Yellow-legged Gull Larus michahellis
Regular visitor in small numbers in late summer and winter - possibly more than one phenotype involved.
Status in the West Midlands Region
The appearance of Yellow-legged Gulls Larus michahellis in Britain is now a well-established phenomenon. Yellow-legged Gull is a member of the southern group among the 'Herring Gull assemblage', and breeds in 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 the SE corner of Britain, and in rather smaller numbers further north and west, including the English West Midlands. For a full discussion of the taxonomy and identification of Yellow-legged Gull and other species or 'forms' within the group, see Yesou (2002) and Garner et al. (1997) but a brief over-view follows.
Historically, Yellow-legged Gull was considered to be a subspecies of the Herring Gull but more recent morphological and behavioural studies indicated that it should be regarded as a good species in its own right. This was further confirmed by DNA studies, which showed that michahellis is genetically differentiated from argentatus. See also comments introducing the Caspian Gull account.
Compared with Herring Gull, Yellow-legged Gull is on average more elegant, with a fuller, squarer, more flat-topped head-shape and relatively longer wings and legs. The orbital ring of Yellow-legged Gull is generally blood-red, creating a darker-eyed appearance compared with Herring Gull. The upperparts are a darker shade of grey than Herring Gull, obviously so compared with British argenteus though approached by darker examples of nominate argentatus. The wing-tip pattern displays more black and less white than Herring Gull. There is generally black on six, sometimes seven, outermost primaries. The black band across the tip of p5 is generally quite thick and unbroken, while the extent of black on the outer primaries as a whole is more extensive than on nominate argentatus. In Scandinavian argentatus there is less black on the outer primaries, often with a full white tip to p10 and no black band on p5 (but see comments below on on yellow-legged Herring Gulls from the Baltic region). The pattern of black is not, however, so distinct from that of argenteus, which also has a black band on p5, but that race has relatively pale grey upperparts so that, generally, confusion should not arise.
In adult Yellow-legged Gulls the legs are a rich yellow, though frequently less intense during the winter months and throughout the year in sub-adult birds. The yellow legs in combination with the relatively dark grey upperparts are often the features which initially attract attention on a standing bird. Note, however, that Herring Gulls sometimes display yellow-legs, particularly individuals of the nominate form from certain areas of Scandinavia and the eastern Baltic region. Individuals from the Baltic region also regularly show a black band on p5, though in most individuals this is narrow compared with michahellis. Also, there is less black in the outer primaries as a whole, with more white at the tip of p10 (sometimes a full white tip) and pale tongues on the inner webs, sometimes approaching a thayeri-pattern on p10. Thus, the pattern is more likely to simulate the wing-pattern of Caspian Gull than Yellow-legged Gull but, as there is black on the outer six primaries, an individual in which the extent of black is most well-developed could be confused with a Yellow-legged Gull. Thus, it is essential to use a full suite of characters when identifying Yellow-legged Gull. The definitive reference for yellow-legged Herring Gulls from the Baltic region is the 1998 paper by Lars Jonsson : 'Yellow-legged Gulls and yellow-legged Herring Gulls in the Baltic' (Alula 4: 74 - 100).
In winter, the head of michahellis remains relatively white and unstreaked compared with the generally well-streaked and messy head-pattern of Herring Gull, though when freshly moulted in autumn michahellis often does show limited head-streaking. This tends to take the form of rather neat streaking around the eye and across the centre of the crown, and this in itself can be quite distinctive. [Conversely, Herring Gulls can become very white-headed by mid to late December, and such individuals can look very different from surrounding Herring Gulls with well-streaked heads. There is a danger of such birds being misidentified as Yellow-legged Gulls by the incautious.]
The timing of the full post-breeding moult in michahellis is somewhat earlier than in Herring Gull, reflecting it's slightly earlier breeding season. Birds appearing in Britain in late June and early July generally show obvious signs of primary moult, with one or more central primaries 'missing' (in fact present but only part grown or just out of 'pin' and so hidden by overlapping 'inner' primaries). When preening, the state of moult and the pattern of the primary tips can often be determined.
