Fig.1. Yellow-legged Gull in adult plumage (5cy), January 2012

Since the mid-1980s Yellow-legged Gull has become a regular visitor to the West Midlands region, with numbers now exceeding 100 individuals annually. There are records for all months of the year but with two distinct arrival periods: in late summer (peaking in July) and during mid –winter (peaking in November and December).  The earlier peak reflects the annual post-breeding moult migration of Yellow-legged Gulls from southern Europe. The source of the gulls involved in the mid-winter peak is less clear but may involve wider geographical origins. The status of the species in the West Midlands region was described in detail in the West Midland Bird Club Annual Report No. 69 (Dean 2004) and is also discussed here.

Many observations of Yellow-legged Gulls (hereafter YLG) are from sites which attract large numbers of gulls, particularly landfill sites, roosts and favoured loafing areas.  At such sites there may be a number of YLGs, some of similar age, which ‘come and go’ and which move between different sites.  Although individual gulls may reside in the region for some time, it is rarely possible to identify and monitor a particular individual with certainty over an extended period.  A rare exception to this has involved a YLG in second-winter plumage which arrived in the southern section of Kingsbury Water Park (KWP) in January 2010, thus just into its third calendar year. Remarkably, it remained for over 14 months before departing, presumably migrating back to southern Europe, but it has returned and resided at the site from late summer through the winter in each successive year to date (2024). Such prolonged presence has provided a singular opportunity to study a known individual. This article describes the results of these studies, based upon regular observations throughout the period of the gull’s presence. Issues examined include its developing phenology (seasonal ‘arrivals and departures’), moult and plumage development (from 3cy to adult), and behaviour (including reactions with other species and with a second YLG).

Phenology

The YLG was first noted on January 20^th 2010, during a brief respite from a prolonged cold spell, which began in mid-December 2009 and had brought heavy falls of snow and freezing of all but the largest and deepest water-bodies. The intense cold returned at the end of the month and persisted through February but the gull remained at the site, frequently standing on the ice. As spring approached, the expectation was that it would soon depart. However, the weeks –and then months – went by and it remained on site. In the event it remained until early April 2011, a remarkable 14 months and more since its arrival. Adding to the surprise, it has returned to the site in each successive year. The periods during which it has been present in each year between 2010 and 2017 are portrayed in Figure 2 (plotted from summer through winter).

Fig. 2. Phenology of an individual Yellow-legged Gull at Kingsbury, Warks, 2010 to 2016/2017

Note that, while the arrival date has been consistently in early- to mid-July, the departure date became progressively earlier between 2011 and 2013 but then became reasonably consistent, between mid-January and early February. Then, it departed in late December in 2020 and 2021.This may reflect the onset of breeding condition, as the bird reached adult plumage and presumably returned south earlier to re-establish a breeding territory.

Appearance, moult and plumage development

When it first appeared, in January 2010, the YLG was in its third calendar year and in what has traditionally been referred to as ‘second winter plumage’ (2W). It is a large and robust individual, presumed to be a male, a conclusion supported by later interactions with an apparent female Lesser Black-backed Gull and later the attentions of a presumed female Yellow-legged Gull (see Behaviour).

Between late June and November 2010, it underwent a complete moult, in the process acquiring its 3W plumage calendar-wise. Interestingly, however, its appearance after this second complete moult was very much as would be associated traditionally with a 4W individual rather than 3W: very like adult apart from black in the primary coverts. The plumage traditionally associated with a 3W bird was effectively 'by-passed' (see Fig. 3g & 3h).

In subsequent years it has progressed into fully adult plumage. In all aspects and at all ages, the plumage has been ‘feather perfect’. However, the legs took longer than anticipated to develop a fully rich yellow hue. It remains unclear whether this was attributable to an unusual diet (residing for so long at an inland site in central England and feeding primarily on fresh-water fish), seasonal factors (leg colour often being rather paler in winter than in the breeding season) or simply individual variation. Observations of other YLG suggests that, while a yellow hue usually becomes apparent from late in the 2cy,  the species frequently takes longer to develop the full yellow hue than the literature sometimes implies. The leg colour of the KWP individual was evidently yellow from 3cy but continued to enrich up to its 9cy or 10cy (see Fig. 19). Coulson (2019, Gulls, New Naturalist No. 139) quoted data from the Isle of May showing that, in the Herring Gull, clutch size (and thus presumably breeding condition) reached a peak in individuals 7 or 8 years old. No doubt a similar regime applies to michahellis and perhaps breeding season hues are also retained longer into the post-breeding season.

Figures 3 present images of the gull, illustrating its moult and plumage development from 3cy (2W) to 5cy (adult), between January 2010 and January 2012.

