Plate 1: Herring Gull argenteus juvenile, August 23 2016, Katwijk, the Netherlands (Mars Muusse). White lines surround the feather tracts.
Just below the neck is the mantle, forming a small triangle. They comprise small feathers, and don’t play a role in this context. Below the mantle you’ll find the scapulars, often an obvious place for moult commencement in a juvenile gull. Mantle and scapulars are commonly refered to as 'the back'.
There are 6 tertials which extend into the row of 18 secondaries. In a folded wing, we normally only see the very tips of these secondaries, but in this picture, after stretching, more of the secondary feathers is visible.
Secondaries are covered by three groups of wing-coverts: greater coverts, median coverts and lesser coverts. In a stretching bird you’ll notice the greater coverts adjacent to tertial #1 are closest to the body, therefore called ‘inner greater coverts’. The outermost wing-coverts are hidden behind the flank feathers in this resting bird.
Juvenile Herring Gulls have blackish brown outer primaries with small white tips (which wear off easily within some weeks). The arrow points to primary #7 (P7). The small last tip is of P10. The tail is visible below P7 in this resting bird.

Plate 2: Herring Gull 2CY, April 25 2017, Katwijk, the Netherlands (Mars Muusse). It's the end of April and this bird is in deteriorated plumage. Note the abraded condition of the feathers.
Complete moult has not started yet as the innermost primary P1 is still present, but not for long anymore. New feathers are more than welcome.

Plate 3: Herring Gull argenteus A||V 2CY, April 23 2017, Katwijk, the Netherlands (Mars Muusse). The complete moult has commenced last week. In the picture you can count back from P10 inwards, and you’ll end at P2 in this bird. This explains the small moult gap between primaries and secondaries: P1 is missing. From now on the worn plumage will be replaced entirely.

Plate 6: Lesser Black-backed Gull graellsii Z||P juvenile, September 03 2016, Utrecht, the Netherlands (Mars Muusse), together with 2CY Lesser Black-backed Gull (unringed) for comparison (same location, same day).

How to recognise the juvenile plumage, in late summer?
That is pretty easy, and most field guides show the juvenile plumage. The picture illustrates a juvenile (left), and 2nd cycle bird (right) that is one year older and is in active complete moult (PB2 moult) into 2nd basic plumage. Characteristics are:
.1 All scapulars are juvenile; a dark brown centre and crème-white, notched fringes (1a), while the 2nd cycle bird shows at least a few plain feathers that reveal the grey tone of the adult plumage (1b);
.2 In late summer all wing-coverts are still juvenile and approximately the same age and condition as they were acquired simultaneously (2a). This is not the case in 2nd cycle birds, which have a mix of old and new feathers in the wing-coverts. This is easily explained, as 2nd cycle birds are in moult for over 4 months already (they started late April) and wing-coverts have been replaced in a sequence (not all at once) leaving a visible difference between new coverts and adjacent old coverts;
.3 Juvenile primaries are new and pointed (3a), while 2nd cycle birds have old and new primaries at the same time, and they are still moulting these outer eathers. The moult gap in primaries is more obvious in flying birds.

Plate 8: Type I - Great Black-backed Gull marinus RUM ES17994 juvenile, February 01 2015, Boulogne-sur-Mer, France (Jean-Michel Sauvage). Ringed in N Russia (66ºN).
A few scapulars missing, otherwise a remarkable fresh juvenile plumage by February.

Plate 9: Type I - Great Black-backed Gull marinus 1st winter, February 02 2012, IJmuiden, the Netherlands (Mars Muusse).
Just a few small scapulars replaced, otherwise in fresh juvenile plumage. A crispy Viking, the eternal youth.

Plate 10: Type I - Herring Gull argentatus 1st winter, March 25 2017, IJmuiden, the Netherlands (Mars Muusse). Most scapulars are juvenile (1), and juvenile wing-coverts have neat fringes and no bleaching in brown parts (3). Juvenile tertials still have neat white fringes (4). Moult stage: late March and only a few small scapulars replaced (2).