In recent years, Yellow-legged Gulls have been arriving in Britain in increasing numbers in late summer and early autumn, as part of the species' northward post-breeding moult migration. The largest numbers are to be found in the south-east coastal counties but smaller numbers regularly reach the West Midlands Region. Intriguingly, comparable numbers are observed in the midlands during winter, whereas on the south coast the majority of Yellow-legged Gulls disperse in late autumn and few are recorded during the winter months. It is possible that individuals recorded in the midlands during winter originate from a different population from those occurring in late summer, and arguably there are phenotypic differences between 'typical' individuals observed during the two seasons.
The first fully-documented Yellow-legged Gull to be detected in the West
Midlands area was an adult at Chasewater as long ago as November 1973, though a
similar individual had been reported by A. R. M. Blake the previous year (Hume
1978). At that time, the identification and taxonomy of gulls with yellow legs
among the 'Herring Gull assemblage' were poorly understood, and, although Hume
discussed a number of forms including michahellis, the identity of the
Chasewater individual was not attributed explicitly to any particular taxon. In
the following years, observations of such individuals became
increasingly regular in southern England, and their identification features were extensively clarified. Major advances in understanding of the systematics
of the 'large white-headed gulls' also ensued, though universal agreement on
the taxonomic status of the various forms - especially which 'forms' warrant
recognition as distinct species - has yet to be achieved. Although difficult
individuals may still be encountered, and it seems likely that 'michahellis' may
itself embrace more than one phenotype, the key identification features of
michahellis gulls are now well understood. From the details published by Hume
(1978) it is now clear that the Chasewater individual was from the southern
michahellis populations and, indeed, by the late 1980s such birds were being
observed annually in the region. By the mid 1990's, 40 – 50 individuals were
being recorded annually, rising to around 75 per year by the end of the decade.
In 1999 a Yellow-legged Gull paired with a Lesser Black-backed Gull L. graellsii
and nested at Bredons Hardwick in Worcestershire. Two young were hatched in June
but did not survive.
The following analysis describes the
temporal and geographical (inter-county) distribution of Yellow-legged Gulls in
the West Midlands area and examines how these compare with the national picture.
Methods and limitations
All data published in the West Midland Bird Reports since 1973 have been extracted and examined. Records have been annual since 1986 and up to 2000 it was possible to make reasonably reliable assessments of the number of individuals reaching the region annually. Thus, detailed analysis of seasonal trends etc. is based upon the 15-year period 1986 to 2000. Thereafter numbers reached levels where determination of the numbers of individuals becomes impractical and, therefore, subsequent status trends are based upon annual maxima at well-watched sites.
The period from 1973 to 2000
of this section is reprinted, with
additions and updates, from 'The status of Yellow-legged Gull in the West
Midlands region', published in December 2004 in West Midland Bird Report
Even in this earlier period, several factors can affect the assessment and accuracy
of such numerical data and the numbers cited should be regarded as 'best
estimates' and not as absolute.
Certain issues can lead to over-estimates of numbers,
and result from duplication of published data. Adjustments (to some extent
subjective) have been applied for the two most obvious of these:
Movement between sites
Observations of Yellow-legged Gulls (and hence published figures in the WMBC Reports) are concentrated on two different types of locality. Firstly are observations at gull-roosts, which assemble in the late afternoon and evening at reservoirs and other sizeable water-bodies. Secondly are observations at daytime feeding and resting sites, such as refuse-tips and certain gravel-pit complexes. Clearly, these two sets of 'data' are not mutually exclusive. Birds feeding during the day at a refuse tip may well be seen later at a lake or reservoir roost. Hence, the published data certainly involve a degree of duplication. Examination of the published data suggests that only in Worcestershire is this likely to be a significant factor. Notable numbers of Yellow-legged Gulls have been reported regularly during the day at Throckmorton tip and similarly significant numbers in the evening at the Westwood Park roost. It is not known what proportion of birds feeding at Throckmorton later roost at Westwood but, as the two sites are only 10 miles apart as the gull flies, it is certain that interchange will occur (identifiable individual gulls of other species, e.g. Glaucous Gull L. hyperboreus, have been identified at both sites on the same day). To allow for this in the following regional and county figures, a somewhat arbitrary 'adjustment for duplication' has been made at the 50% level i.e. it has been assumed that half the numbers involved in sightings at Throckmorton are also involved in sightings at Westwood, and the 'total' figures have been adjusted accordingly.
