Not sure if I read it somewhere many years ago or have made it up but I've always thought the primary reason for them not being resident in the UK is that our winters are simply not cold enough for them to hibernate properly, so I personally would definitely lean towards captive bred on any springtime sightings.
I have heard the same reason, but I find it hard to reconcile that with the fact that they seem to hibernate in the Oak forests of southern France where the winters are decidedly mild -
just about to post when I saw Guy's post saying the opposite. Added to that, I have to say that I have never seen a Camberwell Beauty (N. antiopa) in Var anytime after the end of the hibernation period. Lafranchis, in his book La Vie des Papillons, says that most antiopa enter into a diapause in mid-July in this region, which would explain the lack of sightings. What happens after that is not clear. He also says that antiopa is highly migratory and uses thermal currents to assist its flight to high altitudes. Filming Var Wild (
https://www.youtube.com/watch?v=WOp6Ea2kcDU) say that antiopa emerges at the end of June in Var and then (immediately?) migrates north. So, do some enter into a diapause and others migrate north?
I have, however, seen a few in the French Alps in July and these have appeared pristine. It may be, based on this empirical evidence, that they travel south to hibernate and that either the hibernators travel north in order to breed, or that they breed in the south and this first generation then heads north immediately. The only evidence I have to suggest the former is the occasional specimen I have seen in the Alps that looks very much as if it had hibernated - one last year at St Dalmas at 1500m which David M will remember. I have also been to sites where several hundred eggs had been found in Var, so clearly egg-laying takes place there, too. It may be that the southern and Alpine populations are entirely separate and have different behaviour. It seems that very little in known about this species.
I certainly concur with Dave that the margins bleach over winter, so any specimen with white borders is almost certainly a hibernator, including the one shown.
I have found that hibernators tend to frequent the same spots each year, with at least some degree of consistency. They tend to remain in these locations for a few weeks. Their flight, even after hibernating, is magnificent, soaring and gliding like no other species.
Roger