This video from Britain says about itself:
BTO Bird ID – Small black-headed gulls
17 July 2014
A hooded gull in summer is likely to be the ubiquitous Black-headed Gull, but there are a couple of other species that sport the same summer finery. Would you be able to pick out a Little or Mediterranean Gull from the crowd?
From Discover Wildlife in Britain:
6 black-headed gull facts you need to know
Discover 6 fascinating facts about the BTO December Garden Bird of the Month.
14th December 2015
By Clare Simm
1 Population boom and bust
During the early 19th century, black-headed gulls were quite rare. However, a dramatic population increase throughout the 20th century saw their breeding population rise to over 100,000 pairs. While their breeding population is still growing, their winter numbers have fallen by over 30 per cent in the last 25 years and they are an Amber Listed bird of conservation concern.
2 Urban gull
Black-headed gulls were rare inland over 100 years ago. However, they now use inland sites for breeding, roosting and foraging and are the gull species most commonly seen in urban and suburban gardens. Inland breeding colonies can range from fewer than 10 pairs to over 20,000 and are found throughout the country, including in central London.
3 Wide diet
Their diet consists of a variety of different foods, including insects, plant material, earthworms and human leftovers. Their catholic diet means that they regularly visit gardens in search of kitchen scraps. They are quite feisty birds and groups will often squabble over available food, especially when there are few feeding opportunities.
4 Garden birds
Gardens seem to become more important for black-headed gulls during the coldest winter months of January and February because food is harder to find. However, BTO Garden BirdWatch results show that they are increasingly visiting throughout the year. Outside of winter, individuals visiting gardens are often likely to be immature, non-breeding birds from local colonies.
5 Winter migrants
While most of our breeding population are resident birds, it is estimated that more than two-thirds of black-headed gulls wintering in the UK have come from mainland Europe. This migration happens from late summer with earlier arrivals thought to be young birds from Western Europe. Birds often seem to be site-faithful, returning to the same place year after year.
6 Brown-headed gulls
Despite their name, black-headed gulls don’t have black heads. During the breeding season their heads are dark chocolate brown, and in the winter they are white with dark brown smudges on the side. They have a dark red bill and legs. Juveniles have brown shoulders and wing feathers, gradually gaining the adults’ grey/silver coloured wings over a couple of years.
Gulls are very familiar birds with different species found in a range of habitats worldwide, but how much do you really know about them? These facts about gulls can surprise even experienced birders: here.
This study presents the first data on a breeding colony of the Black-headed Gull on islets of the Al Massira reservoir in central west Morocco from 2002 to 2008. Laying phenology, nesting site selection, clutch size, egg size and breeding success were investigated. These data provide new information at the southwestern limit of the species’ breeding area (32° N): here.