Lesser Black-backed Gull (graellsii & intermedius)

(last update: 14-11-2017 )

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lbbg adult January
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lbbg adult October
lbbg adult November
lbbg adult December

sub-adult (4cy / 5cy): October

In this section we include LBBG in 4cy and 5cy. Some very hard to age 3cy may be present as well. 

Movements and origin

By October, all LBBG have left the colonies and surrounding feeding grounds near the Maasvlakte (the Netherlands) and migrate south towards France, Portugal and Morocco. In November and to a lesser extend December, a couple of hundreds remain on continental NW Europe, as north as the south of the Netherlands along the coast at Westkapelle, 65 km south of the Maasvlakte (see map). As it seems, every year a larger group of LBBGs stay "at the most northern latitude as possible", i.e. migrate south only when winter conditions force them to.
Ringed individuals can be found until late November (e.g. year 2000, a rather mild winter until mid-December) and they originate from Scandinavia, Denmark, the Netherlands, Belgium and the U.K. When winter really starts in December, these groups move south to unknown wintering grounds, probably the Atlantic coast of West and South-West Europe.

Identification of sub-adults

Sub-adult LBBG resemble birds in full adult plumage, especially in the grey upper-parts and all-white under-aprts. 4cy LBBG may show all grey wing-coverts and scapulars and, like full adults, may have a white mirror on the old P9 and P10 and a relatively low primary moult score. Normally, 4cy birds have the tail all white by October. However, most sub-adults show immature features to various extends, with sometimes some lesser coverts still immature (brown centred feathers in the carpal edge), extensive dark centres in the central tertials and sometimes some diffuse patterns on the greater coverts. Strongest clues for immaturity are the very well-developed winter-hood in some birds, the well-developed black bill-band and immature coloration of soft parts: bill, iris and legs. Note however that many sub-adult birds have moulted wing-coverts and have shed the outer primaries, becoming similar to birds in adult plumage. Best clues for identification are often found in the old feathers.

The difficulty in identification between 3cy and 4cy birds is nicely illustrated by a 3cy intermedius LBBG ringed 4272452 Copenhagen. It's advanced in upper-part coloration, but note also that P8 is slightly longer than P7, while P9-P10 are still old; moult will probably be arrested at P8. This bird was ringed on July 07 1999 at Langli Ho Bugt Vadehavsoerne, Western Denmark (55.31N,08.19E).

Moult stage and strategy in sub-adults

The complete moult of sub-adults follows the timing and strategy of adult birds, although this timing is a few weeks earlier. By October, the overall picture is somewhat clouded by the mixed flocks of birds originating from British graellsii colonies to Swedish intermedius colonies. By clicking the first thumbnail, you'll find three birds from the Dutch Maasvlakte colony with a very similar moult pattern. 

The complete moult in these three birds has almost been completed with the median and greater coverts replaced. The upper tertials are replaced as well but the lower tertials and the inner secondaries are still old. The new feathers appear shiny dark grey. The old feathers are brown bleached and worn at the tips. The outer primaries P9 and P10 may still be present but the more advanced birds have all the outer primaries shed and in these birds P9  may already be longer than P8. These advanced birds have the secondary moult completed as well. The tail is new and completely white in almost all birds and may show a little wear in the tips already in some birds.

Arrested moult in  immature LBBG

Some sub-adult LBBG may arrest or suspend the primary moult in autumn. Most observations of LBBG with arrested or suspended moult in continental NW Europe apply to immature birds, both in spring and in autumn. The bottom four images show birds with arrested moult. 

One may wonder about the extend of this phenomenon in intermedius and graellsii LBBG. Peter Stewart, who caught many adult LBBG in Britain found quite some birds with arrested moult in summer and we assume adults may arrest the moult for the high energy demand and efforts in defending territories and raising young in summer.