Length of residence
It should be noted that 'totals of individuals' and 'monthly distribution of records' are numerically distinct. Individual gulls may remain in the area for more than one month and thus contribute several 'units' to the 'monthly distribution' of records. Thus, the analysis of the monthly distribution of numbers reveals the number of birds present in a given month and not birds necessarily arriving in that month nor the total number of individuals involved. Rarely are the published data precise enough to distinguish recent arrivals from individuals remaining from a previous month. To arrive at an estimate of the minimum number of individuals, monthly increments have been used. For example, if - at a given site - there were up to four birds in October and up to six birds in November, it is assumed that only two of these individuals actually arrived in November, with four remaining from October. This 'minimalist' approach will inevitably produce an under-estimate of the true numbers involved, and this may be significant at some sites. However, there is no alternative method of producing consistent, comparative data between sites and between years.
Occasionally, estimated totals of the number of birds
occurring at a given site during a calendar year have been published in the
regional Report. Such figures will often include a considerable number of individuals
observed during January. Many of these birds will have arrived, in fact, during
the later months of the previous year and are not new arrivals in the current
year. Their occurrence will have already been published in the Report for the
previous year and their contribution to the statistics incorporated into the
previous year's totals.
As a result of these factors, it should be noted that
the estimates for 'total numbers' in the following analysis will not always
accord with some of the comments in the corresponding WMBC Report for a given
The above adjustments will help to reduce inflated
figures resulting from duplicated data in the published figures.
Conversely, if there is in fact a relatively rapid
'turnover' of individuals at certain sites or in certain years, numbers taken
from the published figures may under-estimate the true situation. Most of the
published monthly figures probably relate to 'raw' day maxima (the highest
number of individuals seen on any one day during the month) rather than the
number of different individuals identified during that month. In these
circumstances, the number of different individuals may significantly exceed the
published monthly figures (see WMBC Reports for 1994 and 1995). In the absence
of structured data, no correction or adjustment can be applied for this
The final factor to take into consideration is that of
mis-identifications, which are probably seasonally biased towards the early
months of the year. This will affect observations at roosts rather than at tips
and daytime 'loafing sites'. At roosts, the light is inevitably failing, the
range of observation is usually quite distant, and certain characters such as
leg-colour are unlikely to be observed. Despite these impairments to
observation, there is evidence that the approach to identification at such
roosts is often over-simplistic. Frequently, identification appears to be based
solely on a combination of a relatively dark grey mantle and a white, unstreaked
head. While these features are a good starting point in autumn and early winter,
they are quite inadequate from late-December onwards, as by that date some
Herring Gulls L. argentatus have acquired a very white and unstreaked head. As
some Herring Gulls may also show a relatively dark grey mantle, identification
of Yellow-legged Gulls in the period from late December onwards requires this
proviso to be kept very clearly in mind. At roosts it will usually be impossible
to determine leg-colour, but confident identification will involve structure,
wing-tip pattern and the appearance of the eye, as well as mantle colour and
Even at tips and gravel pits, where the leg colour of a large white-headed gull may be among the first things to attract attention, the possibility of a Herring Gull with yellow legs has to be considered. Such birds have been claimed on a number of occasions and a certain individual was trapped and ringed at Throckmorton in December 1990. For discussion of the appearance of Herring Gulls with yellow legs, and photographs illustrating how confusing some individuals can be, see Jonsson (1998).
