Waterbird Wednesday week 5 - Common Gull
The Common Gull (Larus canus) is, despite it's name, not the most common gull in the UK. They are, however, commonly seen in the winter, especially at the coast but also inland. They are slightly larger than Black-headed Gulls, with a wingspan of 100-115cm. The wintering population is estimated at around 710'000 birds, and there is a much smaller breeding population of an estimated 49'000 pairs. The breeding population in much more concentrated in the north. They normally nest inland, with the nest itself on the ground - the nest varies from being a small scrape to a substantial platform of grass and other vegetation.
Identification
Overall, a Common Gull is larger than Black-headed and much smaller than Herring. They have narrow bills, and, in flight, appear much slimmer and more elegant than species such as Herring Gull. The iris is dark at all ages. Common Gulls can be seen in 7 different plumages.
Juvenile
A juvenile Common Gull looks brownish overall, with a brownish head and breast, and brown wing-coverts. Pale tips to the wing-coverts give them a scaly effect. The flanks are faintly barred brown, and the tail has a thick black terminal band. The primaries and primary coverts are black, but there is a pale window in the primaries. The under wing is marked brown, and there are brown markings on the uppertail coverts. The secondaries are dark, which gives the effect of a dark trailing edge to the wing. The bill is pink at the base, with a large black tip. The legs are pink.
1st-winter
In 1st-winter plumage, a bird will still have wing and tail feathers retained from juvenile plumage. They have moulted the head and bod feathers, as well as the scapulars. The bird's back is now plain grey. The bird has lost it's brown breast, and now has brown streaking on the head. The nape is still coarsely marked, but the breast only has some brown markings that continue down the flanks. The pink and black on the bill is now much neater, with an obvious black tip. The legs are still pink.
1st-summer
1st-summer plumage is very similar to 1st-winter, however the head feathers are moulted and lots of the head markings are lost - however there is still brown on the neck.
2nd-winter
When a Common Gull enters 2nd-winter plumage, it finally moults it's juvenile tail and wing feathers. The tail is completely white, and the inner part of the wing is grey apart from a white trailing edge to the wing. However, there is a lot of black on the primaries, primary coverts and alula, and a small white "mirror" on the outer primaries. There is lots of brown markings on the head, neck and breast, like in a 1st-winter. The legs are bluish-green, and the bill is bluish-green with a thick black band.
2nd-summer
Like a 1st-summer, the bird doesn't moult much between winter and summer. However, a 2nd-summer completely loses it's head markings, and the bill becomes more yellow with a thin dark band.
Adult winter
In adult winter plumage, The bird has a complete white trailing edge to the wing. The wing is completely grey other than the black wingtip with a large white "mirror" on the primaries. The head and neck are marked brown, but the breast and flanks are clean. The legs are yellow-green, and the bill is bluish-green at the base, with a thin black band in the middle and a yellow tip.
Adult summer
Adult summer plumage is very similar to adult winter, however the head and neck are white, the bill is fully yellow and there is a thin red eye-ring.
Similar species
Ring-billed Gull
A Ring-billed Gull is extremely similar to a Common Gull. It is almost only found in the winter in the UK, and so I am only doing a comparison of 1st-winter, 2nd-winter and adult winter plumages. In all these plumages, the bill is stouter and thicker with a more curved upper mandible, the bird is slightly bigger and bulkier overall and the grey colour is lighter.
1st-winter
Most 1st-winter Ring-billed Gulls would have a paler back than a Common Gull. Many would show additional tail markings to the thick terminal band, and the greater coverts would be the same colour as the back of the bird, showing a contrast with the other wing feathers. Generally, there is more head, neck and breast marking on a Ring-billed Gull. The light window in the primaries is much paler and more obvious, and the tertials have a thinner white edge, making the white "tertial crescent" seen when the bird is perched much thinner and less obvious.
2nd-winter
Again, a 2nd-winter Ring-billed is much paler on the back and wings than a common. Many individuals show dark spots or a partial terminal band on the tail. There isn'y an obvious white trailing edge to the wing, and there are often dark marks on the outer secondaries. The white "mirror" on the primaries is very small or absent, and the "tertial crescent" is very thin. Many individuals have a pale iris.
Adult winter
An adult winter bird can be separated on ways stated before - paler back and thin "tertial crescent" - but also the pale iris can be used. The white primary "mirror" is much smaller than you would expect on an adult Common Gull, and the bill pattern is different - more yellow with a thick black band.
Mediterranean Gull
A Mediterranean Gull is smaller and daintier overall, and is only similar to Common Gull in juvenile and 1st-winter plumage.
Juvenile
A juvenile can be told from a Common Gull juvenile by the darker legs and fully dark bill. The scapulars have much more obvious white fringes and the underside is more plain. The greater coverts are light grey, causing an obvious contrast in the wing.
1st-winter
A 1st-winter is only easily confused when seen in flight, when the contrast with the greater coverts is obvious. The underwing is unmarked, and the black terminal band on the tail is thinner. The tail has few other markings. Also, the back is much lighter than a Common Gull's.
