nominate Lesser Black-backed Gull (L. f. fuscus)

(last update: 10-11-2014 )

adult fuscus: July

The grey invasion:
"increase of pale-backed Lesser Black-backed Gulls in the heartlands of nominate fuscus."

One of the major difficulties in gull identification is separating adult Scandinavian intermedius from Siberian heuglini. Variation in plumage of intermedius can be studied along the Atlantic migartion route and in their colonies (there are extensive ringing projects in S Norway and in Denmark, but heuglini is nowhere really abundant. Best place seems to be the near East, especially Israel, and the Gulf states. But what we find there, is that really all heuglini? Sure it is the most common 'slaty grey' Lesser Black-backed Gull, but ring readings indicate one has to careful. Below some example birds.

Heuglini adult, April 17 2006, Tampere, Finland (Hannu Koskinen). Full sub-terminal band on P10, mirror on innerweb of P9. Black reaches to primary coverts at P8-P10, 6 primaries with sub-terminal black.	Heuglini adult, February 2009, United Arab Emirates (Chris Gibbins). Full sub-terminal band on P10, no mirror on P9. Black reaches to primary coverts at P9-P10, 7 primaries with sub-terminal black.
Heuglini adult, March 16 2010, Ashdod, Israel (Amir Ben Dov). Black reaches primary coverts on P7-P10. Small mirror on P10, no mirror on P9. Sub-terminal black on 7 primaries.	Heuglini? adult, March 09 2010, Ashdod, Israel (Amir Ben Dov). Black reaches primary coverts on P6-P10. Full sub-terminal band on P10, no mirror on P9. Winter streaking 'spread out' over head.
Heuglini? adult, January 14 2011, Eilat, Israel (Avi Meir). Different from N European birds in having a long square-ended tongue on underside of P10, and black reaches primary coverts only on P9-P10, not on P8.	Heuglini? adult, February 04 2011, Ashdod, Israel (Amir Ben Dov). Different from N European birds in having large mirrors on P9 and P10; black reaches primary coverts only on P10.
White spot is the colony of Ivanovo Oblast, the answer to all our questions. This location holds colonies where large white-headed gulls show various phenotypics. Some birds strongly resemble cachinnans in upperpart grey tone, head and bill shape, wingtip pattern and call, while other birds strongly resemble argentatus, heuglini or barabensis.	Heuglini-type, June 2008, Ivanovo Oblast, Russia (Greg Neubauer). Much black in outer primaries, sub-terminal black on P4, slate grey upperparts. Note irregular moult sequence. What is the potential for birds from this district to turn up in SW Finland or in Israel?
Heuglini-type, June 2008, Ivanovo Oblast, Russia (Greg Neubauer). Much black in outer primaries, sub-terminal black on P4. A good match to the descriptions of Buzun.	Heuglini-type, June 2008, Ivanovo Oblast, Russia (Greg Neubauer). Much black in outer primaries, sub-terminal black on P4, slate grey upperparts. Inner primaries dropped.
Fuscus CYHP 6CY, May 01 2008, Tampere, Finland (Visa Rauste). Famous pale-backed bird from SW Finland. Full sub-terminal band on P10, tiny mirror on P9. Black reaches to primary coverts at P7-P10, 7 primaries with sub-terminal black.	Fuscus HT-274.520 5CY, April 11 2014, Ashdod, Israel (Amir Ben Dov). Compare upperpart grey tone to average fuscus in Israel. Finnish west coast may have very low numbers of intermedius breeding (2014: 1 pair recorded, and single pale-backed birds observed at Tampere).
Intermedius J4TV 4CY, October 09 2014, Ashdod, Israel (Amir Ben Dov). Probably a minority of N Norwegian pale-backed birds follow an eastern migration route. It remains unknown if these birds are offsprings of pale-backed x dark-backed parents. Anyhow, J4TV illustrates not all pale-backed birds in Israel are heuglini.	Intermedius? U0JD 6CY, March 13 2014, Ashdod, Israel. Pictures: Amir Ben Dov. Recorded many times, and moult strategy first indicated fuscus, but very barred as immature and now pale-backed as adult. Then presumed to be odd heuglini, until recorded in Poland in spring, probably on its way to N Scandinavia? What do offsprings from pale-backed x dark-backed parents look like? Well, probably as U0JD?
Heuglini? adult, August 06 2002, Tampere, Finland (Mars Muusse). Could represent the paler end of fuscus (so not heuglini), or, considering the pot-bellied, short winged appearance, is this intermedius influence in core fuscus breeding area?	Heuglini? adult, August 07 2002, Tampere, Finland (Mars Muusse). Another 'in-between' bird, showing features of both heuglini and intermedius, or could be illustrative for N Norway where both pale-backed and dark-backed birds breed together? Interestingly, in recent years, some ringed pullus within core fuscus area, turned out to be rather pale grey (near)adults.
Intermedius NOS 4196745 19CY, August 25 2012, Boulogne-sur-Mer, NW France (Jean-Michel Sauvage). Upperpart grey tone can be almost blackish in intermedius, with a brown hue on old feathers; different from the blue hue on heuglini upperparts.	Intermedius J5YL 4+CY, October 14 2012, Westkapelle, the Netherlands (Pim Wolf). Full sub-terminal band on P10, no mirror on P9. Black reaches to primary coverts at P7-P10, 7 primaries with sub-terminal black.
Intermedius VC5M adult, June 18 2010, Hirsholm, Denmark (Kjeld Tommy Pedersen). Full sub-terminal band on P10, small mirror on P9. Black reaches to primary coverts at P6-P10, 7 primaries with sub-terminal black.	Intermedius NOS 492441 25CY, November 15 2010, Westkapelle, the Netherlands (Pim Wolf). Full sub-terminal band on P10, small mirror on P9. Black reaches to primary coverts at P8-P10, 7 primaries with sub-terminal black. Winter streaking 'spread out' over head.