A further possible source of misidentification has emerged, with an apparently increasing number of hybrids. These can involve not only hybrids involving michahellis as one parent and e.g. Herring Gull as the other, but also hybrids between Herring Gull and Lesser Black-backed Gull, with the resulting offspring sometimes resembling Yellow-legged Gull. Such birds have been recorded in recent years from the Bristol area (Peter Rock in litt.).
However, although care should always be applied in identifying Yellow-legged Gulls, the influence of identification errors should not be exaggerated. As Yellow-legged Gulls are becoming more numerous visitors, occasionally misidentified individuals will, hopefully, become proportionately less and less significant and will not unduly affect the prevailing patterns of occurrence.
The analysis below must take into
limitations of the numerical data. The graphics are based upon statistics for a 15-year period and
will reveal seasonal patterns and numerical trends, but the numbers involved
should not be regarded as absolute.
Following the first record in November 1973, there were
just 18 further Yellow-legged Gulls in the following eleven years and there were
no records at all in 1985. The first record for Warwickshire came from Draycote
in June and July 1976 and the first record for the 'West Midlands County' at
Walsall in November 1984. Regionally, records were then annual from 1986,
including the first for Worcestershire, at Throckmorton, in November of that
Between 1986 and 2000, the number of Yellow-legged Gulls
visiting the region was probably between 700 (based on monthly 'increments') and
1200 (based on summated 'monthly maxima') but, allowing for 'rapid turnover'
(see 'Methods and Limitations') and over-looked non-adult gulls (see
'Age Distribution') the true figure could be significantly higher.
By the late 1990's, 70 or more
individuals were occurring annually, with up to 16 at a time at Draycote Water in
Warwickshire and up to 11 at Westwood in Worcestershire.
The annual pattern of records based upon estimated
minima (see 'Methods and Limitations') is presented in Figure 1.
Fig 1. Estimated Annual Totals of Yellow-legged Gulls in
WMBC Region, 1973 - 2000
Annual numbers rose steadily through the late 1980’s
and then remained relatively constant at around 50 individuals per year for the
first eight years of the 1990’s. A second upsurge then occurred, with around
75 individuals per year during the three years up to 2000.
An examination of the figures by county (Figure 2) shows
that, within the regional pattern, there are small but significant differences
between the four counties.
Fig. 2. Estimated Annual Totals of Yellow-legged
Gulls by County, 1986 - 2000
Numbers reached a peak in 1993 and then declined
somewhat in the ensuing four years. Numbers increased from 1998 but only by 2000
did numbers exceed the 1993 level.
Records in Worcestershire reached a plateau between 1989
and 1996, and then displayed a significant increase in the subsequent four
Numbers reported from Staffordshire
erratic but rather higher between 1988 and 1992 than between 1993 and 1997.
As in all three ‘shire’ counties, numbers increased in the three-year
period up to 2000.
In the West Midlands County, only Bartley Reservoir consistently produced records of Yellow-legged Gulls
prior to 2000 and the total number of
individuals is too low to determine trends of statistical significance. There
were marginally more records in 1995 and 1996 than in other years but the
pattern has generally been relatively constant, at around 7 individuals per
(In more recent years, the Stubbers Green area has produced more significant
numbers - see below.)
(In more recent years, the Stubbers Green area has produced more significant numbers - see below.)
The annual pattern of records for the region as a whole
is much as might be expected: a small number of records initially, during the
years when Yellow-legged Gulls established themselves as visitors to the area
(and to Britain as a whole); a fairly steady stream of observations through the
late 1980s and 1990s; and finally a second upturn in the number of records,
probably indicative of a genuine increase but also partly the result of
increasing observer awareness and effort.
