I have just witnessed Gull behaviour i haven’t seen before.A flock of 20 or so Black Headed Gulls appeared to be flying around and hovering over lake-side trees laden with berries.I was 200yds. away with just bins.They seemed to be actually taking berries,but couldn’t be certain.On reaching my car i got my scope out and eating berries was exactly what they were doing.Has anyone else seen or heard of this kind of behaviour?
Glamorgan Bird Club 
I have never see it but BWP has the following entry for Black headed Gull: Plant material (especially summer and autumn) includes fruits and seeds, e.g. cherries, olives Olea, figs Ficus, haws Crataegus, crowberries Empetrum nigrum, whortleberries Vaccinium uliginosum, acorns Quercus, beech-nuts Fagus, berries of whitebeam Sorbus aria; also cereal grain taken from stubble in autumn, and in spring from recently sown fields; weed seeds, including Polygonum and Stellaria; vegetative parts, e.g. leaves of clover Trifolium.
I saw this a couple of winters go at Cosmeston when B-h Gulls were plucking berries in flight, from Hawthorn alongside the central path.