Plate 11: Type II - Herring Gull argenteus 1CY, Augustus 21 2015, Katwijk, the Netherlands (Mars Muusse). From the local rooftop colony, now at the beach. Post-juvenile moult starts immediately after fledging. Arrows 'nieuw' point to new 2nd generation scapulars growing in. Note the buffish tone of these feathers, the delicate anchor pattern and the crisp fringes.

Plate 12: Type II - Lesser Black-backed Gull graellsii 3:DCY 1CY, October 06 2016, Matosinhos, Portugal (José Marques). Ringed in France. Early October and nearly all scapulars already replaced in a classic sequence, starting with the small upper scapulars (arrow 'nieuw') and the last scapulars to be replaced are the large rear feathers (arrow 'oud'). Note juvenile wing-coverts already worn at the fringes.

Plate 13: Type II - Great Black-backed Gull marinus JP140 1st cycle, December 04 2011, Boulogne-sur-Mer, France (Jean-Michel Sauvage). Ringed in S Norway. The scapulars have been replaced (now 2nd generation), and that's it for this winter. Wing-coverts, tertials, etc will remain juvenile in the Plain Jane strategy.

Plate 14: Type II - Great Black-backed Gull marinus JU818 1st cycle, December 20 2014, IJmuiden, the Netherlands (Mars Muusse). Ringed in S Norway. Less advanced than JP140. Most scapulars are 2nd generation (arrow 'nieuw'), while large rear scapulars are still juvenile (arrow 'oud'). In the tertial tips, the white fringes (which lack pigmentation, hence are more vulnerable to wear) are obviously worn. JU818 was still present in April, still with all wing-coverts and all tertials juvenile.

Plate 15-16: Type II - Herring Gull argenteus A||V 1st cycle, October 03 2016 (left) and April 02 2017 (right), Katwijk, the Netherlands (Mars Muusse). Pictures mirrored.
Immediately after fledging in August, this bird started post-juvenile moult and by October almost all scapulars were replaced. Several 2nd generation feathers already look paler (arrow ‘old 2nd gen’ in left picture), indicating these were replaced some time ago (August). From the left picture it shows the long rear scapulars will be replaced last, they are still juvenile in October (arrow ‘juvenile’ in left picture).

Same bird in April in right image, just prior to commencement of the complete moult (as P1 is still present). This image shows the full extent of post-juvenile moult: the process only included scapulars but no tertials nor wing-coverts, as is classic for Plain Jane. Juvenile feathers are worn and the brown parts are bleached (arrow ‘juvenile’ in right picture).
Eventually the long rear scapulars were replaced, probably somewhere in December (arrow ‘old 2nd gen’ in right picture), and by April some scapulars appear fresher, with an anchor pattern, buffish centres and neat fringes. These are fresh 3rd generation scapulars, and you’ll find them at exactly the locations where we saw old 2nd generation scapulars half a year ago (arrow ‘new 3rd gen’ in right picture).

These two images illustrate that “if you see fresh upper scapulars in spring, while long rear scapulars are replaced for 2nd generation, these new feathers are in fact 3rd generation”. For Plain Jane we write “in spring”, but Type III birds, Speedy Gonzales, may show such 3rd generation scapulars already by December.

Plate 17: Type III - Yellow-legged Gull michahellis ST3U 1CY, November 16 2016, Katwijk, the Netherlands (Mars Muusse). From Croatia. By November all scapulars replaced, together with inner greater coverts, six inner median coverts and about eight lesser coverts (arrows '2e gen'). Outer coverts and tertials still juvenile.

Plate 18: Type III - Caspian Gull cachinnans 431P 1CY, November 16 2016, Katwijk, the Netherlands (Mars Muusse). From Poland. Similar to ST3U from Croatia. Type III birds from S Europe show a rapid and extensive moult in autumn which halts early winter.

Plate 19: Type III - Yellow-legged Gull michahellis 1G6 1CY, November 15 2009, Madrid, Spain (Delfín González). Advanced bird, which has replaced all scapulars and nearly all visible tertials and wing-coverts by November. Just a few juvenile feathers visible in outer greater coverts and outer lesser coverts (arrows '1e gen'). Tail and primaries will remain juvenile throughout winter and no more coverts will be replaced in this post-juvenile moult.

