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 Yellow-legged Gull Larus michahellis

 Yellow-legged Gull photo index
Yellow-legged Gull Photo Index

Regular visitor in late summer and winter, in small to moderate numbers.

For historical perspective see analysis for the period up to 2015.

Yellow-legged Gull Larus michahellis is now a well-established and increasingly numerous visitor to Britain. It may be seen in all months but, nationally, the largest concentrations occur in late-summer. It has also bred or attempted to breed in England on a few occasions. In its report for 2010 the Rare Breeding Birds Panel (RBBP) noted a typical annual total of one breeding pair and two or three mixed pairs with Herring Gull or Lesser Black-backed Gull. By 2018, the RBBP noted a slight decrease in breeding statistics, with a downturn of 33% based upon 15 years of data. Its wider breeding range includes the Mediterranean basin, west to the Atlantic seaboard, and east to the southern Black Sea. After breeding it undertakes a moult migration to the north, bringing it in some numbers to western Europe and southern Britain during July and August. The largest assemblies are on the south coast and may involve up to 200 individuals at the most favoured sites. Smaller numbers are found regularly further north, including the West Midlands, but the species becomes scarcer north and west of a line from the Humber to the Mersey. Yellow-legged Gull is a member of the southern group among the 'Herring Gull assemblage' and, together with Caspian Gull, is now accorded species status. Range expansion from eastern Europe has brought the ranges of Caspian Gull, Herring Gull and Yellow-legged Gull into contact (see map in Litwiniak et al. 2021). Although mating is predominantly assortative, there are increasing cases of hybridization in mixed colonies. Hybrids of known provenance (confirmed by ringing) have been recorded in various areas of Britain, again including the West Midlands. Hybrids most frequently involve Caspian x Herring Gull but, disconcertingly, there are instances of known hybrids between between Caspian Gull and Herring Gull having an appearance very similar indeed to Yellow-legged Gull, including the primary pattern (Neubauer et al. 2020). Occasional Herring Gulls with yellow legs provide another pitfall (see Jonsson 1998 and Neubauer et al. 2010).Caspian Gull has also hybridised with Lesser Black-backed Gull (see Litwiniak et al. 2021) while hybrids between Lesser Black-backed Gull and Herring Gull can resemble Yellow-legged Gull (such birds have been detected in the Bristol area - Peter Rock in litt.). The numbers of Yellow-legged Gulls now reaching the West Midlands mean that the occasional hybrid or yellow-legged Herring Gull will not affect the perceived overall status but an appropriately careful approach to identification of Yellow-legged Gulls and Caspian Gulls remains appropriate.

Status in the West Midlands Region

The historical pattern

The history and status of Yellow-legged Gull in the West Midlands up to 2000 was summarised by Dean (2004, West Midland Bird Report 69: 234-249). An edited version with updates to 2015 is on this site <here>). In 2000 the number of records annually was still small enough for individual records to be identified and a full annual, monthly, age and geographical analysis was presented. The summary of conclusions was as follows:

'Following the first record in 1973, Yellow-legged Gull has become a regular visitor to the West Midlands region and has been annual since 1986. Records now number 75 or more individuals annually and up to 16 have been present at a time at Draycote (Warwickshire) and up to 11 at Westwood (Worcestershire). About 70% of birds identified have been adults, though a proportion of immatures, particularly first and second years, is probably over-looked. There are some notable differences between the four counties in the annual and monthly distributions of records. Although natural patterns of movement in the counties may differ to some extent, it is also likely that patterns are influenced by  (a) sudden changes in habitats at key sites which make them either more or less attractive to gulls, and  (b) the relative extent to which observations are focussed on roosts, which are principally watched in winter. The latter factor, in particular, could influence the apparent seasonal patterns of arrivals and departures. However, published observations as a whole and analysis of carefully chosen subsets of data both suggest arrivals in two phases: a summer influx around July, associated with the species' northerly post-breeding moult migration from the Mediterranean basin, and a winter influx between October and January. Such a bi-modal pattern and a relatively significant influx in winter are at odds with the profile of numbers in the key sites for Yellow-legged Gulls on the south coast of England. In these areas, where relatively large numbers arrive in the summer, there is an almost complete exodus during the mid-winter months. The winter influx in the West Midlands involves very small numbers compared with the peak populations found on the south coast, and may perhaps indicate that a small proportion of individuals departing from the south undertakes a secondary post-moult migration further north and west rather than returning immediately to southern Europe. A more intriguing possibility is that such winter arrivals involve gulls from another part of the species' range in southern Europe, perhaps including the Atlantic seaboard. Such gulls may perhaps favour different sites from those arriving from the Mediterranean basin, and this could go some way to explaining the uneven distribution of Yellow-legged Gulls across the midlands during the winter.'  

