It's almost a cliché to state that gulls "are not to everyone's taste". Indeed, that may well be the case – habits, habitat and oft-bewildering identification challenges tend to put a lot of people off. That said, increased airtime – largely thanks to dedicated internet sites such as the wonderful gull-research.org – has contributed to an ever-growing band of birders dedicating their time to searching the various rubbish dumps, estuaries, ports, harbours and beaches at which gulls tend to gather.
At this time of year, Yellow-legged Gulls are at their most numerous across Britain & Ireland as post-breeding dispersal from breeding grounds further south and east brings birds to our isles. Good numbers can generally be found across much the South East and parts of the Midlands, with gulls lingering to moult before their numbers gradually drop off again throughout the autumn (though plenty do stay for the winter).
The River Thames estuary is really the hub of Yellow-legged Gull activity in Britain, and mid-July to mid-September generally witnesses the highest counts reported as birds congregate to moult in the area – for example, 145 were at Rainham on 9th September 2012 and, just yesterday (6th August 2013), 142 were counted on the Kent side of the Thames between Greenhithe and Dartford.
The Rainham area is a great place to get to grips with Yellow-legged Gulls, with the late summer period also offering a fine opportunity to compare juveniles with their Herring and Lesser Black-backed counterparts. Though birds are often feeding out of view on the dump itself (to which there is strictly no access), birds can be watched from the adjacent riverside footpath as they commute to the river to bathe and loaf. Though birds can often be swimming mid-channel at high tide (and thus may be distant), low tide sees them loafing on the exposed foreshore where they give excellent views from the footpath. Parking is available in the riverside car park off Coldharbour Lane (grid reference TQ516801). From here, walk southeast along the river for up to a mile to view any concentrations of gulls along the river.
In a three-hour visit to Rainham yesterday morning, I had at least 35 Yellow-legged Gulls of all ages, with juveniles and adults being the most common age class. Take a look at the juvenile below, and see if you can work out what makes it a Yellow-legged:
It is worth noting that this individual has an atypical bill colouration - Yellow-legged Gulls almost exclusively show dark bills well in to their first winter (and the following summer) - but, apart from that, exhibits classic plumage. Note the overall paleness to the underside and head, dark 'shadow' around the eye, covert pattern, largely brown tertials with limited notching at the tips (some have no notching) and, crucially, scapular pattern. The bird has already begun to replace a number of its juvenile scapulars with second-generation feathers (those with the anchor-shaped markings on) - this early moult is almost unheard of in Herring and Lesser Black-backed Gulls, given that they fledge up to several weeks later than Yellow-legged and generally look as though they are 'fresh from the nest' in early August. Note also the bird's slender, long-winged structure and long legs.
The same bird is portrayed above in flight, illustrating the characteristic tail pattern of the species - a largely white rump and upper tail (with limited brown flecking) and a crisply-defined and narrow black tail band that tapers towards the outer tail feathers.