Scandinavian Herring Gulls wintering in Britain
Coulson, J. C., Monaghan, P., Butterfield, J. E. L.,
Duncan, N., Ensor, K., Shedden, C. and Thomas, C.
Ornis Scand. 15: 79-88.
Biometric information was obtained from 13000 Herring
Gulls Larus argentatus caught and ringed in
northern England and southern Scotland outside the
breeding season between 1978 and 1983. Morphological
differences between males and females and between
British and Scandinavian Herring Gulls have been used
to identify both the sex and race of the birds. We
describe the wintering distribution of the
Scandinavian birds in Britain, their age and sex
ratios and their time of arrival in and departure from
Britain. Scandinavian Herring Gulls start to arrive in
Britain in small numbers in September. The proportion
of Scandinavian birds increases to a peak in December-
January and the birds depart abruptly in late January
or early February. Very few Scandinavian Gulls
penetrate to the west side of Britain, while on the
east side there is considerable regional variation in
the proportion of Scandinavian birds. Between 70% and
80% of the adult Scandinavian birds examined were
female. The proportion of adults amongst Scandinavian
birds was much higher than amongst British birds.
J. C. Coulson, J. E. L. Butterfield, N. Duncan, C.
Thomas, Dept of Zoology, Univ. of Durham, South Road,
Durham DHI 3LE, UK.
P. Monaghan, K. Ensor, C. Shedden, Dept of Zoology,
Univ. of Glasgow, Glasgow G12 8QQ, Scotland, UK.
Bird species which breed over a wide climatic range
often show geographical variation in their migratory
behaviour; individuals breeding in the more hospitable
parts of the species range are sedentary, while those
subject to rigorous climatic conditions overwinter far
from the breeding grounds. The Herring Gull Larus
argentatus is such a species. The British birds
are largely resident, in that there is no general
shift of the population from the British Isles during
the winter months and, while seasonal movements within
Britain do take place (Coulson et al. 1982),
movements over 300 km are rare (Thomson 1925, Poulding
1954, Harris 1964, Parsons and Duncan 1978). The
Herring Gulls breeding in the northern region of
Norway and the Murmansk region of USSR, on the other
hand, undertake comparatively long distance winter
migrations. Moreover, ringing studies have
demonstrated that the northern Norway population
mainly overwinters in areas to the south of those
frequented by more southerly breeding Norwegian birds
(Olsson 1958, Monaghan, unpubl.). The milder, maritime
climate of Britain provides suitable overwintering
conditions for these northern breeding birds and the
indigenous British Herring Gull population is joined
in winter by numbers of Herring Gulls which breed in
the most northern areas of Europe. Most studies of the
behaviour and ecology of the Herring Gull have
concentrated on its breeding biology and comparatively
little is known of the period outside the breeding
season. The ringing studies mentioned above have
tended to concentrate upon the post-breeding movements
of Herring Gulls from a particular colony or area, as
indicated by the recoveries of dead birds. The origin
of the Herring Gulls wintering in a particular place,
and the interactions of birds from different breeding
areas have been little studied. There are
morphological differences between British and
Scandinavian breeding Herring Gulls which have
warranted their division into separate sub-species.
The nominate L. a. argentatus, the larger and
darker of the two, breeds in Scandinavia and NW Russia
while L. argentatus argenteus breeds further
south including Britain (Barth 1964, 1966, 1967, 1968,
1975a, 1975b, Monaghan et al. 1983). We have
used these morphological differences to identify the
L. a. argentatus component of the wintering
Herring Gulls in northern Britain and, using a large
sample of individually marked birds, have made a study
of the mixed populations. This paper reports on the
identification of birds of Scandinavian and NW Russian
origin and describes their distribution, age
structure, sex-ratio and timing of arrival in and
departure from northern Britain.
2.1. Sampling Herring Gulls
The main study area was a large part of northern
England and southern Scotland (shaded area in Fig. 1).
The study was made in the five winters between 1978
and 1983. Samples of Herring Gulls were captured by
cannon-nets at feeding sites, usually at refuse
disposal tips. The average catch exceeded a hundred
Herring Gulls and throughout the five years of this
study over 15000 Herring Gulls were captured. More
than 13000, caught outside the breeding season, were
weighed and measured. All of the birds were ringed
using B.T.O. numbered metal rings, and over 9000 were
given a unique combination of colour-rings, allowing
them to be identified as individuals in the field.