The development of records in Worcestershire closely
mirrors this pattern. In Warwickshire, a polynomial trend line plotted through
the data again portrays a similar underlying trend (Figure 3). However, there is
an interesting irregularity in the pattern, with a peak in 1993 followed by a
decline in records, before a recovery in the late 1990's.
Fig. 3. Annual numbers and trend line for
This 'irregularity' reflects a significant change over
the years in the distribution of records within Warwickshire, with the Tame
Valley providing the majority of earlier records but Draycote Water the majority
of observations in more recent years.
In the ten years 1986 – 1995, the Tame Valley was the
principal area, and numbers reported there exceeded those from Draycote by a
factor of nearly two to one. In the following five years this situation was
completely reversed and numbers at Draycote exceeded those in the Tame Valley by
a factor of six to one. Changes at both locations were involved. There was a
significant increase at Draycote but also a precipitous decline in the Tame
Valley, where only three were reported in the four years 1996 – 1999. A
partial return to form occurred in 2000, when at least seven individuals were
The decline in the Tame Valley in the second half of the 1990’s may well be related to the distribution and operational practices of refuse tips in northern Warwickshire, allied to the disappearance of suitable 'loafing areas' at nearby gravel pits and kindred sites (e.g. flooding of previously 'dry' pits in the Kingsbury area, and abandonment of the fly-ash lagoons at Ladywalk following the closure of Hams Hall power-station).
(The excavation of extensive new sand and gravel pits in the Middleton, Drayton Bassett and Dosthill areas, on the Warwickshire/Staffordshire border north of Kingsbury, and an extension of landfill operations in the Dosthill/Wilnecote area produced conditions that once again attracted Yellow-legged Gulls on a regular basis from 2002 but the running down of the landfill operations in 2011 has again lead to much-reduced numbers of LWHGs in the middle Tame Valley.)
Annual numbers reported in Staffordshire
between 1986 and 2000 varied
somewhat erratically. The majority of records through the period as a whole came from the three large reservoir roosts, at Belvide, Blithfield and
Chasewater. Very few were recorded at any of these sites in 1993, 1996 and 1997.
As with the other ‘shire’ counties, numbers increased in the three
years 1998 –2000, with Belvide in particular reporting higher numbers than
hitherto. A key change between the early and later years of the period was
the decline in latter years of reports from Westport Lake, near Stoke. Reports
were annual between 1986 and 1993, with around six individuals each year. Since
1994, however, there have been relatively few reports and none at all in 1994,
1999 and 2000. This reflects a general decline in reports from Westport of gulls
of all species, which may to some extent reflect changes in observer activity.
Figure 4 shows the monthly distribution of records of
Yellow-legged Gulls in the region between 1986 and 2000. The data are plotted
from summer through winter (rather than January to December) to match the
natural profile of arrivals and departures. Each column shows the summated
totals for that month ('the number of birds present') and also the estimated
total of arrivals in that month, calculated as described in 'Methods and
Fig. 4. Monthly distribution of Yellow-legged
Gulls in WMBC region,
1986 – 2000, plotted from summer through winter
The corresponding monthly distributions for the
individual counties are shown in Figure 5 (note the different 'Numbers' scale in
Fig. 5. Monthly distribution of Yellow-legged
Gulls by county, 1986 – 2000
The monthly profile of numbers across the region as a
whole (Figure 4) shows a bi-modal pattern, with an initial summer influx in
July, a slight decline in numbers through the autumn, and then a second and more
substantial peak during the winter months between October and January. Examining
the monthly distribution by county, however, reveals a wide disparity between
the four counties in the proportion of summer records (Figure 5). The regional
profile - with a small but distinct summer peak followed by a more pronounced
winter peak - is reflected closely in the records from Worcestershire and the
West Midlands County. In Warwickshire, numbers in summer have been
significantly higher as a proportion of the total, with July the single most
productive month. In Staffordshire, by contrast, there have been very few
reports between July and September, with records almost exclusively during the
Data on the age of Yellow-legged Gulls in the region is
available for about 75 percent of records. Since 1994, many of the records
published in the WMBC Reports have been tabulated, facilitating ready reference
to numbers but unfortunately losing data on the age of the individuals involved.
