Worse, the number of pheasants alleged to be released in the UK each year would require a single pen larger than the entire land surface of Earth.


like it
200 metres circumference minimum as a starting point for 200 to 400 birds.
A smaller pen with no cover or roosting will fail.
The most important thing is to have plenty of cover, grass ,bushes, medium trees ,taller trees, sunny spots, dry ground.
The birds need to be happy, secure, able to hide in cover, able to sun themselves , dust, scratch ,peck at green stuff, drink fresh clean water, eat the feed without being hawked.
Get all these things right and you can have a much smaller pen than the theory suggests.
Its essential when you stand one side you cannot see straight through to the other.
If you can, any fox or dog running round the pen will spook them prematurely.
Check that the re-entry holes
actually work
one way , the right way
You need to keep the birds in the release pen long enough that they recognise it as a safe home.
Also establish feeding dusting stations around the pen.
The more brambles etc they can peck at means they wont turn cannibal. Give them a lettuce a day.
They will fly out and wander but then should return in the evening .