Resting flock of fuscus at Tampere dump, Finland.

Bulldozer at household waste, with dominance of argentatus and ridibundus.

Biowaste I: favored place by fuscus.

Primary moult

The moult sequence in nominate Lesser Black-backed Gull Larus fuscus fuscus was already described by Stresemann & Stresemann in 1966 in Journal für Ornithologie. They described a periodische Staffelmauser, a step-wise moult. Normally, large white-headed gulls in Europe start replacement of the remiges during the breeding season and finish this moult in autumn, prior to their migration. Compared to fuscus, this is a relative short distance migration.
Stresemann & Stresemann describe fuscus as an exception as it doesn't start the remiges moult before arriving at the wintering grounds in Africa and the Mediterranean. For a long-distance migrant like fuscus, this seems to be a suitable strategy. This pattern can also be found in long-distance migrants like Terns (Sternidae). 
Stresemann & Stresemann examined skin collections and failed to find any adult L. f. fuscus originating from the breeding or autumn migratory range that was in active primary moult. Therefore they presumed the entire moult stage takes place on the wintering grounds. Adult birds on migration had been collected (Rossitten Bird Observatory, Russia) and these birds confirmed the theses: they must have suspended moult, as Heinroth (1928, Die Vögel Mitteleuropas) concluded: adult fuscus doesn't show active primary moult on migration. They either suspend moult or do not commence moult before arrival on the wintering grounds. 
However, there are a few museum skins that do show adult fuscus in primary moult: the Zoological Museum of Helsinki (not visited by the Stresemanns in 1966) has 21 skins of summer / early autumn birds: 8 are showing moult in the primaries. The museums of Copenhagen and Tring have 10 skins in collecting from the same period: one is showing active primary moult. 

The last decades, the general idea about the renewal of the primaries in adult fuscus has been changed slightly. Field research showed that a small majority (up to 60% in southern Sweden) of the adult fuscus have started to replace the inner one or two primaries on the breeding ground by late August. This primary moult is suspended until arrival at the tropical wintering grounds. Fuscus complete their primary moult in February and March, just before leaving again to the breeding grounds in Scandinavia and northern Russia. By March, the inner primaries may in some birds included in the primary moult, in a second wave. This seems to be a common feature in sub-adults.