The overall region-wide profile based upon all records combined - with a small but distinct summer peak followed by a more pronounced winter peak - was reflected closely in the records from Worcestershire and the West Midlands County while in Staffs the winter peak was even more dominant.  In contrast, numbers in Warwickshire in late summer were significantly higher as a proportion of the total, with July the single most productive month. Studies at an Oxfordshire site (Baker 1998) and in Derbyshire (Keys 2002) also found peak numbers during the winter but in Northamptonshire numbers peaked in August/September and there was no recorded winter influx (per Mike Alibone and the Northants Bird Club). Such differences are  unexpected in contiguous inland counties and remain to be explained.

The recent pattern.

Based upon the period 2015 to 2019, an updated 5-year analysis follows, including comparisons with the earlier analyses. The numbers of Yellow-legged Gulls have increased significantly since 2000, particularly in the late-summer influx and notably at Draycote. It is likely that, region-wide, the number of individuals annually is now well into three figures while Draycote has produced a much-enhanced regional maximum of 48 (in 2013 and 2019). The regional totals during July and August now exceed those recorded in winter, though Draycote contributes significantly to this situation.  With such higher numbers visiting the region, detailed analysis based upon individual records is no longer possible. Only summarised data are now published in the regional Reports. Such tabulated data facilitates concise documentation of seasonal distribution but means that data on age distribution, for example, is no longer available. There is also an inevitable increase in duplication of data, with individual gulls moving between sites (an obvious example being gulls recorded during the day at a feeding site such as landfill and then logged subsequently at a roost). Conversely, it is likely that there is significant 'turn over' of Yellow-legged Gulls visiting the region and that, during the course of a year, the number of individual Yellow-legged Gulls visiting the region may well be two or three times the maximum site counts, as presented in published tabulations.

Such caveats notwithstanding, Figure 1 shows the the current regional monthly distribution of Yellow-legged Gulls, based upon summed monthly maximum counts from all sites tabulated in the five WMBC Annual Reports covering 2015 to 2019.

Yellow-legged Gull: monthly distribution in West Midlands

Figure 1. Monthly distribution of Yellow-legged Gulls in the West Midlands region, 2015 - 2019.

The region-wide distribution now shows significant numbers in all months between July and February, with smaller numbers in the remaining four months, embracing the spring and early summer. While August is the single most-productive month, there is a less-evident bi-modal trend than in the pre-2000 period, with a range of only 24% spanning the eight months July to February. However, as in the earlier analysis, there are significant variations between the four 'counties' and between individual sites, which become masked when their data are combined in a region-wide profile as portrayed in Figure 1. Figure 2 shows two portrayals of the monthly distributions within the four individual counties. Note that the left block of four uses a common numbers scale, with a max of 140 for each county, thus providing a direct comparison of numbers in the four counties (with higher numbers county-wide in Staffs and Warks than in Worcs and WMids). In the right block of four, the numbers axis is scaled to the maximum value for each individual county (thus expanded axes for the smaller peak values in Worcs and WMids). This facilitates a visual comparison of seasonal patterns.

Yellow-legged Gull: monthly distribution in four West Midlands counties

Figure 2.  Monthly distribution of Yellow-legged Gulls by county, 2015 - 2019.
(a): same number scale (140 on Y-axis), for direct visual comparison of numbers.    (b): number scale matched to county peaks, for clearer seasonal comparison.

In Warks, there is a marked peak during July and August, the traditional period for the species to arrive in Britain as a result of its post-breeding moult migration. In the remaining three counties, the distribution is skewed much more towards the later autumn and winter months, progressively so for Worcs, Staffs and WMids, respectively. The distinct July / August peak in Warks is a product entirely of the large number at that time which are to be found at Draycote. This single site is one of only four contributing data to the Warks totals and dominates the county's monthly profile. It contributes 85% to the overall 5-year total for Warks and 94% to the July / August total. It also contributes 27% to the regional four-county total in Figure 1, to which over 40 sites contributed tabulated data, and nearly 50% to the regional July / August total . The numbers now occurring at Draycote during July and August are responsible for the relatively 'flat-topped' distribution between July and February in Figure 1. When Draycote data are excluded from the regional profile, the distribution for all other sites combined shows a peak between October and February. Thus, while there are differences in detail from the pre-2000 distribution, there remains the distinction of a winter peak across most of the region but a late-summer peak in Warks, though the latter is attributable entirely to the significant July / August numbers at Draycote.