3cy, January 2010 (2W plumage)	3cy, February 2010 (2W plumage)
3cy, June 2010 (inner primaries dropped)	3cy, July 2010 (2S plumage: head, neck & mantle more adult-like but outer primaries, tertials and some coverts  not yet replaced; bill with extensive yellow)
3cy, August 2010 (at rest quite adult-like but note all-dark primaries and dark marks in tertials	3cy, August 2010 (outermost two primaries yet to be replaced)
3cy, November 2010 (legs with weak yellow hue)	3cy, November 2010 (primary moult complete). Appearance much as associated with 4W rather than 3W: quite like adult apart from black on primary coverts.
4cy, March 2011 (bare parts now approaching adult appearance but legs paler than bill-base)	4cy, April 2011 (note rich red orbital ring encircling eye)
4cy, July 2011 (commencing third complete moult)	4cy, July 2011 (outer primaries old, inner primaries dropped)
4cy, October 2011 (inner primaries new, outer primaries dropped)	4cy, November 2011 (like adult - though black mark persists on lower mandible )
4cy, November 2011 (primary moult nearly complete : p10 just short of full length)	4cy, December 2011 (primary pattern)
5cy, January 2012	5cy, January 2012 (new primaries all fully grown)

Fig. 3a to 3r. Plumage and moult progression from 2W to adult.

Behaviour

The YLG spends the greater part of most days around the lake. Very occasionally it is absent for an entire day but, typically, it is present throughout the daylight hours or disappears for no more than an hour. This tendency to remain solitary around a large water-body through the day is rather characteristic of some Yellow-legged Gulls. Most inland-wintering Herring Gulls and Lesser Black-backs, for example, gather in large assemblies at or close to feeding sites such as refuse tips or at nearby loafing sites through the daylight hours, before moving in the late afternoon to form even larger gatherings at roost sites at reservoirs, lakes and gravel-pits. YLGs do certainly join feeding assemblies of large gulls at refuse tips and join traditional overnight roosts but the rather solitary daytime attachment of at least some YLGs to particular lakes was noted by R. A. Hume as long ago as the mid-1970s, when observing michahellis at Chasewater, in Staffs, (though at that time the true identity of these 'yellow-legged gulls' with dark mantle and very white head in mid-winter was not yet established) British Birds (1978) 71: 338-345.

During the periods it has been under observation, the Kingsbury bird has spent 80% of its time simply ‘loafing’. It favours a particular ‘boating pontoon’, where it rests down on its haunches and frequently sleeps with its bill and forehead tucked under its scapulars (Figure 4). In warm weather it sometimes holds its bill open, apparently using 'panting' as a cooling technique  (Figure 5; July 2013, 24^oC).

Fig. 4

Fig.5

 A second favoured resting (and observation) point is at the top of the yachting centre’s flag-pole on one of the islands (Figures 6).

Fig. 6a

Fig. 6b

More adventurous observation points include the very top of one of the electricity pylons (transmission towers) which cross the site and which are some 40 metres high (Figures 7).

Fig. 7a

Fig. 7b

It has also perched on the top of a flag-pole positioned on the apex of the tower at nearby Kingsbury church (Figures 8).

Fig. 8a

Fig. 8b. Zoomed detail from Fig. 8a.

Very occasionally, the YLG has been absent for an entire day, sometimes when there has been considerable water-borne activity (and associated disturbance) but at other times when there has been no obvious local reason. It is assumed that these absences involve feeding expeditions elsewhere. Feeding activities on site are observed only intermittently (see below). Even allowing that its absences involve feeding expeditions, it is clear that the gull is able to meet its food requirements in a relatively short space of time and is able to spend a proportionately large percentage of its time simply ‘loafing’.

Preening

As well as resting, bouts of preening are regular, sometimes lasting up to 40 minutes at a time. The images below (Figures 8) record a preening session on August 26th 2013, when the primary moult was in progress. Despite the fact that the outermost primaries were about to be replaced, they still received considerable attention. The ability of the gull to manipulate its wings, head and neck during preening is well-captured in this sequence of pictures.

Breast and underwing coverts receive first attention

Note five new inner primaries, with black subterminal band on p5. P6 to p8 have been dropped while p9 and p10 are old.

Tail, undertail coverts and flanks receive attention

Finally, the flight feathers

With preening session complete, the gull gave the 'long call'

Fig. 8a to 8i

Feeding activities

As the YLG spends such a high proportion of its time simply loafing, clearly it is able to meet its feeding requirements in a relatively short period of time. During its first year of residence, it would sometimes fly in towards the shore when human visitors to the park were feeding other birds, creating a visible feeding assembly of geese, ducks and Black-headed Gulls, but later it has shown little interest in these activities. On September 30th, 2013, it joined Black-headed Gulls following the plough in a field adjacent to the water-park (Figures 9).

Otherwise, its observed feeding activities have all involved scavenging of (apparently) already-dead fish in the centre of the lake. These are invariably fish of some size. The YLG will generally peck at the fish in mid-water, tearing of strips of flesh and such activity will continue for up to 30 minutes. On some occasions, fish are dragged to the shore (or onto the ice when the lake has been frozen), from distances of up to 200 metres across the water and taking some considerable time and effort to achieve. The images below (Figures 10) record one of these occasions, involving a 30 cm Bream, on April 1st 2011.