Plate 20: Type III - Caspian Gull cachinnans UKK L001754 1st cycle, January 13 2004, Lubna, Poland (Ruud Altenburg). From Ukraine. Many wing-coverts replaced (left arrow '2e gen' points to complete row of 2nd generation median coverts, right arrow points to 2nd generation inner greater coverts). Upper tertials replaced as well. Tail and primaries will remain juvenile, as will the outer wing-coverts (left arrow '1e gen' points to juvenile lesser coverts, right arrow points to juvenile outer greater coverts).

Plate 21: Type III - Caspian Gull cachinnans HCV93 1CY, November 16 2016, Katwijk, the Netherlands (Mars Muusse). From Belarus, with another, unringed Caspian Gull in front. Both birds show new inner coverts and the front bird also has a new tertial (arrows '2e gen'). If 2nd generation coverts are present, it's often the median coverts that are replaced, as these birds show.

Plate 22: Type III - Lesser Black-backed Gull graellsii S.L 1CY, November 04 2014, Utrecht, the Netherlands (Frank van der Meer). Image is mirrored. An example 'Dutch Speedy Gonzales'. Blue SL replaced nearly all scapulars (left arrow '2e gen') and also several inner wing-coverts (two right arrows '2e gen'). In pattern, and especially in condition, they clearly differentiate from juvenile feathers (arrows '1e gen').

Plate 23: Type IV - Heuglin's Gull heuglini 2CY, June 12 2009, Tampere, Finland (Petri Salo). Tertials and most visible wing-coverts have been moulted. The neat fringes of these feathers indicate recent replacement, in early spring, currently in much better condition that the juvenile outer coverts, which are now about a year old. Extensive moult in late winter result in spring birds in N Europe showing crisp 2nd generation feathers, while complete moult still has to start. This is characteristic for Type IV Beauty Heugy.

Plate 24: Type IV - Lesser Black-backed Gull intermedius JM4E 2CY, June 22 2013, Noordwijk, the Netherlands (Maarten van Kleinwee). From S Norway, recorded in Morocco in winter. Advanced moult in Africa included wing-coverts and the tail. Also note the neat fringes on 2nd generation tertials. Type III Speedy Gonzales has 2nd generation coverts and tertials in June too, but in Gonzales these feathers are much older and already worn and bleached. Accurate ageing of feather condition is essential.

Plate 25: Type IV - Lesser Black-backed Gull intermedius 2CY, June 15 2013, Noordwijk, the Netherlands (Maarten van Kleinwee). In W Europe there is no other taxon showing such advanced moult: in winter all scapulars and wing-coverts were replaced, but also the tertials, all tail-feathers and secondaries. Only primaries remained juvenile before northbound migration. After arrival in NW Europe, the complete moult started at P1, and currect stage is P1-P2 replaced and P3 missing.

Plate 26: Type IV - Heuglin's Gull heuglini 2CY, May 02 2007, Tampere, Finland (Hannu Koskinen). Moult stage is similar to the left bird, but this heuglini has also replaced P10 (some returning Heuglin's Gulls in N Europe show replaced primaries). Essentially, note the very neat secondary feathers and the crisp white-tipped tail-feathers, indicating recent replacement last spring, when the bird was still in the winter quarter. In this respect, spring moult, they are different from Type III Gonzales.

Plate 27: Lesser Black-backed Gull intermedius J221N 1CY, December 04 2015, Matosinhos, Portugal (José Marques). Already December, but scapulars still juvenile, although some moult gaps visible. Apparently, post-juvenile moult is just starting, rather late in the season. Up to this moment J221N is similar to Type I crispy Viking.

Plate 28: Lesser Black-backed Gull intermedius J221N 1CY, December 29 2015, Matosinhos, Portugal (José Marques). Right from the start, moult progresses at high pace: only 4 weeks later and almost all scapulars are replaced. Type IV Beauty Heugy commence post-juvenile moult in mid-winter which continues in spring. We only then will know the full extent of this moult.

Plate 29: Lesser Black-backed Gull intermedius J221N 2CY, January 24 2016, Matosinhos, Portugal (José Marques). Another 4 weeks passed, and now 2nd generation coverts grow in. This picture illustrates that moult is initialised in the inner wing-coverts and upper tertials: a classic view in all taxa.

