When the thrush harvests
When cuckoos mock married men —
A flock of teal fly (6)
A Haiku. The first line refers to Keats’s “What the Thrush Said”, the second line to Shakespeare’s “Spring” and the third line is a double definition.
(Not sure if this qualifies as a cryptic clue, though there was a clue in the form of a Haiku in the Guardian recently)