1CY COMMON GULL
In juvenile plumage, the forehead, throat and nape are white, with the ear-coverts and crown streaked. The streaks of the hind-neck often create a collar, running down the sides of the breast into mottled upper-breast and flanks. The belly and vent are white. In nominate canus, the upper-tail coverts and rump are white with ill-defined chevrons. The under-tail coverts are white as well, some with arrow-heads. The scapulars and mantle feathers are buffish-brown centred with a pale fringe, creating a scalloped effect. The tertials and inner three or four greater coverts are brownish centred as well, with a pale buff fringe. The central and outer greater coverts are more extensive grey-brown, although the feathers have dark shafts and wedge-shaped centres. The median coverts, lower lesser and lesser coverts have brown centres, a dark shaft and buffish fringe, creating a dark carpal bar, contrasting with the pale greater coverts. The dark secondaries create another dark bar on the upper-wing. The secondaries have a white trailing edge, running further onto the inner five primaries. The four to five inner primaries show pale inner-webs; the outer primaries and primary-coverts are all dark. The axillaries and under-wing coverts are white based with black tips, creating lines over the under-wing. The tail-band is clear-cut in nominate canus, with the outer tail-feathers largely white. In the race brachyrhynchus the base of the tail-feathers is mottled, looking completely dark from a distance. Brachyrhynchus has very obvious patterned juvenile upper-tail coverts. 

The partial autumn moult (moult into so-called "first winter"  plumage) includes the body and head feathers. This moult starts as soon as the nest is abandoned and continues to late September in nominate canus. The race heinei, which breeds on northern latitudes may appear all juvenile well into December. The head and breast are moulted to second generation feathers, most reminiscent of the juvenile feathers. The mantle and scapulars are moulted to plain grey second generation feathers in canus.
Brachyrhynchus in 1cy looks paler on average and more washed-out than nominate canus. In canus, the second generation scapulars and mantle feathers are plain grey; in brachyrhynchus, these feathers are often mottled pale brownish, lacking most of a grey tone. The differences between the two taxa become more striking in the first months of 2cy, when the complete wing looks faded in brachyrhynchus, washed brown, including the primaries. The tail will be brownish as well, lacking a clear-cut tail-band as in canus. Brachyrhynchus has the base of the tail-feathers mottled. In general, the upper-tail coverts, head, under-parts and rump are more uniform brown-grey. 

2CY COMMON GULL
The next moult is a partial moult in spring. It starts in February and is completed by April, leaving birds in so-called "first summer" plumage. The head turns much whiter, with the white chin, throat and breast white and dark streaking confined on the crown, hind-neck. The tertials, wing-coverts, primaries and tail-feathers are excluded from this moult and turn paler, the grey parts turn almost white and very worn at the tips. The dark primaries and the lesser coverts start to bleach to pale brown. The second generation grey scapulars create a saddle. The legs are greyish.

From June to October, a complete moult will bring birds in so-called "second winter" plumage. The head and hind-neck are strongly spotted and from the hind-neck, these spots form streaks, creating a collar running down the sides of the breast. Under-parts, tail-coverts and rump are white. The second generation primaries resemble adult primaries, but the black is more extensive in the outer-wing, with black sub-terminal markings down to P4 or even to P3. The greater and median primary coverts and the lesser coverts in the carpal edge are dark centred as well. The white tips on the outer primaries are ill-defined, wearing off quickly and the mirrors on P9 and P10 are smaller than in full adult plumage. The tail is all-white in race canus. The iris is brown, the greyish bill has a clear black bill-band. 
After the complete moult in June to October, brachyrhynchus may still show several immature feathers in the wing. The central tertials and some of the tail-feathers may show dark immature centres (even creating some kind of a tail-band in some individuals). Immature features can also be found in the central greater coverts and in the carpal edge and can even be found on the upper-tail and under-tail coverts. These immature features are less often found in nominate canus, which show no vestiges of a tail-band from autumn 2cy onwards ("second winter" plumage and later). In this respect, brachyrhychus resembles Ring-billed Gull, L. delawarensis. From autumn 2cy onwards, the iris in brachyrhynchus may turn obvious pale.
The race kamtschatschensis shows similar amount of patterning after the complete moult as brachyrhynchus, with many immature markings in tail, tertials and wing-coverts. Moreover, (all?) kamtschatschensis still shows black tips on the white under-wing coverts. 

3CY COMMON GULL
The next moult is a partial moult in spring. It starts in February and is completed by April, leaving birds in so-called "second summer" plumage. The head turns white, with only a few dark markings in some birds. The small primary tips wear off and the black areas turn paler, brownish.

From early summer to October, a complete moult will bring birds in so-called "third winter" or "adult winter" plumage. The head is white with spots, most densely in the hind-neck. The under-parts, tail-coverts and rump are white. The upper-parts are medium grey, with broad white fringes on the tertials. The third generation primaries and later the adult primaries have a clear-cut black triangle on the outer-wing. Black sub-terminal markings run down to P6 or P5. From P1-P9 the primaries show extensive white tips and the two mirrors on P9 and P10 are obvious (there may even be a small mirror on P8). The iris is brown, the bill is yellowish with a faint black bill-band and the legs are yellowish, greenish or greyish, often with a flesh-coloured hue.
In adult winter, brachyrhynchus develops only diffuse head streaking, creating a diffuse grey head and no dark bill-band, whereas canus often has the head strongly mottled or streaked and often develops a full bill-band in winter. Furthermore, the iris in brachyrhynchus is paler, sometimes clear yellow.

ADULT COMMON GULL
The next moult is a partial moult in spring. It starts in February and is completed by April, leaving birds in so-called "adult summer" plumage. The head turns white, with a red orbital ring. The bill turns all yellow or yellowish-green. In summer, head, neck, tail and under-parts are completely white. The upper-parts are medium grey. The outer primaries are black with large white tips. The inner primaries and secondaries are pale grey with a white tip, creating a white trailing edge. The white crescents on the tertials are very broad.
Adult brachyrhychus normally have a black sub-terminal band on P5-P10. Between this black band and the grey centre, a large white spot is visible both from above and below on P5-P7, creating a string of pearls on these primaries. P9 and P10 show large white mirrors.

Measurements in mm's: wing canus: 320-385 (Dwight), 321-380 (Birds of West. Paleartic III), tail: 124-148, bill: 30-38, tarsus: 48-58; n = 16 (Dwight, 1925); 
wing heinei: 351-395 (BWP III); 
wing brachyrhynchus: 328-366 (Dwight 1925);
wing kamtschatschensis: 365-412 (BWP III).