Plate 30: Lesser Black-backed Gull intermedius J221N 2CY, April 22 2016, Matosinhos, Portugal (José Marques). Wing-covert moult still in progress, and now several tail-feathers are missing. Note the splendid condition of 2nd generation feathers, which still will be obvious when we see such birds returning in N Europe in June. In this respect they differ from Type III Gonzales.

Plate 31: Type IV - Heuglin's Gull heuglini 1CY, December 03 2009, N Oman (Hans Larsson). By early December the first moult gaps in the small scapulars appear in the neat juvenile plumage. This indicates the commencement of post-juvenile moult. Note this late hatching bird from the tundra has a neat plumage lacking obvious wear or bleaching (even in Oman with its desert climate).

Plate 32: Type IV - Lesser Black-backed Gull intermedius J2T9 2CY, March 14 2010, Madrid, Spain (Delfín González). Image is mirrored. All scapulars replaced and now the post-juvenile moult includes wing-coverts. New feathers show neat fringes and a buffish grey tone, obviously replaced recently. And moult is still in progress: note the growing central tertials.

Plate 33: Type IV - Heuglin's Gull heuglini 2CY, February 12 2011, Ashdod, Israel (Amir Ben Dov). By February the juvenile wing-coverts still look remarkable good. All scapulars were moulted in this bird, as were also many inner wing-coverts and upper tertials. Splendid condition of new feathers indicate very recent replacement.

Plate 34: Type IV - Lesser Black-backed Gull intermedius J369N 2CY, May 27 2016, Utrecht, the Netherlands (Mars Muusse). From S Norway. P1 is still present, hence the complete moult still not started (if post-juvenile moult is extensive, then the complete moult starts often quite late in the season). In this standing bird almost all wing-coverts and tertials were replaced for 2nd generation feathers. In flight it appeared the complete tail was included in the post-juvenile moult in winter as well (click image).

Plate 35: Type IV - Heuglin's Gull heuglini 2CY, April 23 2006, Tampere, Finland (Visa Rauste). P1 is still present, hence the complete moult still not started. All replaced feathers are part of the post-juvenile moult: scapulars, many inner wing-coverts and the upper tertials. The excellent condition of these feathers indicate recent moult, in late winter. Moreover, tertial #4 is still growing in this Beauty Heugy.

Plate 36: Type IV - Lesser Black-backed Gull 2CY, May 24 2016, Katwijk, the Netherlands (Mars Muusse). Complete moult not started. When standing, this bird hardly showed any old juvenile feathers, but in flight the primaries and most secondaries appear juvenile. An extensive post-juvenile moult included many wing-coverts and the complete tail. Grey wing-coverts were moulted very recently, like the tail, which has crisp white tips.

Plate 37: Type V - Baltic Gull fuscus 2CY, January 30 2010, Ashdod, Israel (Amir Ben Dov). Replaced scapulars by the end of January, but otherwise this juvenile plumage shows neat fringes on coverts and no bleaching in the brown parts. Type V fuscus comprise late moulting birds, from mid winter to spring.

Plate 38: Type V - Baltic Gull fuscus J007K 2CY, February 01 2014, Ashdod, Israel (Amir Ben Dov). Ringed in Troms, Norway (69°N). Showing active moult in the coverts (arrow '2e gen') and in the tertials. It's still too early to get the full picture of moult extent.

Plate 39: Type V - Baltic Gull fuscus 2CY, March 12 2011, Ashdod, Israel (Amir Ben Dov). P1 is growing, P2 missing, P3-P10 are still juvenile. Sequence of wing-covert moult matches our Herring Gulls in complete moult in summer: growing inner coverts correspond with growing P1.
But there is a difference too: the early replacement of rectrices. Normally rectrices will be replaced when primary moult arrives at P6. Many fuscus replace rectrices rather early in the process.

