Med Gulls moving inland during the winter in Spain were monitored much as Harry suggests and it was found that they were attracted to olive groves where they feasted on the dropped fruit. However I hesitate to put forward this theory as I haven't noticed any olive trees east of Tan Y Bwlch!
'Daily rhythms involve birds moving between offshore feeding areas during the day (where they
largely consume fishing discards) to inland olive crops and bathing and drinking sites (Riudecanyes reservoir) in the afternoon, and finally to coastal roost sites at dusk (Cambrils). '
All goes to show what successful birds they are being opportunistic feeders so there's something inland they are after!