Reservations -that catching exclusively at refuse tips
might produce a biased sample were dispelled by the
mobility of the birds and the fact that marked
individuals fed not only at refuse tips but also at
many other locations inland, on the coast and at sea.
Work in progress demonstrates that, on average, tips
are used on less than two days in each week by
individual birds. Throughout this paper we refer to
"Scandinavian" birds since this region covers the area
from which we have had foreign recoveries in the
breeding season (Fig. 1), although it is very likely
that some birds from NW Russia are also involved (see
Fig. 1. The location of all foreign breeding season
sightings and recoveries of Herring Gulls ringed
during the winter months in the main study area in
Britain (shaded). Small dots represent single birds,
large dots represent five birds.
The following measurements were taken from each bird.
(a) Wing length. This was taken by the standard method
involving the maximum length to the nearest mm after
straightening the primaries.
(b) Bill depth. This was measured to the nearest 0.1
mm at the gonys with the beak held closed.
(c) Bill length. This was taken from the base of the
culmen to the tip of the bill. However, this was found
to be an unreliable measurement with a low level of
reproducibility by different persons. In 1979, this
measurement was replaced by head and bill length.
(d) Head and bill length. This is the length, measured
to the nearest mm, from the back of the cranium to the
tip of the bill. The method and its use in sexing
birds has been reported by Coulson et al.
(1983b). While head and bill length was found to be
the most accurate measure of sex in a single
population, this is not the case when populations are
mixed (see Method 1, Sect 2.3). Head and bill length
does, however, give the highest correlation with wing
length of any of the measurements taken (r=0.76,
n=743). It has, therefore, been used as a substitute
for wing length in birds which were missing the
longest primaries (either through moult or damage),
using the relationship: estimated wing length=239.25 +
1.56(head and bill length).
(e) Weight. Each bird was weighed either on a direct
reading balance to the nearest g or on a spring
balance to the nearest 10g.
(f) Plumage. Several aspects of the wing tip pattern
were recorded (see Coulson et al. 1982). In
particular, the presence or absence of the thayeri
pattern on the 9th primary (see Barth 1968) was
recorded. This pattern is characterised by the grey
area on the hind margin of the 9th primary extending,
uninterrupted by black pigment, into the white
"mirror" at the end of the feather. It has been
recorded once only from the British population but
occurs in up to 27% of the Herring Gulls breeding in
northern Scandinavia (Barth 1968). Examination of 59
skins of Herring Gulls from NW Russia in the
Zoological Museums of Lenningrad and Moscow
Universities confirms that these birds also have a
high proportion of individuals (27%) showing the
thayeri character. This therefore gives a further
character by which the area of origin of some
individual birds caught in Britain could be determined
and we used these as part of the sample of
"Scandinavian" birds in the discrimination analysis.
(g) Leg colour. We examined the leg colour of all
Herring Gulls captured. There has recently been a
series of records of 'yellow-legged' Herring Gulls in
Britain and in the southern part of the North Sea
(Grant 1983, Devillers 1983). We found no Herring
Gulls with yellow legs throughout the study. Thus we
were not involved with Herring Gulls from the east
Baltic or those from southern France and Iberia.
(h) Mantle shade. During the first year of the study,
we became aware of the darker grey on the mantle of
Herring Gulls which possessed the thayeri wing pattern
and also in those which were larger than British
breeding birds (including a Norwegian ringed adult).
Since 1980, we have used a 13 shade reference strip
covering the range of grey found on the mantle of
Herring Gulls we captured. This offered a greater
series of intermediate shades than that in commercial
colour and shade charts (e.g. Munsell charts). The
shades were produced by exposing matt photographic
paper for progressively longer periods and developing
the papers until no further change took place. The
shades were numbered 1-13 (dark to light) and
corresponded (approximately linearly) to the Munsell
range N4.5 to N7.5. Our Munsell values for northern
Scandinavian Herring Gulls agreed closely with those
obtained by Barth (1966) using a reflectometer. We
found higher (that is paler) shades than he did for
British birds, but his results came from a very small
sample of British birds taken in the extreme north of
the country. The distributions of mantle shades for
birds with the thayeri wing tip pattern and for birds
caught in Britain and subsequently seen or recovered
in northern Scandinavia are shown in Fig. 2. These
distributions are similar but the figure also presents
the shade distribution of British breeding birds and
it is evident that there is very little overlap
between these and Scandinavian birds.
