"sam" wrote
Every year I have planted onion sets in my modest vegetable plot, and
before they have had time to get established several of them are lifted,
by birds (presumably).The sets are left lying on the ground.Why do birds
do this ? This year,for the first time, I have covered the sets with
fleece, which will remain place until the onions are well established; but
I would still like to know the reason for this strange behaviour.

Just hang some old Cd-roms over the sets and the birds will leave them
alone. They obviously don't like the flashes.
Use a cane pushed in to the ground at an angle and tie string on the top end
like a fishing rod and the Cd on the end of the string so the wind moves it.
Works for us.

--
Regards
Bob
In Runnymede, 17 miles West of London