I've always (well for the last few years since I moved up the valleys) thought that all the gulls around this area roosted on Pontstic' res, except their rare shift to Llwyn Onn. Walking home from the station this evening I noticed a group of large gulls flying down the Taf, from the Merthyr direction. In a 10 minute period I counted over 200 heading down the valley, towards Cardiff. I guess they were heading to roost in Cardiff Bay area as I can't think of any large water body that way before you hit the Bay. I've not noticed any significant movement og gulls down the valley previously, though I have noted gulls flying up the valley early in the morning., so it shouldn't have been much of a surprise. This number of gulls would constitute some 10% of the Pontstic' roost (Mike, correct me if I've got my maths wrong). A portion of the Merthyr feeding gulls roosting down the Bay would go some way to explain the occasional Great Black Backed, Yellow-legged, Iceland and Glaucous turning up in the area.