(i) Ageing. All birds were aged by plumage into four
immature year classes and an unaged, adult class (see
Witherby et al. (1945) and Grant (1982) for
details). We employed the convention that the immature
age classes changed on 1 July each year.
2.3. Separation of British and Scandinavian Herring
Gulls using body measurements
Two different methods were used to separate Herring
Gulls according to their sex and race. Both made use
of the SPSS discrimination analysis programme
DISCRIMINANT (Nie et al. 1975).
Fig. 2. The percentage distribution of the shade of
the grey mantle of Herring Gulls on an arbitrary scale
of 1-13 covering the Munsell range N4.5 to N7.5.
Adults: (a) from British breeding colonies. (b) ringed
in Britain during the winter months and subsequently
found in breeding colonies in north Norway. (c) which
possess the thayeri wing pattern characteristic of
Scandinavian birds (see text). Note the high degree of
separation between British and Scandinavian birds
which makes this morphometric feature a good indicator
of race in this species.
This method makes use of two measures of body size and
each bird is assigned to one of four categories:
British male, British female, Scandinavian male and
Scandinavian female. The most appropriate body
measurements were selected on the basis of a
comparison between samples of adult Herring Gulls from
breeding colonies in north Norway (Barth 1967 and C.
Johnson, unpubl. Ph.D. thesis) and northern Britain
which had been sexed by dissection. Bill depth was
found to be the best method of sexing live individuals
from mixed populations of British and Scandinavian
birds since it differed least between the two races
and had a high degree of separation between the sexes.
Bill depth increases with age so, for birds of four
years or less, the bill depth measurement was
corrected to that expected when it becomes a seven
year old adult, using the relationship between bill
depth and age reported by Coulson et al.
The races were separated using wing length but when
the longest primaries were in moult or not fully
grown, wing length was estimated from the head and
bill measurement as described above.
When we first developed Method 1, we expected that it
would separate correctly about 95% of the birds.
However, despite correcting bill depth for age, the
degree of overlap between the biometrics of birds from
the two populations was greater than we had envisaged.
In fact the accuracy of the method, measured by
testing it on an independent sample of 220 birds from
the British breeding population revealed that 40 (18%)
of the birds were mis-identified. Clearly, the origin
of all individual birds could not be identified with
confidence using this method. However, after a
correction was applied for this error, Method 1 still
allowed us to obtain realistic estimates of the
proportion of Scandinavian Herring Gulls in our
catches. This was done in the following way. Samples
with less than 18% of the birds classified as
Scandinavian were considered to be composed entirely
of British birds; catches with greater than 18% of
birds classified as Scandinavian had the proportion
corrected using the relationship:
y = 1.563x - 28.13
where y is the corrected percentage of Scandinavian
birds and x is percentage obtained by Method 1. This
relationship corrected catches with up to 50%
Scandinavian birds in them and none of our catches
exceeded this level. The correction allows for an 18%
error in the identification of both British and
Scandinavian birds. At 50% of each the errors cancel
each other out.
Examination of the independent sample of 220 Herring
Gulls known to belong to the British breeding
population, and for which measurements of both head
and bill and wing length were available, revealed that
the error increased to 30% when head and bill length
was used to estimate wing length. The October catches,
when many birds lacked the longest primary and where
wing length has been estimated using head and bill
length, have been corrected for this 30% error.
This method makes use of the mantle shade of the birds
over two years old, in addition to the body size
measurements, to predict whether or not the bird
belongs to the British or Scandinavian race. Since
there is a high degree of separation of the two races
using mantle shade (Fig. 2), we were able to classify
correctly all of the individuals in the sample of 220
Herring Gulls from the British population and in the
samples used in the discriminant analysis 98% were
Application of both Method 1 and 2 to the same samples
gave very similar estimates of the proportion of
Scandinavian birds thus validating the way in which
the Method 1 estimates were corrected. Method 1 was
used on all first and second year birds throughout the
study(since they lack extensive grey mantle plumage),
and on birds aged over two years in 1978 and 1979,
before mantle shade was recorded. From 1980 Method 2
was used on all samples of birds over two years old.
