Just after the end of the Second World War I started a collection of British wild birds. A large aviary to contain them, complete with a shelter and plenty of growing vegetation made for a very satisfying hobby. All birds had to be closed ringed to ensure that they had been hatched and reared in captivity. I had concentrated on finches with Norwich canaries to obtain some sweet singing hybrids and initial results were patchy but mildly successful.
One day a stranger came to the door and asked if I had a cock goldfinch for sale. We went up to he aviary, selected a bird and whilst examining the rest of the bunch the purchaser noticed an unusual looking bird which I identified as a bullfinch/canary hybrid, the only one I had ever bred before or since.
Great discussion now as to the value of the bird, but all offers were rejected out of hand. On my daily visit to the aviary I could not see the hybrid, and could not discover how the bird could have escaped. The mystery was solved some 23 months later when talking to a friend at the local bird show, he asked me if I had had a visit from Tom the well known (but not to me) bird trapper of an adjoining parish. On relating his visit and my loss he replied "Tom had that one the same night I'll bet, he is notorious for that sort of thing, he will walk ten miles in a night across country for that sort of bird and what's more he wanted that goldfinch to use as a call bird in one of his trap cages". Lesson learned, but dearly.