Hario and primary moult in fuscus

An interesting article about primary moult in Finland has been published by Ornis Fennica (61/1984): Onset and pattern of primary moult in the Lesser Black-backed Gull Larus f. fuscus - a comparison with the Herring Gull, written by Martti Hario. Hario, working for the Game & Fishery Institute in Helsinki, did a four year investigation (breeding seasons of 1980-83) in the outer archipelago of the Gulf of Finland, 25 km SE of Helsinki (60.07N-25.25E). This archipelago hosts a small mixed colony of fuscus and argentatus, with about 25 pairs of both species, but steadily declining numbers of fuscus. Systematically, shed feathers of both fuscus and argentatus were collected from the time eggs were laid up to September. During the visits, the number of birds were noted and the breeding success was studied in detail. By collecting the shed primaries systematically, Hario was sure about the feathers being shed very recently (he worked on a daily basis for most of the period). To draw his main conclusion, Hario plotted the length of the newly shed primaries against time (n = 337 for argentatus, n = 137 for fuscus) to get a linear regression analysis. 
From early May argentatus shed primaries, starting with the innermost primaries, P1, P2, etc. until P10 is dropped. This is clearly demonstrated by the length of the shed primaries Hario collected; getting longer as time progresses. The first collected primaries in May are about 180 mm in length, the last shed primaries, collected in early August are about 280 mm and clearly apply to the longer outer primaries. From early August onwards, adult argentatus normally abandon the colony and may still have the old outermost primaries present.
The figure for fuscus is completely different with the length of the shed primaries staying more or less the same over a period of three months (regression coefficient only 0.05, with coefficient for argentatus 0.89). Thus, fuscus only moults the short inner primaries in the study area in southern Finland, probably primaries P1, P2 and occasionally (?) P3. Moult is then interrupted or continued outside the study area. 
Argentatus left the colony in the study area as the young fledglings were leaving the area. Fuscus on the contrary remained in the area, despite the poor breeding results and stayed up to the end of August; last birds were seen mid-September.

Hario found no statistical difference in feathers from left or right wing. Hence, birds moulting P1 or P2 (and occasionally P3), the average number of birds shedding primaries would be 17 or 9 (or 6) respectively. From table 1, one may conclude this represents 34% or 18% (or 12%) of the fuscus population in 1980-1983. This is a minority, but substantial number of adult fuscus.

Hario didn't only check the timing of moult, he also noted the patterns of primary moult. He collected newly shed primaries of fuscus and argentatus and as expected, the primaries of argentatus were pretty worn, being almost a year old. Remarkably, this wasn't always the case in fuscus. Some shed inner primaries were very fresh, with the clear white tip still visible. This is so remarkable, considering the much longer migration route for fuscus and the exposure to desert sun in the equatorial summer. The difference in wear suggest a difference in age of the feathers. Hario found only small numbers of intermediates. Exactly in line with the findings of Stresemann & Stresemann's 'periodische Staffelmauser'. Hario estimates the fresh primaries to be only 1-2 months of age, which is the time interval between arrival at the breeding grounds and completion of the second moult wave in the inner primaries. Thus the fresh primaries belong to birds having moulted stepwise, and the worn ones to those having moulted 'normally'.

The proportion of birds moulting stepwise average 20% of the moulting adults. As demonstrated earlier, about 18-34% (lower limit may be 12%) of adult fuscus shed primaries by late summer - early autumn but the proportion of stepwise moulting birds in the total population can be estimated as the moult strategy in non-moulting birds is unknown.

In discussing the primary moult of adult fuscus on the breeding grounds, Hario questions whether fuscus may start moulting earlier because of the great loss of chicks and the poor breeding success. About 90% of the fuscus chicks had died before the start of the primary moult in adults. Nevertheless, the commencement of the primary moult takes place with a one-month time gap and there are no indications adults start moulting earlier and stays the same as in the 1960's. Barth, who based his findings on samples from 1962-1970 draws the same conclusion: primary moult starts at earliest from mid-July and commonly on August 10. But there is a slight change that, given the 'surplus' time between failed breeding and migration, fuscus may start the primary moult earlier in the next generations. For a summary of Barth's article, click here.

The survey on primary moult in adult fuscus was repeated by Lars Jonsson on Gotland. In his article "Baltic Lesser Black-backed Gull Larus fuscus fuscus - moult ageing and identification" in Birding World 11-8 1998 he mentions this research op page 303.
"I have systematically checked fuscus resting at the southern top of Gotland for primary moult from July through to mid September and have found that 60% of the fully adult-looking birds have started the renewal of their innermost one or two primaries by the end of August". 
He doesn't enlarge upon these figures and there is no table included showing total numbers included in this survey, but the '60%' is substantial larger than the '25%' estimation of Hario. A few factors may have influenced this estimation:
- Jonsson's research extended much longer, into September, and may have included birds commencing primary moult in a later stage.
- Jonsson included all adult-looking birds, and he may have included near-adults as well. Near-adults may still start the renewal earlier than true adults. Hario, checking breeding adults in the colony, had probably lower numbers of 4cy and 5cy birds.
- Jonsson's research was done in the mid and late 90's, and, given the poorer and poorer breeding successes for fuscus in the last decades, there may be a minor shift in moult strategy due to 'surplus energy and surplus time', as was questioned by Hario in the early 80's.