Visitors to the seaside this summer might like to look out for two uncommon species of gull which, if they are lucky, they could see without moving from the beach. These are the yellow-legged gull and the Mediterranean gull.

Yellow-legged gulls, pictured, are very like the herring gulls that are so common along the coast. In the past, in fact, they were considered to be merely a subspecies of the herring gull, and they have only just been recognised as a separate species. You will find them mentioned only in the latest bird guides.

They stand out because of their rich yellow legs. Herring gulls’ legs are normally pink. The yellow-legged gull has also got a darker grey back than the herring gull, though it is not as dark as the lesser black-backed gull, and it has more black on the wing-tips.

It used to be mainly a Mediterranean species. On the airport boat that takes you across the water to Venice, you see them standing all the way on the wooden poles that mark out the route. Recently, they have started nesting on cliff ledges and roofs in seaside towns farther north.

From late July to September there is usually quite an influx of wandering yellow-legged gulls into Britain, and there have been one or two attempts at breeding here. One bird hybridised here with a lesser black-backed gull, to which it may be more closely related than to the herring gull, in spite of appearances.

Indeed, if you see what looks like a herring gull consorting with some lesser black-backs over the sea, it is worth giving it a good scrutiny, since it may well prove to be a yellow-legged.

The Mediterranean gull is like that other common British gull, the black-headed gull. It too has a black head in summer. However, the black-headed gull’s hood is more like a face-mask, not extending to the back of the neck, whereas the Mediterranean gull’s hood completely covers the head, including the back of the neck.

Mediterranean gulls are also slightly bigger, and look very white, without the black-headed’s black wing-tips. They have a red beak and red legs like the black-headed gull, but the beak is thicker and the legs are longer.

Mediterranean gulls have gone farther than yellow-legged gulls and now breed here, with about 100 pairs nesting each year, mainly on the South Coast, but also in Scotland and Ireland. They often nest in black-headed gull colonies. Like the yellow-legged gulls, they have added a new interest to gull-watching in this country.

derwent.may@thetimes.co.uk