Peter Stewart comments on arrested moult in LBBG: "You have written that arrested moult is a rare phenomenon in both graellsii and intermedius. This is incorrect. It is quite normal, and here in the UK suspended moult is obvious in many adult birds we catch, mainly from June to July. These birds replace only a single primary at a time and can be found with up to suspended P3. Many other birds caught during the same period are about to suspend or resuming moult after suspension by dropping the next primary. We have also found adults birds in April with suspended P1, and these birds are obviously commencing primary moult and suspending in winter quarters, as we have yet to find a bird that has started primary moult in February and March in the UK."
"Suspended moult, especially involving inner primaries, is not obvious in the field and easily overlooked, especially on birds that show little wear on old primaries. Most earlier researchers have overlooked suspended moult, hence the belief that some birds have yet to start their primary moult, and provide later starting dates for the onset of moult. I have some 4500 moult scores for adults, and recorded 183 different primary moult patterns for adults, with a total of 201 different patterns for all age groups. Sick and injured birds in captivity, can also behave differently and can also suspend at odd times." More about Peter's research can be read here. 

Except that birds may be ill or injured, another reason for autumn birds arresting the moult is migration. It's highly inefficient to migrate over a long distance with a gap in the wing. For this long migration, the inner primaries seem to be of high importance, and that may support the general picture observed in the field: if possible, at least the inner primaries are moulted before departure takes place. Of course, the next very good reason is lack of time to fully complete primary moult, but in sub-adult birds, this could be avoid easily by an earlier commencement of the primary moult. M. Hario, doing research on fuscus LBBG in S Finland, scored primary moult in adult birds. Breeding success was very low in his research area, leaving the adult with a lot of "surplus time" and "surplus energy" now the nests were destroyed or the young died. Nevertheless, most birds remained to develop the original moult strategy and timing. More about Hario's research can be read on this adult fuscus page.

Over the past two decades, the use of satellite transmitters to monitor the meso- and large-scale whereabouts of terrestrial, aquatic and aerial vertebrates has greatly enhanced our understanding of species’ ecology and environmental interactions (eg Priede & Swift 1992, Kenward 2001). As the size of transmitters has decreased over time, the range of animals studied has been extended to progressively smaller species, and attachment periods lengthened, further enhancing our knowledge of the movements of migratory birds (eg Gauthier-Clerc & Le Maho 2001, Irsch 2006).

Lesser Black-backed Gulls Larus fuscus breed throughout the northern parts of the Western Palaearctic (del Hoyo et al 1996). As part of a study focusing on the regulation of the migratory behaviour of two Lesser Black-backed Gull subspecies breeding in northern Europe, L. f. fuscus and L. f. intermedius, a number of fledglings were equipped with satellite transmitters (Pütz et al 2007). Here, we report on the results from one of the birds, tracked from fledging over a period of five years until adulthood.
The Lesser Black-backed Gull fledgling was captured on 19 July 2001 in a breeding colony at Bogø, Lillestrand, Fyns Hoved (55° 35’N 10° 36’E), Denmark and was held in captivity with conspecifics until 22 August 2001 to ensure it was in sound condition to be released. On 19 August 2001 the gull was equipped with an 18 g solar satellite transmitter (Microwave Telemetry Inc., USA) harnessed to its back using 6 mm Teflon ribbon. The satellite transmitter was programmed to transmit with an duty cycle of 10 h on/20 h off at a repetition rate of 60 s.
Location data were received through the Argos satellite system and categorised into seven location classes (LC) with increasing accuracy: Z, B, A, 0, 1, 2 and 3. Of the 1,782 co-ordinates received by 17 June 2006, only 5.8% were accurate to within 1 km (LC 1, 2 and 3), whereas all others were associated with unknown errors to be defined by the user in location classes 0 (22.6%), A (22.7%), B (45.8%) and Z (3.2%). This was mainly due to the low power of the satellite transmitters and the high electromagnetic interference in the area studied. Therefore, all locations received in one particular area were averaged with separate calculation of the standard deviation for longitude and latitude, resulting in elliptical areas most likely used by the bird during specific periods. A more rigid approach to validating individual positions was impossible due to the generally low quality of data, the fact that transmissions incorporated a duty cycle, and the complete lack of positional data for a number of duty cycles, which left quite large gaps in the tracks, especially when the bird was migrating. For the same reasons it was impossible to calculate specific behavioural parameters such as, for example, flight speeds.

