I've just heard a very convincing report of a Bittern at Cors Geirch last week courtesy of Eddie. His mate was working a JCB on the edge of the marsh and described seeing a "heron sized bird, many shades of brown with a yellowish bill that was standing in a ditch before walking into the reeds". About as convincing a description as it gets!
Cors Geirch is a great site but access is extremely difficult with just the odd track and footpath crossing it. Even the old bird hide there is completely overgrown. It would be great if CCW improved access - who knows what passes through unnoticed.