first birdsong of the New Year
Specifically refers to the first warbling or chirping of birds heard at the beginning of the New Year, often associated with the uguisu (Japanese bush warbler). A poetic and seasonal term.
On New Year's morning, I heard the first birdsong of the year from the garden.
I heard the uguisu's first birdsong of the year in the garden.
Standard kanji spelling; used in news and literary contexts.
Compound of 初 (hatsu, 'first') and 音 (ne, 'sound'). The reading ね for 音 is an older native Japanese reading. The term is traditionally associated with the first song of the uguisu in the New Year.