You see them in all seaside towns
Late summer, say, around the time
The schools go back. They congregate
Like swallows do on lines and wires
To rest before that long hard journey
From these shores, or like late autumn
Butterflies that find a warm
And sheltered spot late in the day
Before the sun goes down.

Basking there in the still warm air
It seems as if these too prepare
This afternoon for their long journey
To another shore. They softly twitter,
Snooze, recline in peaceful rows
On hired deckchairs in the sun
And like the swallows, in their bones
They know that winter soon will come.

Pete Crowther

http://www.poemhunter.com/poem/late-summer-migrants/