Many observers do not actively search for non-adult
Yellow-legged Gulls, particularly first and second-year individuals, so the
proportion of non-adults recorded will certainly be less than the true number
occurring. The early arrivals in June and July might be expected to consist
largely of adults but the true age-distribution later in the winter remains to
be fully clarified. Nevertheless, of the records published with age-data, 68
percent were adults. Of the 32 percent non-adults, 4% were first-years (1W/1S),
8% second-years, 11% third-years, and 9% fourth-years.
Comparisons with other areas
The largest concentrations of Yellow-legged Gulls in the
UK are to be found in the south-east coastal counties, between Essex and
At Pagham Harbour in Sussex, for example, over 300 may occur at a time during
July and August (per Richard Fairbank and the Sussex Ornithological Society)
while over 300 have been recorded at a single site in Dorset during September
(per Shaun Robson and the Dorset Bird Club). Over 380 were at East Tilbury in
Essex during September 2001 (per Howard Vaughan, Paul Wood and the Essex
In these south-east coastal counties, there is a large
influx between July and September, with numbers peaking in August or early
September. Numbers then decline during the autumn. There is no evidence of a
second influx of 'wintering' birds and, indeed, relative to the numbers present
in late summer, there is an almost complete exodus during the winter months.
This mirrors the situation in northern continental
Europe, where numbers also peak in August and early September, and decrease
after October (Jonsson, op. cit.).
Figure 6 shows the monthly profile of numbers during
1986 – 2000 in Sussex, based on ‘monthly maxima’ extracted from the Sussex
Bird Report by Richard Fairbank, and ‘estimated arrivals’ calculated by the
author as per ‘Methods and Limitations’.
Fig. 6. Comparative monthly distribution of
Yellow-legged Gulls in Sussex,
1986 – 2000,
Just 40 miles inland, numbers in the vice-county of
Surrey are much lower and more comparable with those in the West Midlands (data
per Jeffery Wheatley and the Surrey Bird Club). Numbers increase rapidly through
July, peak in August and then decline slowly through the autumn and winter
months. Apart from a slight increase in the total number recorded during
January, there is little evidence of a 'bi-modal' distribution. Winter records
are regular but totals during 1994 to 2000 never exceeded 60% of the July/August
peak and could well involve birds remaining from the summer.
The number of Yellow-legged Gulls congregating on the
south coast of England is very large compared with the West Midlands. Over 300
individuals may be present at one time in Essex , Sussex and Dorset during the
peak months of August and September. In comparison, numbers at any one
time in the West Midlands region rarely exceed 20 to 30 individuals during the
winter peak in December. It may be dangerous to jump to conclusions about
differences in the seasonal distribution between southern England and central
England when the total 'populations' are of such different magnitudes. However,
the increasing numbers in winter in the West Midlands, and the fact that numbers
reach a peak at that season, is very much at odds with the pattern in the
English heartlands for Yellow-legged Gulls on the south coast and also in
northern continental Europe.
How does the pattern in the West Midlands region compare
with adjoining midlands counties?
During 1997, Jon Baker carried out detailed observations
of Yellow-legged Gulls at Dix Pit in Oxfordshire (Baker, 1998). Numbers in the
early months of the year were low, with none from late April through May. The
first returning birds were in early June, followed by ‘a small passage of
birds for the rest of June and July’. There were seven birds on July 21st and
August 1st, after which ‘the species became scarce again’. Numbers then
increased significantly through October , reached a day maximum of 26 on
November 26th , and declined only slightly during December. Thus, the seasonal
pattern at this site in Oxfordshire mirrors that for the West Midlands region.