The proportions of wintering Herring Gulls of
Scandinavian origin were estimated for three age
groups (lst year, 2-4 years old and adult) in the
eastern and western halves of the study area. The main
catching localities are shown in Fig. 3.
Fig. 3. The proportion of adult Herring Gulls caught
between November and January at different localities
in Britain which were identified as Scandinavian
(black sectors). Note that very few Scandinavian birds
penetrate to the west side of Britain and on the east
side there is considerable regional variation. Small
circles represent samples of between 30 and 99 adult
birds: large circles represent samples greater than
99. The sample sizes at each site are given in the
3.1. Area of origin of the Scandinavian Herring Gulls
Breeding season sightings and ringing recoveries of
Scandinavian Herring Gulls marked during this study
are shown in Fig. 1. The great majority of these
foreign sightings and recoveries were within the
Arctic Circle, with none outside Norway. These results
are consistent with our finding that a high proportion
of the wintering Scandinavian Herring Gulls in east
Britain have the thayeri wing pattern (Tab. 1, last
line). Several of the recovery sites shown in Fig. 1
are within 100 km of the Russian border and
Tatarinkova (1970) has shown that some Herring Gulls
ringed in NW Russia overwinter in eastern Britain. It
is therefore very likely that some of the birds which
we identified as Scandinavian breed in NW Russia,
particularly since these birds also have a high
proportion with the thayeri wing pattern. However, we
have not received any recoveries or sightings from
3.2. Geographical distribution of Scandinavian Herring
Gulls within the study area
Tab. 1. The timing of capture in eastern Britain of Herring Gulls known to breed in Scandinavia (A)
and with the thayeri wing pattern (B) compared with that of the birds we have identified as
Aug Sep Oct Nov Dec Jan Feb
A. No. of marked birds seen or recovered in
Scandinavia during the breeding season O 1 1 10 7 18 2
B. No. of thayeri individuals caught O 1 (4)** 42 50 59 26
C.* Total no. of known Scandinavian birds caught 0 2 5 50 55 71 27
D. Total no. of adults caught 206 676 408 755 720 1365 483
E. Total no. of adults identified as Scandinavian
(from Tab. 3) 0 5 (41) 164 196 344 100
% known Scandinavian (C. 100/D) 0 0.3 1.2 6.6 7.6 5.2 5.6
% Scandinavian with thayeri pattern (B. 100/E)- - 20 (10) 26 26 17 26
* 9 birds where the thayeri wing pattern had been noted were later seen in Scandinavia so line C=A+B-9.
** Figures for October are given in brackets since primary moult at this time prevents identification of
wing pattern in a number of birds.
The proportion of adult Scandinavian birds captured in
the three months, November, December and January in
each of the four winters of the study at the main
sites in NE England are shown in Tab. 2. There is no
significant difference between winters and we have
combined data from all years when considering the
geographical distribution and timing of arrival of the
Scandinavian birds. Tab. 3 shows the proportion of
adult Scandinavian Herring Gulls in catches made in
the eastern and western halves of the study area in
each month between August and April. It is evident
that few adult Scandinavian birds penetrate to the
west side of Britain and Fig. 3 shows this clearly in
the November to January period. This finding is also
supported by the presence of only one adult with a
thayeri wing pattern among more than 3000 adults
caught outside the breeding season on the west side of
Britain. The situation on the east side contrasts
markedly with this; on occasion, over 10% of the adult
Herring Gulls in catches had the thayeri wing pattern.
Fig. 3 also shows the variation in proportions which
occurs in eastern Britain. One area, encompassing Tyne
and Wear, Co. Durham and Cleveland has a high
proportion of Scandinavian Herring Gulls. Based on an
estimate of 15000 adult Herring Gulls wintering in
this area, there are some 3600 Scandinavian adults
present each winter. On the other hand, there is a
much lower proportion of adult Scandinavian Herring
Gulls overwintering in eastern Scotland and the
Scarborough area of Yorkshire (Fig. 3). A summary of
the catches at each site, showing the samples sizes,
is given in the Appendix.
Tab. 2. The proportion of adult Herring Gulls caught at the main
study sites m NE England during November, December and January in
each winter which were of Scandinavian origin.