Yellow-legged Gull: monthly distribution in West Midlands

It would seem that Draycote is now a direct destination for a meaningful number of Yellow-legged Gulls undertaking their post-breeding moult migration. This may in part involve a redistribution of gulls previously occupying locations on the south coast, where certain previously favoured sites have witnessed a radical decline in numbers since the early 2000s, assumed to result from closure of local landfill sites (e.g. in Sussex and Dorset; see Stanley (2020) for details of changing patterns in Dorset). Draycote provides a suitable roosting site, is close to still-active landfills and hence offers an attractive destination. Most of these late-summer arrivals move on from Draycote during September, mirroring the traditional pattern on the south coast, but, regionally, significant numbers are still to be found at Draycote in winter. While much lower than the peak numbers there in late-summer, these numbers are still comparable with those at other individual sites in the region (though significantly lower than winter numbers at all other sites combined). Draycote is, in fact, among the top three sites for numbers during both the late summer and the winter months (Table 1).

Table 1. Summed maximum counts during (a) July/August and (b) October to February
at the three top-ranked sites in each period.

At Draycote, the summed maxima for July / August constitute nearly twice the total for the winter period (October to February). At Belvide and Chasewater, both in Staffs, the ratios are just 0.07 and 0.11, respectively. However, at Blithfield, also in Staffs, the ratio is in-between at 0.79. It is hard to escape the conclusion that the seasonal profiles away from Draycote are affected to some degree by 'observer habits' and roost duration. For example, several of the traditional key roosts in the region certainly receive more attention during the winter than the summer. Some roosts disperse completely after wintering-visiting gulls leave for their breeding grounds and do not reform until the autumn, thus later than the July / August peak for incoming Yellow-legged Gulls. As part of the pre-2000 analysis, an examination for seasonal bias was conducted by exploring the data from just two sites, considered at that period to provide reasonably reliable year-round data : the landfill site at Throckmorton (then operating at full intensity) and the reservoir at Bartley. This found that, at these two sites:

'There is a more-even balance between summer and winter numbers compared with data from the region as a whole but the bi-modal distribution and winter peak are still evident. It can be concluded that 'seasonal bias', resulting from the on-set of  'winter gull-roost watching', does inflate the relative prominence of the winter peak in numbers but is not wholly responsible for the bi-modal pattern in the monthly distribution. Hence, there is evidence that the winter peak in numbers in the West Midlands area is genuine. Rather than a single peak of birds in summer, as on the south coast, it would seem that there is a summer influx, a brief hiatus, and then a second influx of winter visitors.'

The origins of the Yellow-legged Gulls arriving in winter remains to be clarified. Despite much-reduced numbers in some south coast counties, the simplest explanation is still that later arriving Yellow-legged Gulls in the midlands  involve gulls which arrived earlier on the south coast and have then undertaken a secondary movement to, by then, well-formed winter gull-roosts in the midlands. However, compared with the typical late-summer arrivals, some of the winter arrivals appear to be (on average) smaller, darker mantled and even-more-inclined to show a 'gleaming white' head. Size and dark mantles have led to speculation that they may originate from a different part of the range, perhaps including the Atlantic coast of Iberia, though the very white-headed appearance may count against this. Without meaningful ringing or GPS data, the origins of winter arrivals cannot be determined with any certainty. There may well be no simple, single origin. Gulls from various parts of the range may well be involved.  Although just a single individual, it is worth noting that a typical Mediterranean-style Yellow-legged Gull appeared (as a 2W) at Kingsbury Water Park during a cold snap in January 2010. It has returned every year since (as at 2022), arriving consistently in the first half of July and remaining through the central winter period before departing in late-January or early February. It is fully documented <here>. This individual, at least, arrives in the West Midlands region during the 'classic' late-summer period and settles in for six or seven months.

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Principal thanks go to the small but enthusiastic group of gull-watchers in the West Midlands region who have produced the data upon which this and the earlier analyses are based. Also the county recorders and their teams who have diligently documented regional records in the WMBC Annual Reports, edited by Dave Emley. I am very grateful to the following for providing comparative data or publications on Yellow-legged Gull for their respective areas: Mike Alibone (Northamptonshire Bird Club), Richard Fairbank (Sussex Ornithological Society), David Hawkins (Oxford Ornithological Society), Rodney Keys (Derbyshire Ornithological Society), Shaun Robson (Dorset Bird Club), Howard Vaughan and Paul Wood (Essex Birdwatching Society), and Jeffery Wheatley (Surrey Bird Club). Dick Newell and the late Martin Garner provided valuable comments on the debate and speculation regarding the appearance, variations and possible origins of Yellow-legged Gulls observed in England during the winter.  

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