In Derbyshire, the pattern also matches that in the West
Midlands area. 'The first birds are usually noted in June and July followed by a
big influx in August. Numbers then drop off slightly in September and October
before rising again to a peak in December. Slightly lower numbers are noted in
January with numbers then falling away until the last birds are noted in April'
In Northamptonshire, annual numbers have increased since
1995 and reached around 100 in 2001 (per Mike Alibone and the Northamptonshire
Bird Club). 'There is one clear peak emerging, in August/September. Birds begin
to arrive in July and are evident until October. There are a few winter records
but there is no discernible second peak.' Thus, the seasonal pattern in
Northamptonshire does not mirror that for the West Midlands region and is closer
to that evident in southern England.
There are disconcerting differences between the apparent
seasonal patterns in various midland counties.
Within the West Midlands region, there is a significant
winter peak in Staffordshire, Worcestershire and the West Midlands County. In
Warwickshire, although there are significant numbers in winter, July has been
the single most productive month.
In a study at an Oxfordshire site and also in
Derbyshire, peak numbers are again during the winter but in Northamptonshire
numbers peak in August/September and there is no recorded winter influx.
Such differences are highly unexpected in contiguous
The winter peak evident in a majority of midland
counties is also at variance with the seasonal profile of Yellow-legged Gulls in
their 'heartland' areas on the south coast.
A high proportion of summer records in Warwickshire
comes from the Tame Valley and involves 'daytime' observations at 'resting'
sites such as the gravel workings at Dosthill and, in earlier years, the fly-ash
lagoons at Hams Hall Power Station. By comparison, records from Draycote much
more often involve roosting birds and, significantly, are more concentrated in
the winter period, September to March.
In Staffordshire, a very high proportion of records come
from the gull roosts at the three major reservoirs, Belvide, Blithfield and
Chasewater, and, in this county, records have been almost exclusively in winter.
Observations at gull-roosts are much less frequent
during the summer, before the winter influx of the majority of gulls of other
species attracts observers' attention.
How genuine is the very different pattern in the West
Midlands area compared with the south coast? Are the differences in seasonal
patterns between counties in central England substantive? Is the bi-modal
distribution and a winter peak perhaps an artefact, arising primarily from the
on-set of concentrated 'winter roost watching' in late autumn?
The observations of Baker in Oxfordshire (op. cit.)
encompassed all months of the year and can be assumed to be real and free from
In order to test for seasonal bias in the West Midlands
regional data, I have analysed subsets of data from sites where there has
been at least a degree of year-round observation at the appropriate time of day,
and over a period of several years.
Two such subsets of data from the West Midlands region
have been used. Firstly, records from Throckmorton, which is the only site for
which the published data regularly encompassed most months of the year and was
available throughout the period 1986 –2000. To provide a second, independent
'control set', I have observed Yellow-legged Gulls on a year-round basis at
Bartley and Frankley Reservoirs during the four years 1999 – 2002 (and thus
slightly outside the principal period of analysis). Numbers of Yellow-legged
Gulls at this site are very small but the site has the advantage (in this
context) that there is both a diurnal 'loafing' area and an over-night roost,
and as a consequence Yellow-legged Gulls frequent the site in both the summer
and winter months.
The monthly distributions resulting from these two
subsets of data are presented in Figure 7.
Fig. 7. Monthly distribution of Yellow-legged
Gulls at two sites with year-round observations
The results from each site are very similar. 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
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.
This pattern is echoed in data from Derbyshire and
Oxfordshire but not in Northamptonshire. The apparently disjointed distribution
of wintering birds within adjoining midland counties is highly unexpected
but analysis of selected 'year-round' subsets of data re-affirms the bi-modal
pattern and a winter peak in numbers across most of the West Midlands area.
Where do the late arriving wintering birds come from?
The simplest explanation is that they are birds that arrived in summer in
southern England or continental Europe as part of the principal pre-moult
migration and then subsequently relocated within (or to) Britain as part of a
secondary post-moult migration.
