Hi Hazel
I've no personal experience of this but it sounds a plausible scenario. Certainly Black-headed Gulls can be quite clingy often pestering their parents for food when they are perfectly capable of fending for themselves. I guess the juvenile/parent bond exists for a while after fledging even if they are nominally independent.
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Tony
My Flickr Photostream
Sounds like the juveniles were food begging - and the parents would have chased off any chicks they hadn't raised so I think you're correct in saying they're a family. I've seen at least one situation where an immature herring gull (almost a year old) was chasing an adult for food, and the adult wasn't at all hostile - in fact it was scuttling away with a look on its face that suggested it wished it could abruptly be somewhere else! The family bond clearly lasts a while with these birds.
Our herring gulls are red listed birds. Think about that the next time you hear some flaming idiot calling for a cull of them.
Juvenile herring gulls often hang around with their parents for as long as possible after fledging. In my local colony last year, all migrated in mid-September, up until which point the juveniles were still mostly with their parents and obtaining food from them. The adults returned in mid-November minus their offspring! In town, where the gulls didn't migrate, I noticed that one “chick” stayed with his (I’m guessing he because he was massive, and males are generally larger than females) parents for almost a full year, until the next breeding season started!
The clucking sound you refer to is probably “choking”, which is a territorial call to defend their nest area.