Plate 40: Type V - Baltic Gull fuscus CSJ4 2CY, April 01 2011, Ashdod, Israel (Amir Ben Dov). Ringed in Finland. All scapulars replaced, the fringes of 2nd generation feathers worn in April. Active primary moult with P4 new, P5-P6 growing, P7-P10 juvenile and simultaneous moult in rectrices. Outer greater coverts are still juvenile, but the wing-covert panel is largely replaced for 2nd generation. Base tone of the feathers is blackish brown.

Plate 41: Type V - Baltic Gull fuscus CSX2 2CY, May 15 2010, Eilat, Israel (Amir Ben Dov). Ringed in Finland. Image is mirrored. Extensive moult on the wintering grounds included all feather tracts. Now there is time and energy for migration, and this advanced bird may soon turn up in Finland again. Detailed analysis reveal small, blackish feathers in the median covert row and scapulars: these are 3rd generation feathers.

Plate 42: Type V - Baltic Gull fuscus C59J 2CY, May 31 2011, Espoo, Finland (Visa Rauste). From Finland. And there it is: 2CY fuscus in northern Europa. All feathers, including all primaries, were replaced in an extensive moult in the winter quarters. Again, like in CSX2, several blackish 3rd generation feathers are present.

Plate 43: Type V - Heuglin's Gull heuglini 2CY, June 14 2002, Syktyvkar, Russia (Visa Rauste). Like the previous Baltic Gulls, this 2CY Heuglin's Gull has replaced all primaries in the winter quarters prior to northbound migration, where Visa took this picture. P5-P10 are 2nd generation blackish primaries now. Meanwhile, a limited moult was started, which result in new adult-like grey wing-coverts growing in (now 3rd generation feathers).

Plate 44: Type V - Heuglin's Gull heuglini 2CY, June 14 2002, Syktyvkar, Russia (Visa Rauste). No active moult in inner primaries, which would be normal this time of the season. This bird too has replaced (almost all) primaries last spring. However, some primaries where skipped in the process: right wing P3 is old, and left wing P3-P4 are still juvenile. In fact, these are the last juvenile feathers on the entire bird.

Anything around? Birds in September.

Plate 45: September 15 2011, Huelva, Spain (Corriplaya). It's September, and already this bird is extensively moulting feathers. This excludes type I, IV and V birds. So, type II or III? Plain Jane can be eliminated easily by the new coverts: arrow 2 points to new median coverts, arrow 3 points to new inner greater coverts. New wing-coverts doesn't match Plain Jane, it has to be Speedy Gonzales.

Check: an early and extensive moult? Indeed, moult in scapulars is very advanced and arrived at the lower scapulars (arrow 1). And we were correct: inner wing-coverts are a different generation, when we compare these inner coverts (arrow 3) to the outer coverts (arrow 4). The inner coverts must be 2nd generation: they are much fresher feathers lacking the wear we see in the adjacent feathers and also the pattern is different. Finally, if 2nd generation coverts are present, we expect them exactly at this location, the inner coverts.
This is a picture of 1CY Yellow-legged Gull michahellis G.12L ringed in Cádiz, Spain.

Plate 46: September 29 2014, Portimao, Portugal (Carl Baggott). The juvenile plumage is slightly worn, with 'moth-eaten' head feathers (arrow 1). Some scapulars (arrow 2) and wing-coverts (arrow 3) have the white fringes worn away. This wear in September doesn't match arctic species (type I, IV of V). And absence of moult eliminates type III, leaving Plain Jane as best option. Hence, a local Herring Gull, Lesser Black-backed Gull or Great Black-backed Gull. A slam dunk: this is a classic Lesser Black-backed Gull on tertial pattern (no notching), outer greater coverts (extensive dark centres), the chocolate brown aspect of the plumage, and broad tail band.

Check: September is too early in the season to determine the full extent of post-juvenile moult. Intermedius Lesser Black-backed Gulls normally start late, but late commencement is also possible in our local graellsii. The worn plumage makes a southern hatched bird slightly more likely, but without ring data this bird would best be labeled 'western Lesser Black-backed Gull'.
R:V3E is a 1CY graellsii Lesser Black-backed Gull, ringed in Portes-en-Re, France.

Anything around? Birds in December.