The seasonal pattern on the south coast of England, and
in northern continental Europe, shows that most of the Yellow-legged Gulls
moving north in late summer disperse during the winter. Clearly, given the large
numbers involved, most must return south at this time. However, perhaps a small
number instead moves north and west into the more land-locked areas of Britain,
to areas where reservoirs and refuse tips attract such large numbers of Herring
Gulls and Lesser Black-backed Gulls at this season.
A more intriguing explanation is that they involve a
second and relatively small influx from southern Europe, perhaps from another
part of the species' breeding range. At least a proportion of the individuals
found in England in winter appear to average smaller, darker and rounder-headed than is typical
for Yellow-legged Gulls originating from the Mediterranean basin. Such
characteristics have been associated with Yellow-legged Gulls from the Atlantic
seaboard of southern Europe and NW Africa (Martin Garner and Dick Newell in
If a second population is involved, 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 period since 2000.
Since 2000, the number of Yellow-legged Gulls visiting the region has reached levels where only summarised data are published in the regional Reports and detailed analysis is no longer possible. Generally, the species is now recorded in all months but the broad picture of a bi-modal pattern of occurrence (late-summer and winter influxes, respectively) is firmly established. It is likely that the number of individuals annually is now well into three figures.
In 2004, a count of 18 on August 31st at Chasewater (Staffs) constituted a regional record at that time for a single locality. During 2007, a new regional locality-high of 20 occurred at Draycote (Warks) on January 23rd, while at least 22 individuals were identified there during the last week of the month. In 2010, a new record was established at Draycote, with 25 on July 28th and 26 on July 30th. At least 36 individuals were identified on these two dates, comprising 14 adults, one fourth-year, 7 second-years and 14 juveniles. In Worcestershire, 16 were counted at Throckmorton landfill in October 2009. In the West Midlands 'county', 14 were at Stubbers Green on July 21st 2010, with at least 31 different individuals during the month.
The five-yearly mean maximum counts from selected sites during 2001 - 2010 are presented in Table 1.
|5-year Mean||Draycote||Tame Valley||Throckmorton||Westwood||Belvide||Blithfield||Chasewater||Bartley||Stubbers Green|
|2001 - 2005||9||3||8||7||2||8||4|
|2006 - 2010||19||6||9||6||9||4||8||8||8|
Table 1. Five-yearly mean maximum counts of Yellow-legged Gulls at selected sites in the West Midlands Region, 2001 - 2010.
It is considered 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 day/site counts, as presented in the Table.
See also a selection of images in the Photo Gallery, to illustrate the appearance of Yellow-legged Gulls and to facilitate considerations of origins and phenotypic variation. The item Studies of an individual Yellow-legged Gull also includes a series of images showing the progression of a single individual from 2W (3cy) to adult plumages.
Following the first fully-documented record in 1973, Yellow-legged Gull
has become a regular visitor to the West Midlands region and has been annual
since 1986. By the late 1990s, records numbered 75 or more individuals annually
and by 2010 annual totals were in three figures. Up to 26 have
been present at a time at Draycote (Warwickshire) and up to 18 at Chasewater
(Staffordshire). Nearly 70% of birds identified have been adults, though a
proportion of immatures, particularly first and second years, is probably
over-looked. A detailed analysis of data from 1986 to 2000 indicates 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 watched
principally 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 larger 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 at key sites for Yellow-legged Gulls on the south coast of England and
also in northern continental Europe. In these areas, where relatively large
numbers arrive in the summer, there is a major exodus during the mid-winter
months. The winter influx in parts of the Midlands involves very small numbers
compared with the peak populations found on the south coast and perhaps a small
proportion of individuals departing from southern England 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.
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 article is based. 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). David Emley clarified specific points in respect of
Staffordshire. Martin Garner and Dick Newell provided valuable comments on
current debate and speculation regarding the appearance, variations and possible
origins of Yellow-legged Gulls observed in England during the winter.
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