After releasing the bird at its natal site, it remained in the area before migrating southwards in early November 2001 (Table 1). During this first migration, the bird rested twice (in total > 25 d) in Germany, once to the north of Magdeburg and then to the south of Hannover, before flying southwest over Switzerland and southeastern France (Fig 1). The gull then crossed the Mediterranean Sea and wintered to the east of Jijel on the Algerian coast. This area of about 8,000 km² was also used in subsequent years for wintering (Fig 1), except for 2005/06 when it shifted to the west over an area of 14,000 km².
In spring 2002, the bird headed northeast, crossing Sardinia and Corsica before turning northwest on reaching the Italian coast. It eventually arrived in northern France near Lens, where it spent the whole summer. In the autumn the bird headed southwards to the Algerian coast, crossing the Mediterranean via the Balearic Islands. Thereafter, the gull maintained this route, with small deviations, when migrating between its summering and wintering areas, and major behavioural changes occurred only with regard to the summering area. In 2003, the gull migrated again towards Lens, but then continued northeastwards to the central Netherlands, from where it returned to northern France at the end of the summer. In 2004 the bird travelled more extensively in a stretch 250 km wide along the coasts of Belgium, the Netherlands, Germany and Denmark (Fig 1).

As in 2003, the bird returned to northern France towards the end of the summer to migrate to the wintering area. A comparable strategy was apparent in 2005, but the bird migrated first to its natal site in Denmark before moving along the North Sea coast, this time less far inland than in 2004. As in previous years, towards the end of the summer the gull moved to northern France before migrating into its Algerian wintering area. In 2006, the bird flew straight to Denmark, where the last location was obtained on 28 September 2006 before transmission ceased temporarily until 18 March 2007. Since then location data have been received only occasionally and are not considered in this context.

During the study, the bird was resighted twice in northern France (Harry J.P. Vercruijsse, pers comm), first on 10 October 2002 at 50° 20’N 3° 10’E and again on 11 August 2005 at 50° 41’N 2° 24’E, both observations occurring in areas where, according to calculations for these particular periods, the bird was resident. This also to some extent supports our approach of working with the high number of low-quality locations received. Unfortunately, and despite some efforts, the bird was not resighted at its breeding grounds.

Arrivals at and departures from the wintering area on the Algerian coast occurred progressively earlier, from early December to early November and from late May to late March respectively (Table 1). The same pattern was apparent in arrivals to and departures from the summer area, where the arrival shifted from early June to mid April and the departure from early November to early October. Concurrently, periods of active migration became progressively shorter, but were still subject to considerable variation. No particular stopover sites could be identified.

Satellite telemetry has opened a new chapter in the study of bird migration by enabling the movements of specific individuals to be monitored continually (eg Gauthier- Clerc & Le Maho 2001, Irsch 2006). The results obtained in this study represent, to our knowledge, the longest monitoring period worldwide – five years from fledging to breeding – for a bird with a body mass of less than 1 kg. To date, only White Storks Ciconia ciconia have been tracked for comparable time and life-history periods, one study covering seven years (Aebischer 2005) and another four years (Chernetsov et al 2005). Long-term satellite tracking of adult birds has so far been restricted to only a few larger species, mainly Ciconiiformes and birds of prey.

For example, one White Stork has been successfully tracked for 10 years (Berthold et al 2004), one Bald Eagle Haliaeetus leucocephalus for over seven years (Watson 2005) and several Ospreys Pandion haliaetus for periods of up to four years (Hake et al 2001, Alerstam et al 2006). Future technical developments will undoubtedly enable researchers to successfully track a greater number of much smaller species for longer periods, while at the same time more, and more accurate, positional fixes will likely be obtained.

Knowledge of the migratory behaviour of Lesser Blackbacked Gulls of the subspecies L. f. intermedius is still quite sketchy, despite decades of ringing effort. Apparently, birds from this subspecies migrate predominantly southwest along the European coast to winter along the Atlantic coast from France to Mauritania (Bakken et al 2003, Bønløkke et al 2006). Although it remains speculative whether the behaviour of one individual is representative, this study highlights the potential of long-term monitoring of migratory birds. More intensive research should be able to establish life-history parameters on an individual basis and, provided a sufficient number of individuals have been successfully tracked, for whole populations.

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Belgium: graellsii 'Dutch intergrade'
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Arrested moult in  immature LBBG
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