Plate 47: November 24 2012, Anza, Morocco (Christian Pedersen). Image is mirrored. No 2nd generation feathers present and only slightly worn plumage: we assume a northern origin. Scapular moult is about to start, indicated by some moult gaps (arrow 1). This late start of the moult doesn't match type II and type III birds, and type I birds would only replace a single small feather at most. The full extent of post-juvenile moult is still not clear by November, hence this may be either type IV Beauty Heugy or type V Fussy Fin. On location (Atlantic Morocco) western Lesser Black-backed Gull should be the first choice.

Check: tertial pattern (no notching), outer greater coverts (extensive dark centres), the chocolate brown tone, and broad tail band indicate Lesser Black-backed Gull. Northern birds in Scvandinavia belong to subspecies intermedius. This is 1CY intermedius Lesser Black-backed Gull JR2Y from Troms, Norway (69°N), travelling distance to Anza is 4600 km.

Plate 48: December 20 2014, IJmuiden, the Netherlands (Mars Muusse). Most scapulars are replaced (arrow '2e gen'), but lower scapulars, wing-coverts and tertials are still juvenile (arrow '1e gen'), with worn fringes. This immediately leads to type II Plain Jane as best option. Type I, IV and V are eliminated as they should still have most scapulars juvenile. Juvenile lower scapulars and absence of wing-coverts moult should indicate Plain Jane rather than Speedy Gonzales in December.

Check: This giant, easily swallowing a complete salmon, is a classic Great Black-backed Gull. Probably it's not from the arctic tundra: it's still the first half of winter, and we see obvious wear and tear in the plumage of this bird. White parts of tertials and wing-coverts are heavily worn. We assume a more southern hatching population.
Indeed it is. This is 1CY Great Black-backed Gull marinus JU754 ringed in S Norway.

Anything around? Birds in February.

Plate 49: February 07 2009, Dubai, U.A.E. (Chris Gibbins). The picture shows a bird with replaced wing-coverts which leads to either type III, IV or V. All juvenile feathers are bleached and heavily worn. Note also that all scapulars, including long rear feathers have been replaced. Both lower scapulars and replaced wing-coverts are bleached (arrows 'oud 2e gen') and therefore the feathers must have been replaced months ago, in the hatch year. This is not in line with type IV and type V, which retain a juvenile plumage in the first half of the winter. It is essential to estimate the condition of feathers to get an ID in this bird.

Check: Type III comprises several taxa, including Caspian Gull cachinnans which on location should prevail. The pear-shaped head with long parallel bill also suggests Caspian Gull.

Plate 50: February 09 2013, Calais, France (Jean-Michel Sauvage). Almost all scapulars are 2nd generation (arrow 1); a few long rear scapulars are still juvenile (arrow 2). All wing-coverts and tertials are still juvenile, the white notched parts completely worn away on the latter (arrow 3). This suggests a southern bird, from our latitudes or further south (type II and III). Worn plumage and limited moult can be found in several species: Lesser Black-backed Gull graellsii, Great Black-backed Gull marinus, Herring Gull argenteus or even retarded Yellow-legged Gull michahellis. Broad white bars on the outer greater coverts, together with the notched tertial fringes indicate 1st winter Herring Gull argenteus.

Check: This is 2CY Herring Gull argenteus YUA.C ringed in Belgium, a classic February bird.

Anything around? Birds in April.

Plate 51: April 07 2017, IJmuiden, the Netherlands (Mars Muusse). Note that the entire plumage is still juvenile, only showing single small moult gaps in the scapular region. This, in early April, can only be a crispy Viking.

Check: no tertials and no wing-coverts were replaced, The scapulars are bleached and their fringes are worn, but at the same time we still see many white parts in wing-coverts and tertials.
This is a Scandinavian Herring Gull.

Plate 52: April 24 2010, Eilat, Israel (Amir Ben Dov). Regarding moult, this is the opposite of the Herring Gull, although both birds may have hatched in the same region. All wing-coverts are fresh 2nd generation and the tail is 2nd generation as well (arrow 1). New secondaries are growing in (arrow 2) and primary moult arrived at P7 (arrow 3). This moult scheme reminds us of the complete moult in summer, but now shifted to spring. And that leads to type V: Fussy Fin.

Check: This clearly is a 2CY Baltic Gull fuscus in Israel.