Winter Sample No. of Percentage
size Scandinavian Scandinavian
1978-1979 393 116 29.5
1979-1980 622 201 32 3
1980-1981 432 134 31 0
1981-1982 447 146 32.7
The proportion of Scandinavian Herring Gulls among the
2-4yr old birds (Tab. 4) and the first years (Tab. 5)
were also higher in the east coast catches but the
levels are much lower than those for adults.
Tab. 3. The proportion of adult Herring Gulls caught in east and west Britain, outside the breeding
season, which were identified as Scandinavian. Data have been pooled for the four years of the
East Britain West Britain
n No. of % n No. of %
Scandinavian Scandinavian Scandinavian Scandinavian
Aug .................... 206 0 0.0 46 0 0.0
Sep .................... 676 5 0.7 103 0 0.0
Oct .................... 408 (41) (10.0) 430 0 0.0
Nov .................... 755 164 21.7 480 2 0.4
Dec .................... 720 196 27.2 325 5 1.5
Jan .................... 1365 344 25.2 736 3 0.4
Feb .................... 483 100 20.7 177 1 0.6
Mar .................... 10 2 20.0 357 0 0.0
Apr .................... 1 0 0.0 381 0 0.0
Figures for October are given in brackets since, due to the absence of a wing length measurement for
Herring Gulls caught at this time in primary feather moult, these figures are likely to be less
Tab. 4. The proportion of 2-4yr old Herring Gulls caught in east and west Britain, outside the breeding
season, which were identified as Scandinavian. Data have been pooled for the four years of the study.
East Britain West Britain
n No. of % n No. of %
Scandinavian Scandinavian Scandinavian Scandinavian
Aug .................... 81 0 0.0 35 0 0.0
Sep .................... 226 0 0.0 46 0 0.0
Oct .................... 296 (14) (4.7) 146 0 0.0
Nov .................... 169 20 11.8 145 2 1.4
Dec .................... 172 28 16.3 119 4 3.4
Jan .................... 366 58 15.8 111 2 1.8
Feb .................... 226 14 6.2 86 0 0.0
Mar .................... 37 0 0.0 97 0 0.0
Apr .................... - - - 148 0 0.0
Figures for October are given in brackets since, due to the absence of a wing length measurement
for Herring Gulls caught at this time in primary feather moult, these figures are likely to be
3.3. Timing of arrival and departure of Scandinavian
Herring Gulls in northern Britain
The period of arrival of Scandinavian Herring Gulls in
Britain is protracted. Examination of the proportions
of adult Scandinavian Herring Gulls caught in
different months suggests that they begin to arrive in
small numbers as early as September (confirmed by a
ringing recovery). The proportion of Scandinavian
adults increases over the next three months, reaching
a peak in December when they form 27% of the adult
catch (Tab. 3) and 18% of the total catch. The
Scandinavian first year birds found in August and
September have probably been misidentified (because of
the magnitude of the correction required to convert
the bill depth to adult dimensions) as there are no
other indications that first year Scandinavian birds
arrive before October (Olsson 1958, Tatarinkova 1970).
If these early records are accepted as errors, the
first year Scandinavian Herring Gulls appear to arrive
later than the adults, with no birds recorded in
October and only four (2% of the Scandinavian birds
caught) in November. The proportion of first years
amongst the Scandinavians increases to 10% in December
but declines in January and none were caught in
February (Tab. 6) or March. The 2yr old birds appear
to arrive and depart at the same time as the adults.
We have not caught any Scandinavian Herring Gulls
during the summer but there is some evidence from both
Russian (Tatarinkova 1970) and Norwegian ringing that
a few immature birds may summer in Britain.
The protracted pattern of arrival of Scandinavian
Herring Gulls is confirmed by the captures of birds
with a thayeri wing pattern and birds which were
marked on capture and were later seen or recovered in
Scandinavia during the breeding season (Tab. 1). The
timing of capture of these birds also shows that they
do not arrive in Britain in large numbers until
November. The proportion of the identified
Scandinavian adults which had a thayeri wing pattern
remained approximately constant at about 22% between
September and February (Tab. 1). This proportion of
thayeri adults is similar to the values of 21-27%
reported by Barth (1968) for northern Norway and to
our own finding of 27% thayeri among birds taken in NW
Russia. The dates of sightings in Britain of Herring
Gulls known to breed in Norway are shown in Tab. 7.
