Herring Gull argentatus
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DISCUSSION
PAGE: PLEASE MAIL AND ADD COMMENTS
Immature
LBBGs resembling fuscus in Western Europe (so-called discusfus LBBG's)
Every
spring
and early summer, LBBG showing arrested and suspended primary moult can be observed in the Netherlands, Belgium and northern France.
It’s believed these LBBG belong to the race intermedius or otherwise
resemble the race graellsii, except perhaps 2cy LBBG with second
generation primaries in spring. In articles dealing with the eastern
nominate race fuscus [Jonsson,
Birding World 1998, Rauste, Limicola 1999] this feature (among others) was
mentioned as common in fuscus and very rare or non-existing in intermedius and graellsii.
Therefore it seemed to be an easy clue in the field to find fuscus in Western
Europe.
However,
annually about 50 of such birds (LBBG with arrested or suspended
moult) have
been observed and probably arrested moult occurs in about 3-10% of 3cy LBBG. In all
cases these immature LBBG resemble intermedius and graellsii, not fuscus.
Several colour and metal ringed 3cy confirm that these birds indeed are intermedius
and graellsii, from Scandinavia, the Netherlands and Britain.
For
decades it's known that darkness of upper-parts or general appearance of fuscus
and intermedius overlap. Now
it seems that arrested moult is only uncommon (but not extremely
rare) in intermedius, and one may wonder what make the difference between intermedius
and fuscus in 3cy.
The question remains (or is back): “How to recognize
LBBG of the
race fuscus in Western Europe?”. Fuscus 2cy in
spring probably hold best chances. But identification of juvenile, 3cy, 4cy and
adult fuscus seem to be extremely tricky and may be impossible when birds are not ringed.
On
this page we like to enlarge upon characteristics which (when combined) point towards fuscus, but may be seen
in intermedius and graellsii as well
(as stand-alone feature or accumulated characteristics in a single bird).
-
A
slight warning: we will mention graellsii, intermedius or fuscus,
but note that all identifications of birds
(unless ringed) are tentative, so please interpret use of a racial name
(xxx) as
meaning "appears to be closest to xxx based upon population averages".
If you feel some may be closer related to other taxa, please let us know.
-
Note
also that judging grey tones might be very difficult. Much depends on your
screen, our interpretation of grey-tone in the field and finding that tone back
in the picture before publishing, etc. etc. It has all been said, but may be
good to be repeated.
-
Another
note: it’s meant to be a discussion page. Those observations are what we (and
other gull-watchers) recently came across
and we might well be wrong on points. Please let us know what you
think. If it’s true what’s said below, we may not be able to recognize
immature fuscus (unless ringed) in Western Europe in spring.
-
Last
note: this page deals with immatures in spring, not with adults in autumn.
What
features can be used best to establish age accurately? This question not only
applies to intermedius and fuscus but to all gull species. Is it
bare part coloration or
generation of primaries and secondaries? As photographs of ringed birds show,
2cy fuscus
may return from the wintering grounds with very advanced upper-parts and with
complete 2nd generation primaries, almost resembling older (sub)adult fuscus in
spring (Limicola 13, p159 plate 35 and this
link for examples of very advanced moult). In
these cases, bare part coloration points to at least 3cy (with much yellow on
the bill, sometimes even red on the gonydeal angle and pale yellow legs). When
all the primaries are moulted in spring before departing north and are therefore
of a successive generation, 2cy fuscus
may very much look like 3cy birds.
The
same problem may arise for advanced 3cy, which resemble 4cy, as can be seen in
this LBBG intermedius,
a probable 3cy from Dannes, France, May 05 2001. It looks
like 4cy, but the primaries suggest 3cy (no white tips and no mirror on P10).
But in many respects the very advanced upper-parts, white tail and bare part coloration
resemble 4cy. Compare this bird with the 4cy bird in front (click
thumbnail), which shows white spots on the primaries and a white mirror on P10. Bare parts clearly advocate at least 4cy.
Such (advanced 2nd summer?) LBBGs can probably be found in every large group of intermedius
in spring in Western Europe.
This
is another 3cy LBBG Dutch intergrade
in the Maasvlakte colony, May 27 2003, Maasvlakte, the Netherlands. Fortunately,
primary moult was arrested at P8, so the outer primaries can be judged second
generation. But imagine 3cy birds which do succeed in complete replacemnet of
the primaries. Such birds would be very difficult to age accurately.
But
there are more problems. Some immature LBBGs may have all black primaries with an obvious white
mirror at P10. Others show very small, hardly visible white tips on the outer
primaries and no mirror on P10. How to estimate their age accurately?
To
summarize: fuscus may return in summer in very advanced plumage and they
may clearly differ from same aged intermedius/graellsii. But they do not
differ much from one year older graellsii/intermedius and to distinguish
between 2cy fuscus and 3cy intermedius may be very difficult, when fuscus
returns with complete replaced remiges. Furthermore, 3cy intermedius and
3cy Dutch intergrades may appear very adult-like, just like 3cy fuscus.
On average, fuscus is a small gull, smallest of
the LBBG-complex with short legs and long, elongated wings (the hand of fuscus
may be as long as nominate argentatus (!): 450 mm.). Of course, females
are smaller than males, females have a more friendly facial expression and the
overlap between male fuscus and female intermedius has been
mentioned in several articles. The fact that size is far from diagnostic is
shown by the left individual, which has exactly the size of present Common (Mew) Gulls,
Larus canus.
This very
small (female?)
individual has the primaries jet-black, shows no white tips and just an
extremely small faint mirror on P10 is visible (see the problem of ageing above). Grey-tone
is too pale to fit fuscus and is in line with intermedius. Again
moult in the upper-parts is advanced. The bare parts are very adult-like: the legs
are lemon yellow, the red spot is confined to the lower mandible and there is only a small black spot
on the upper mandible. This is one of the smallest birds seen in spring 2001.
It's not only fuscus showing long
wings, as the next
picture shows: an adult intermedius,
June 17 2001, Maasvlakte, the Netherlands. Note the long primary projection,
which apparently may also be present in intermedius. This LBBG shows a
cold grey-brown hue on the upper-parts, common in intermedius when
feathers become old. Nevertheless, the brown cast is not as characteristic as
in abraded adult fuscus, which get a mahogany ('intense brown', 'warm
brown') hue (contrary intermedius which get 'milky brown', 'grey brown' hue).
For comments on brown coloration, see adult
fuscus page.
The
on average short
legs (especially the tibia) are not a very reliable feature to distinguish
between fuscus and intermedius, on individual level.
The
bill in fuscus is said to be different from intermedius, but
probably it's the difference between fuscus and graellsii what is
meant. The difference between the bills of average fuscus and graellsii
from the U.K. is quite obvious. But like fuscus, intermedius
and probably to a lesser extend also some Dutch intergrade LBBGs may show a parallel
slender bill, sometimes a bit droopy, as the image shows. This is
a female, ringed at the
Maasvlakte, the Netherlands July 10 1995, now in her 6th summer. Note,
besides the bill, the
brown (but not mahogany) hue on the upper-parts. It seems bill-height and
relative bill length may overlap in individuals and differ only on average on population level.
Normally,
2cy fuscus returns on the breeding grounds with plain,
dark, fresh or slightly abraded second and third generation scapulars and second
generation wing coverts, while some
fuscus show
fresh third
generation all black coverts in between (BW 11-8, p304 fig 1 and fig 2; 2cy
fuscus section). In 3cy fuscus,
some individuals already show complete adult-like upper-parts (Limicola 13, p163 plate
42) but in quite some birds, the outer-half of the greater coverts, the
outermost median and lesser coverts and some of the tertials show immature brown
feathers. However, 2cy fuscus may return with barred or anchor patterned
second generation feathers as well, resembling graellsii (Limicola 13,
p159 plates 37 & 38; BW 11-9, p 305 fig 3).
Intermedius
is variable in second generation scapular pattern. Some may show very dark
second
generation feathers, black-centred and slightly paler at the edge and tip. In
some spring 2cy birds, these plain feathers are very worn and bleached dirty
brown, but
clearly must have been plain, lacking obvious barring and anchor pattern (see
also next paragraph). Left is a picture of a 2cy
LBBG, July 06 2001, IJmuiden, the Netherlands. It shows very plain patterned new coverts and
scapulars. The centres are black and towards the fringes, the feathers become
more brown-grey. Third generation feathers (often found in the median
coverts, inner greater coverts and the scapulars) can be present in graellsii/intermedius
as early as May and will show abrasion by mid-summer (as in fuscus).
 And
here are pictures of a 2cy LBBG, July
07 2001, IJmuiden and a 2cy
LBBG, June 18 2002, Maasvlakte, the Netherlands.
Probably these are intermedius and show advanced moult for 2cy LBBG. The outer greater and lesser coverts (carpal edge) are
still juvenile, but all other visible feathers are replaced by at least second generation
feathers, of which many are old and abraded. The tertials are second
generation. In the scapulars, a few third generation adult-like feathers have
been replaced recently. Primary moult is in line with 2cy intermedius and
graellsii. Apparently, very dark, blackish
fresh scapulars or coverts and advanced moult in the upper-parts may be seen in intermedius
as well.
 Very
dark intermedius may frequent LBBG-colonies as south as the
Maasvlakte,
the Netherlands (see map). Here, they establish mixed couples with paler Dutch
intergrades. This sub(?)-adult summer was
photographed June 17 2001. Note the brand new primaries in spring; it's hard to believe
these are half a year of age already. Do some intermedius moult the
primaries in late winter and early spring, prior to northbound migration? Intermedius from Scandinavia may be as dark as
fuscus, as stated by Jonsson "... It is not possible to rely on this
feature alone for sub specific identification". [BW 1998, p297 plate 4]. He
found about 15% overlap in blackness (click also on the illustration). Of
course he refers to adult LBBG, but it seems reasonable to believe an immature offspring
of such intermedius might get as dark as an offspring of similar dark fuscus,
although Jonsson (in BW 1998, p 307 figure 8) mentions the presence of
"pitch black scapulars" in fuscus, as a feature to distinguish fuscus
from intermedius. Warm brown hue on old coverts (mahogany hue) is
mentioned to be common in fuscus. However, intermedius with old coverts
can show strong brown hue on old coverts as well, as is demonstrated by this
ringed Norwegian intermedius,
September 22 2002, Le Portel, France.
Fuscus
has the wintering grounds very far south (sub-Sahara Africa, see ring
recoveries section) and this might give
reason to moult upper-parts in a much higher pace than West European LBBG,
which often winter north of Mauritania, Morocco and recently in (S)W
Europe. For long, the main strand of thought was that graellsii
and intermedius
do not moult mantle and scapulars before departure to the wintering grounds. In
fact they do; they sometimes even moult some coverts as early as August in the breeding colony (see the
juvenile sections). On the wintering grounds, many intermedius
replace the upper-parts and wing-coverts, just as many fuscus do. Subsequently, intermedius may return in spring with
slightly worn second generation scapulars and coverts. They may even grow third generation dark plain feathers by May, as this
LBBG from Le Portel (France), May 04 2001 shows. It's a 2cy LBBG with already
a few third generation dark grey scapulars and moulting the median coverts.
The
average West European LBBG has most wing-coverts juvenile in spring. But quite some graellsii
and intermedius show advanced moult with all visible coverts included in
the moult on the wintering grounds. Here is an
example of a (presumed) graellsii, Etaples (France), May 05 (!!!) 2001: the
tertials are all second generation and the upper three show much abrasion.
Probably, these tertials were moulted already some time ago. The entire tail
has been replaced by second generation rectrices. Many wing coverts are second generation.
For
graellsii and
intermedius, this is probably the most advanced moult stage possibly in spring (by early May) in
2cy. Early May, P4 may be shed.
Here
is another 2cy from May 11 2001, the Netherlands. It shows
second generation
scapulars randomly. The last moulted scapulars are third generation-like:
plain dark grey with an obvious darker (black) centre / shaft.
Right
is an example of 2cy LBBG (May 11 2001, the Netherlands) with complete
second
generation body plumage. The tail was recently moulted; the white fringes are
obvious. In the scapulars, the last moulted feathers are plain grey with a dark,
almost black triangular centre. These examples from early May indicate what
intermedius and graellsii may look like in June and July, when feathers start to
get older, bleached and worn. Two examples are shown below.
This
2cy has abraded second generation upper-parts, which have to be
moulted in the winter quarters and shows a new tail. Such 1st summer fall in
type
3, see 2cy May,
with a simple pattern on all the 2nd generation upper-parts: plain brown-grey
with a pronounced shaft-streak. (Photographed June 17 2001, Naaktstrand
Maasvlakte, the Netherlands.)
 Here
are other abraded 2cy, June 18 2002
(left) & June 17 2001
(right),
Maasvlakte, the Netherlands.
Some 2cy LBBG grow very dark plain grey median coverts and lower scapulars,
which were moulted early in the winter and are already abraded when they return in
spring.
Apparently,
immature intermedius can show much variation regarding moult, abrasion and pattern on
second
and third generation scapulars and wing-coverts. In this, they may resemble fuscus to a
high degree. The presence of third generation scapulars as early as May is rare,
but nevertheless occurs in intermedius. And, what makes things problematic,
they may be plain dark.
One
of the most striking and easy clues to find immature fuscus in spring is
arrested or suspended moult in LBBG in spring [see e.g. Jonsson in
Birding World 1998 and Rauste in Limicola 1999: p 156 plate 31, p 157 table 32,
p 159 plate 36, p 162 plate 40 & 41]. In suspended moult, there is a break
in primary moult. Moult may be suspended during migration, so there is no gap in the wing, which might
otherwise hamper efficient flight and maneuverability. After migration,
suspended moult is picked up at the point
where it stopped before the break. In arrested moult, a new moult-wave starts
at the first primary P1. In some cases two waves can be found: halfway the
wing moult continues after suspension and simultaneous moult
starts at P1. In Western Europe, all these moult strategies can be found in intermedius.
Approximately 3-10% of 3cy intermedius and graellsii LBBG show
arrested or suspended moult in spring and early summer. Arrested or
suspended moult in West European LBBG may correlate with migration distance. It seems reasonable to presume these
LBBG
belong to the race intermedius. Intermedius is, more than
graellsii, a long-distance migrant and needs more time and energy to fulfill
the journey back to Scandinavia. Energy can be saved by suspending the moult.
 Here
are two 3cy LBBG with arrested moult: a 3cy LBBG (right), seen on April 19 2003,
Maasvlakte and a 3cy LBBG (left) was seen July
07 2001,
IJmuiden, the Netherlands. They show arrested
moult in the primaries at P7 (right) and P6 (left). The grey tone is in line
with immature Dutch intergrades and intermedius and too pale for fuscus. In the tail, the central feathers have been
replaced by fresh white feathers. Some fresh third generation rectrices still have black central markings. Note the pale yellow legs.
Spring 2001, over 40 birds
showing arrested moult were encountered in Belgium and the Netherlands, by only
four observers.
 Here
are two other LBBG (intermedius?): one 3cy
(left) from Le Portel, NW
France, May 17 2002. It is actively growing P8. And a 3cy
(right), photographed June 30 2001, IJmuiden, the Netherlands. It shows very
advanced moult: almost all upper-parts were moulted and there is arrested moult in
the primaries. In the section 'accurate ageing', another LBBG is mentioned: a 3cy
LBBG Dutch intergrade in the Maasvlakte colony, May 27 2003. Arrested
moult can still be recognized by late August, as the next individual clearly
shows: a probable 3cy LBBG intermedius
on August 29 2003, IJmuiden, the Netherlands, with arrested moult at P8.
 Sometimes
the distinction between the tips of P5 and P6 is very obvious, although they are
the same generation and moult has not been suspended. P5 is the last primary
hidden by the tertials and therefore less exposed to sun-light and severe
weather conditions. In the picture right, July 7 2001, IJmuiden, the Netherlands,
the tip of P5 looks much fresher than the tip of the next primary P6. The difference may become even more
obvious by late summer. In real arrested moult, it's often the
complete feather that looks more bleached, with a brown hue. To determine
arrested moult between P5 and P6 may be difficult, while division between two
generation primaries is easier to establish between any other two
primaries.
How
do you recognize fresh feathers? By the tips, which do not show any wear. Fuscus
returns with pretty fresh primaries in northern Europe, especially when moult is
suspended or arrested during migration. But intermedius may show very
fresh primaries as well in spring, although the primaries must have been half a
year of age. See e.g. this intermedius type
sub-adult (5cy?) from June 17 2001, Maasvlakte, the Netherlands. Another
intermedius showing fresh primaries in spring could be view in a
previous paragraph.
Those
3cy showing arrested moult may otherwise look like the average LBBG in their
age-class. Here is a 3cy, May 11 2001,
Maasvlakte, the Netherlands. P1-P7 show
white tips on fresh primaries. P8-P10 are still second generation and P10 has no
white mirror. Arrested
moult is a rare phenomenon, but when intermedius show
arrested moult in the primaries, combined by advanced moult in the upper-parts,
these birds can easily be mistaken for fuscus. 
At Le
Portel, France, three such kind of LBBG were present early May 2001, including a
very dark, gentle (female) intermedius. The
bird's characteristics strongly approached those said to be diagnostic for fuscus.
Another intermedius
at the beach is depicted here.
In
Belgium, a colour-ringed intermedius (JUH6) with arrested moult at P9 was seen
on May 27 2001. The bird was seen before in Morocco (58.03
N - 06.40 E) in February 2001. It was ringed at the south coast of Norway
(Vest Agder county). The tail contained a few all-white feathers and the primary tips on
P1-P9 were obvious.
The
article of Lars Jonsson in BW 1998 gives excellent insight in the features and moult
strategy of Baltic fuscus. However,
it remains to be seen whether these points fully exclude intermedius. Very
dark (black) gentle (female?) second summer intermedius, which
show very advanced moult in the upper-parts, combined with arrested moult in the
primaries do
occur and approach fuscus in
both coloration and general structure. At Dannes (France) a bird strongly favouring
fuscus is depicted here as
well. Characteristics mentioned in the previous paragraphs come together in such
3cy birds, but are they really fuscus?
So
far, this paragraph deals with 3cy and sub-adult intermedius and graellsii.
Most 2cy fuscus return to Scandinavia with second generation primaries and by
August, these 2cy birds may replace inner primaries to third generation. In NW
Europe, we haven't seen such advanced birds. The most advanced 2cy intermedius
show second generation wing-coverts, tail and even second generation secondaries.
Arrested primary moult in 2cy birds is very rare and so far not recorded in
ringed birds.
 Having
said this about birds in spring, arrested moult may also occur in autumn of
course, as this bird left shows,
a sub-adult photographed October 22 2001 at Westkapelle, the Netherlands with P8
moulted but P9-P10 still old. Another example can be found in the right
thumbnail: a bird with arrested moult at P1 in autumn, thought to be intermedius.
Autumn
2002, many adults and near-adults were checked on their primary moult pattern to
get a more detailed overview of the possible moult strategies than may occur in graellsii
and in intermedius. Typically, nominate fuscus show a step-wise
moult sequence, resulting in several visible sets of primary generations,
sometimes up to three sets. These sets are marked by a strong divide, visible in
the field. We presumed this feature to be possible for intermedius as
well, but we couldn't support the idea until autumn 2003. However,
a few LBBG, most certainly from NW European origin and probably in sub-adult
plumage were photographed autumn 2002 in NW Europe. While checking groups of
100's of intermedius and graellsii LBBG in October, about 5% of
the adult / near-adult birds shows a primary moult strategy indicating
suspension or 'near-suspension', often in the outer primaries. In the October
sub-adult section, illustrative examples are shown. Most interesting is
a presumed intermedius
showing three moult waves in the wing. The odd 2cy may suspend moult as
well, as this 2cy bird,
photographed on October 05 2002 at Boulogne-sur-Mer (NW France) shows. Moult
will be suspended at P8.
3cy
nominate fuscus always seems to return with a complete replaced tail in the summer
(Jonsson BW 1998, p. 309). These new rectrices may nevertheless show black
markings. Most important point to establish in the field is wear in the tips.
Tail-feathers that are a year of age show worn tips. Rectrices (as
in this 2cy example) which have black markings, but without wear in the tips
and which show a broad white fringe are almost certainly fresh feathers.
Normally,
3cy graellsii and intermedius LBBG in the
colonies show only small variation in general appearance.
But rectrices can show distinct differences: a clear tail-band, spaghetti pattern, black-and-white
variegate patterns to snow white. Snow-white third generation tails in
(presumed 3cy) intermedius occur. Often these 3cy are extremely hard to separate
from 4cy. An example of a 2cy (!) October intermedius with an almost
white tail can be found here.
2cy
intermedius and graellsii normally return with a juvenile tail and
start moulting the rectrices after arrival. However, some LBBG return with a complete
second generation tail.
Sometimes
feathers are replaced because the old ones are damaged (gulls fight
pretty much and primaries may get lost and have to be replaced). When a single
outer primary is replaced in only one wing (so obvious no parallel wing moult)
it's clear such individuals do not follow an aberrant moult strategy. Sometimes aberrant
moult is hard to establish. An individual may look very advanced in
moult, but when the bird turns around, the view is completely different. here is
a graellsii from Dannes (France), May 06 2001. An example of how important it is to
view both sides of a gull, since the tertials left and right are at a different moult stage.
At a dump near Groningen, the Netherlands a very strange 2cy was present
mid June 2001. At one side, all primaries were completely juvenile, the other
wing showed completely second generation primaries. The size, feather-pattern and
jizz were pretty fuscus-like.
 A
3cy(?) LBBG, July 06 2001, IJmuiden, the Netherlands which is in
many respects fuscus-like. The problem starts with correct ageing: is it
3cy or still 2cy? Bare parts advocate 3cy, but are these pointed outer primaries
still juvenile? There is arrested moult in the primaries (P1-P6 are new, P1 is
present and P7 is present). The new
scapulars are almost black, it's a small bird, slender, long-winged, short-legged and
the pale yellow bill appears almost parallel. The tail has a few all white feathers,
while some fresh feathers have black
markings. In
some respect, it resembles a figure in Jonsson's article (BW 1998, p. 305 figure
4). Are those recently moulted scapulars as pitch black as necessary for fuscus?
And what exactly is the lightest extreme in fuscus?
The right
image shows another 3cy with
arrested moult, at P7. It was photographed on September 02 2003, at
Westkapelle, the Netherlands. Fortunately, it was ringed in Norway. Another
example, of a probable 3cy fuscus was
mentioned in a previous paragraph.
Fuscus most probably occur in Western Europe. If only 1% of
the Scandinavian fuscus follow a western migration route, dozens can be
expected annually in NW France, Belgium and the Netherlands. Unless
ringed, it's hard to get a clear view of the exact figures, since most features
in fuscus seem to apply to at least some intermedius
as well. This is not necessarily a problem when you see these gulls as clinal races of
one species: Lesser Black-backed Gull; and subsequently threat them as such: a
cline in colour and jizz from big and pale graellsii in the U.K.
to darker intermedius, ending in a small all-black fuscus in eastern
Scandinavia. And all types, forms or whatever you call them in between.
Within
this group, some spend winter far south, making another primary moult strategy necessary, while
others remain in the neighbourhood of the breeding grounds and follow the
familiar moult strategy seen in e.g. Herring Gulls (L. argentatus). Some take a
western and some take an eastern migration route. On population level, division
lines can be drawn, but on individual level this is very difficult. Problems
certainly arise when you threat these races as separate species, while there is
no sufficient knowledge of the variability in characteristics to recognize them in
the field.
This
page deals with problems separating immature fuscus from intermedius
and adults in autumn. A low primary moult score (un-moulted old primaries or arrested moult at
P1 or P2)
may indicate fuscus, but this phenomenon occurs in graellsii
& intermedius
as well.
Some 40% of adult graellsii
may arrest moult at the end of the breeding season. Without doubt
including individuals just moulting up to P1 and P2...
All
comments are much appreciated.
Many
thanks to: Norman van Swelm, Rik Winters, Peter
Adriaens, Peter Stewart, Visa Rauste and many others.
This
is an ORG-publication: The Organisation for Research on Gulls supports
cooperative field research and gull studies.
Mars
Muusse, Theo Muusse & Bert-Jan Luijendijk
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