Five barn owl boxes which are part of a Suffolk community project have been stolen or vandalised, with the animals taken to "spend their lives in cages".
The boxes were erected in an attempt to halt a decline in barn owl numbers.
They are made by a group of disabled people and Hollesley Bay prisoners, and monitored by volunteers.
Kathy Piotrowski, of the Suffolk Community Barn Owl Project, said it was sad that a "few mindless people" were undoing people's hard work.
About 1,700 boxes have been put up around the county and they have been credited with helping to turn around the birds' fortunes locally.