Since the timing of capture will influence the
distribution of sightings in the same winter, these
results relate only to winters subsequent to that in
which the bird was first marked. A similar pattern to
that reported above emerges; the majority of
Scandinavian Herring Gulls do not arrive in Britain
until late autumn and maximum numbers are present in
January. Most of the birds which have been breeding
in north Norway leave Britain in late January and
February (Tab. 7) and by March there are no
Scandinavian birds remaining in the study area. Our
field observations suggest that the departure in
February is abrupt with most of the birds departing
within 3 or 4 days.
Tab. 5. The proportion of 1yr Herring Gulls caught in east and west Britain, outside the
breeding season, which were identified as Scandinavian. Data have been pooled for the
four years of the study.
East Britain West Britain
n No. of % n No. of %
Scandinavian Scandinavian Scandinavian Scandinavian
Aug..................... 38 1 2.6 65 1 1.5
Sep..................... 162 2 1.2 174 3 1.7
Oct..................... 597 0 0.0 258 1 0.3
Nov..................... 242 4 1.7 227 1 0.4
Dec..................... 221 24 10.9 105 1 1.0
Jan..................... 213 29 13.6 106 1 0.9
Feb..................... 181 0 0.0 113 2 1.8
Mar..................... 59 0 0.0 106 1 0.9
Apr ..................... - - - 101 0 0.0
Tab. 6. The age composition of the Herring Gulls identified as British (Brit.) and Scandinavian
(Scan.) for catches in NE England during the non-breeding season. Data have been pooled for the four
years of the study. Differences between British and Scandinavian Herring Gulls in age composition are
significant for all months (P < 0.01 in all cases). Figures in brackets are percentages of the
total for each race. (There are insufficient Scandinavian birds in September for a meaningful
Sep Oct Nov Dec Jan Feb Totals
Brit. Scan. Brit. Scan. Brit. Scan. Brit. Scan. Brit. Scan. Brit. Scan. Brit. Scan.
No. adult...... 671 5 367 41 591 164 524 196 1021 344 383 100 3557 850
(64) (71) (30) (75) (60) (87) (61) (79) (68) (80) (50) (88) (55) (81)
No. 2-4 yr old..226 0 272 14 149 20 144 28 308 58 212 14 1311 134
(21) (0) (22) (25) (15) (11) (17) (11) (20) (13) (27) (12) (20) (13)
No. 1 yr old... 160 2 597 0 238 4 197 24 184 29 181 0 1557 59
(15) (29) (48) (25) (2) (22) (10) (12) (7) (23) (24) (5.6)
X2 - 69.4 57.2 30.4 24.7 62.4
3.4. Sex ratio of Scandinavian Herring Gulls
In a sample of 178 adult Herring Gulls showing the
thayeri wing tip pattern, 146 (82%) were identified as
females from their biometrics. Similarly, of 213 adult
birds with a mantle shade of less than 6 on our scale
(the range in which there is little likelihood of
British birds being included). 71% were female.
Clearly, there is a marked inequality in the sex-ratio
of adult Scandinavian Herring Gulls wintering in NE
Britain. The mean wing length of the 178 thayeri birds
was 441 mm which is similar to the mean wing-length of
Scandinavian birds recorded in the London area by
Stanley et al. (1981). Presumably their
sample was also biased in favour of females.
3.5. Age composition of Scandinavian Herring Gulls
Tab. 6 gives the age structure of the Scandinavian and
British Herring Gulls caught in NE Britain each month.
Overall a much higher proportion (81%) of the
Scandinavian birds was adult, compared to British
birds (55%), with higher proportions of adults
occurring among the Scandinavian birds in all months
that they were present in appreciable numbers.
Tab. 7. The timing of sightings in Britain in the years subsequent to capture
of 20 individually marked Herring Gulls known to breed in north Norway. The
first line gives the total number of sightings of these birds within the study
area in each month. The patterns of first and last sightings of each bird in
each winter are given in lines 2 and 3, respectively. Taking the first sighting
to indicate arrival and the last departure, line 4 shows the number of these
birds remaining in the study area in each month.
