From Sounds of Silence, Simon and Garfunkel’s second album, released on January 17, 1966. It had also appeared prior to this on a UK-only release, The Paul Simon Songbook, in August 1965.
The song bears a structural resemblance to a traditional English rhyme, “Cuckoo, cuckoo, what do you do?”, a phenology of the Common Cuckoo from April to September:
Cuckoo, Cuckoo, what do you do?
“In April I open my bill;
In May I sing night and day;
In June I change my tune
In July far far I fly;
In August away I must.”
This choral version of the rhyme was featured on the soundtrack to Wes Anderson’s 2012 film, Moonrise Kingdom: