At this time of year groups of gulls congregating on frozen lakes and ponds are good for both photography and the sharpening of those identification skills. Gulls as a group can be very tricky with differing age and seasonal plumage, and are therefore something of an acquired skill that needs to be worked at to build confidence. Only recently I agonised over a large gull that had come in to roost on Ponthir Reservoir. Was it a ring billed or just a common or garden herring gull? The latter prevailed but the varying amount of dark markings on bill had me going for a while.
The common gulls depicted in the above image illustrate how plumages differ depending on age. My assessment of these gulls would be:
Left hand bird: Adult winter - note crisp plumage with slight streaking of head and slight bill band.
Middle bird: 2nd winter - heavier streaking to head and breast with thicker bill band.
Right hand bird: 1st winter - blend of immature and adult plumage with well defined dark tip to bill.