Aug Sep Oct Nov Dec Jan Feb Mar
Total sightings 0 4 12 38 38 74 29 0
First sightings 0 2 8 10 8 8 1 0
Last sightings 0 0 0 3 6 15 13 0
No. remaining 0 2 10 20 25 27 13 0
3.6. Field identification of Larus a.
argentatus and L. argentatus argenteus
Recently, considerable interest has built up in the
possibility of identifying the area of origin of
Herring Gulls visiting Britain using field
observations (Hume 1978). Since we have had many birds
which were examined in the hand, measured for mantle
shade and size and then subsequently seen in the
field, we are in a position to comment on the
identification of northern Scandinavian birds under
Firstly, the lighting conditions vary the extent to
which isolated individuals appear to have a light or
dark mantle and without other birds for comparison, we
would place very little confidence on such
identifications. In fact we note that Morley (1979)
did not detect the shade difference in north Norwegian
Herring Gulls which she caught at the breeding sites,
nor did Stanley et al. (1981) note the darker
shade, presumably because of the lack of British birds
for comparison. Even when British Herring Gulls were
available for comparison, we found it difficult and
often impossible to identify northern Scandinavian
Herring Gulls in the field on days with bright winter
sunshine. The task was somewhat easier with total
cloud cover, when the amount of incoming light was
reduced. Further we warn against the apparent change
in shade arising from the position of the bird in
relation to the observer; on several occasions
apparently dark plumaged birds became light. It is not
usually possible to recognise the thayeri wing pattern
in the field. In general, the northern Scandinavian
birds show less black pigment on the wing tips and
almost invariably have a long white tip to the 10th
(outer) primary which can be noted if the wing is
opened, for example, during an aggressive encounter.
Note, however, that an appreciable minority of British
birds, particularly those from NE Scotland, also show
this character. The shortage of Scandinavian males
wintering in NE England also means that size is of use
in only a minority of cases. In our view, a very large
Herring Gull with dark grey wings and mantle and with
reduced black pigment and more extensive white
markings on the wing tip is almost certainly a bird
from Scandinavia or NW Russia. In the majority of
cases, however, the identification can only be
satisfactorily made with the bird in the hand and with
suitable reference shades available for comparison.
Ringing studies have shown that the continental
Herring Gulls which visit northern Britain during the
winter months originate mainly in arctic Norway and NW
Russia (Olsson 1958, Tatarinkova 1970, present study).
We have found that the Scandinavian birds which reach
Britain winter almost exclusively on the eastern side
of the country where, in places, they form about 30%
of the wintering Herring Gulls. The failure of the
Scandinavian birds to penetrate in any numbers to the
western coast of Britain is surprising, considering
the distance they have travelled to reach Britain in
the first place. We have evidence (unpubl.) that
British Herring Gulls are equally unwilling to move E
to W across England and Scotland and that narrow
stretches of land (less than 120 km in places) act as
a considerable barrier. Scandinavian birds concentrate
in certain areas within our study area in eastern
Britain. For example, higher proportions of these
birds have been found in NE England between the River
Tyne and the north of Yorkshire, than in areas to the
north or south. This may arise from the small numbers
of resident breeding birds in this area which,
presumably, dilute the proportion of the Scandinavian
Herring Gulls elsewhere. Alternatively, the local
birds may have a competitive advantage and force the
Scandinavian birds into areas where the density of
other Herring Gulls is relatively low. Stanley et
al. (1981) reported the exclusive use of areas in
SE England by Scandinavian Herring Gulls but we have
found no such examples in northern Britain, indeed the
Scandinavian birds were always in the minority.
The arrival of the Scandinavian gulls in our study
area is spread over a 5-month period, September to
January, but few birds arrive before mid October. The
peak of arrivals in the November-early January period
is late compared with the arrival of other gull
species from Scandinavia (Radford 1960,1962, Coulson
et al. 1984). Thus most of the adults arrive
after primary moult is almost complete, but the moult
is unlikely to be the cause of the late arrival since
the first year birds, which do not moult, and older
immature birds, which moult earlier (Walters 1978,
Coulson et al. 1983a), arrive at the same
time as the adults. The late arrival of the
Scandinavian birds contrasts with the earlier arrival
of the British breeding birds, many of which are
departing from NE England for their breeding areas as
the Scandinavian birds are arriving. This will be
discussed further in another paper.
Most of the Scandinavian birds depart during January
and in the first half of February. The exit in
February is synchronised and most of the birds depart
in the same 3 or 4 days. A similar abrupt departure
also occurs in the Norwegian Great Black-backed Gulls
which winter in NE England (Coulson et al.