The Bream was initially some 200 metres from the shore. The gull was able to drag it only a few metres at a time and it took about 5 minutes for it to reach the shore.
A presumed female LBB (based on size) joined the meal and was tolerated. Generally, any competitor species was treated aggressively.
Meal complete.	Given opportunity to feed 'selectively' on land, the innards of the fish were preferred (see 10j) and scaled skin left largely intact. However, on other occasions, entire fish would be swallowed (see below).

Fig.10a to 10n.

On a second occasion, December 12th 2012, the extent to which large objects can be swallowed by gulls was well-illustrated, with the neck of the gull becoming very conspicuously distended (Figures 11).

Figures 11a to 11f

Interactions with other species

In Fig. 10k & 10L, note that a Lesser Black-backed Gull (perhaps a female on size) was allowed to feed on the fish which had been dragged to shore. Perhaps the same LBB was observed in close attendance with the YLG on earlier occasions (see below). This toleration was very much the exception however. Typically, the gull is decidedly solitary, resting alone on its favoured pontoon, even though concentrations of Black-headed Gulls and a few Lesser Black-backs are regular just a 100 metres or so away. Generally, and especially when feeding, intruders have initiated an aggressive response, involving posture and calls. The series of images below (Figures 12) show the interactions of the YLG with Crows and a Herring Gull on February 13th 2012, a cold spell when the lake was largely frozen.

Initially feeding undisturbed	As Crows approach, YLG adopts the 'Aggressive Upright-posture' (c.f. Fig B in BWP3 Herring Gull account).
Adopts 'Long Call and Throw-back' posture (see Fig. E in BWP3 HG account)	Crows remain and are joined by a 2W-type Herring Gull. YLG responds by shrouding fish with arched wings.
With Crows persisting in their attentions, the YLG lifts the entire fish and swallows it whole.
With just tip of the fish's tail protruding from bill, note how the neck and breast of the YLG are visibly distended.	Still looking distended, the YLG appears somewhat  uncomfortable. Shortly afterwards it went to water's edge and took a drink.

Figures 12a to 12h

On a few occasions during the first two-and-a-half years, the YLG did interact with (and tolerate) one or more presumed female Lesser Black-backed Gulls (Figure 10k & 10L and Figures 13) . Generally, however, it has rarely tolerated close attendance by any other species.

Fig. 13a & 13b. Yellow-legged Gull with Lesser Black-backed Gull(s)

Interactions with another Yellow-legged Gull

In late-June and early-July 2013 (before the (now) adult had returned), a 4cy Yellow-legged Gull appeared at the site and likewise spent most of the daylight hours around the lake, even perching on the same pontoon and flag-pole as used by the adult individual (Figures 14).

Fig. 14a & 14b

This individual departed in mid-July, just days before the (now) adult returned to the site. However, what was judged to be the same 4cy reappeared in mid-October. It was a smaller individual than the long-term adult and perhaps a female. On occasions it showed interest in the adult but initially it was vigorously chased away, such that it at times resorted to an adjoining lake (Hemlingford Water). On November 1st 2013 it flew to land on the water close to the adult, which responded by adopting a presumed aggressive posture (Figures 15).

Fig. 15a & 15b. Interaction of two Yellow-legged Gulls: 4cy on left and long-staying adult on right

Undeterred, the 4cy later rejoined the adult when it was loafing on its favoured pontoon (Figure 16). The adult initially ignored it but, when it decided to stand, it then chased off the 'intruder'.

Fig. 16.  4cy YLG on left and long-staying adult on right

 

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Fig. 17.  Yellow-legged Gull, July 2014, newly returned for its sixth winter and now in its seventh calendar year.
This is the first time that the gull has arrived with black lacking entirely towards the tip of the bill.

© A. R. Dean

Fig. 18.  Yellow-legged Gull, July 2016, newly returned for its eighth winter and now in its ninth calendar year.

© A. R. Dean

Fig. 19. Yellow-legged Gull, July 2017, newly returned for its ninth winter and now in its tenth calendar year.
Legs more richly yellow than at any time hitherto and bill and gape also very colourful. Effectively appearance still that of breeding season.
While 'gaping', it can be seen that red gonys spot extends just onto upper mandible.

© A. R. Dean

Fig. 20. This image was taken on January 20th, 2020, ten years to the day since the Yellow-legged Gull first appeared at KWP.
It was then in 2W plumage and in its 3cy. Here it is entering its 13th cy.

© A. R. Dean

Fig. 21. Yellow-legged Gull, July 2023, newly returned for its fifteenth successive winter and now in its sixteenth calendar year.

© A. R. Dean

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On July 15th 2024 the YLG returned yet again, for its16th season and now in its 17th calendar year