorded the first chirp of the cicada.
初音 is a more poetic term for the first song of a bird, especially the bush warbler, often used in classical poetry. 初鳴き is a more general and modern term.
Compound of 初 (hatsu, 'first') and 鳴き (naki, 'cry' or 'song', the continuative form of 鳴く).