1984). Some sighting and ringing recoveries of adult
Herring Gulls in northern Norway suggest that these
abrupt departures involve a rapid and probably direct
movement back to the breeding area. Our observations
were based predominantly on females and we have
insufficient data to determine if, on average, males
depart at a different time to females. It would be
interesting to know whether Scandinavian birds, in
particular those wintering on the continental coast of
the North Sea, depart at the same time.
Throughout the winter period, the proportion of adult
and immature Scandinavian Herring Gulls differs
markedly from the proportion in the British samples.
It is possible that the low proportion of immature
Scandinavian birds stems from these young birds moving
shorter distances from their natal areas. This is not
supported by either the Norwegian or the Russian
ringing recoveries (Tatarinkova 1979). An alternative
possibility, that the breeding success in northern
Scandinavia is lower than that in Britain, is more
likely. There is support for this latter explanation
in that there are reports of low breeding success in
Norway (Folkestad 1978, Johansen 1978) and this is
probably the situation in northern Scandinavia as a
whole. A similar low proportion of immature birds has
been found among Norwegian Great Black-backed Gulls
wintering in NE England has also been attributed to
poor breeding success (Coulson et al. 1984).
The differences in size and colour of the Scandinavian
Herring Gulls as compared with British birds are in
marked contrast to the situation in the Great Black-
backed Gull where British birds are the same size (and
shade) as those breeding in northern Scandinavia and
NW Russia (Coulson et al. 1984). The reason
for the appreciable difference in size of the Herring
Gulls is not clear although the size change follows
Bergmann's Rule with greater size occurring in the
colder part of the animal's range. This suggests that
the selection for size in this species takes place in
the spring and summer when the populations are
separated. If this explanation which has been put
forward in general terms by Salomonsen (1955) is
correct, then it would appear that the selection
pressures on size in the Great Black-backed gull
occurs in the wintering area and it is, perhaps,
significant that many Great Black-backed Gulls move
from Scandinavia to Britain at least two months
earlier and remain there longer than the Herring
Appendix. The numbers and proportions of Scandinavian birds amongst
adult Herring Gulls caught at different localities in Britain during the months
of November, December and January (1978-1983). These data are shown in Fig. 2.
Location County Number Number %
Caught Scandinavian Scandinavian
Scarborough North Yorkshire 208 15 7.2
Mickleby North Yorkshire 65 20 0.8
Loftus Cleveland 40 8 20.0
Darlington Durham 68 6 8.8
Hartlepool Cleveland 240 34 14.2
Wingate Durham 547 188 34.4
Coxhoe Durham 943 272 28.8
Chester-le-Street Durham 242 74 30.6
Consett Durham 149 48 32.2
Greenside Tyne and Wear 32 9 28.1
Prudhoe Northumberland 83 25 30.1
Hexham Northumberland 50 3 6.0
Kirkcaldy Fife 265 28 40.6
Aberdeen Grampian 113 4 3.5
Inverness Highland 86 0 0.0
Lochgilphead Strathclyde 68 0 0.0
Helensburgh Strathclyde 229 2 0.9
Croy Strathclyde 75 1 1.3
Bishopbriggs Strathclyde 556 2 0 4
East Kilbride Strathclyde 206 1 0.5
Irvine Strathclyde 49 0 0.0
Longtown Cumbria 42 1 2.4
Walney Cumbria 318 0 0.0
Lancaster Lancashire 37 0 0.0
Acknowledgements - The data used in this paper
were collected with the help of a number of
individuals from Durham and Glasgow Universities and
we extend our thanks to them all. We wish to thank
Christine Johnson (nee Morley) for supplying us with
standard body measurements of sexed Herring Gulls
collected in north Norway. We also wish to acknowledge
the assistance given by Dr. R. Furness, N. Aebischer,
S. Greig, K. Bayes, H. Wright, D. Hutchinson, J.
Richardson, E. Henderson and M. Bone. Thanks are also
due to staff of the Nature Conservancy Council, Royal
Society for the Protection of Birds and Scarborough
Council for their co-operation and assistance which
enabled us to obtain biometric data from birds taken
in breeding colony culls. This research would not have
been possible without the continued goodwill and
facilities provided by the executives and staff of a
number of local authorities, in particular, Durham
County Council and Strathclyde Regional Council. The
study was financed by research grants from the Natural
Environment Research Council.
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