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variation in moult strategies within the LBBG-complex is nearly larger
than the inter-specific variation in moult strategies between most other
European large gull-taxa.
To a certain extent this has been caused by intra-specific differences in
the geographical position of the winter-quarters. Concerning first summer
LBBGs, several authors highlighted the different
moult strategies between fuscus / heuglini and their western
relatives graellsii / intermedius in recent publications.
However, the articles were written on the assumption that intermedius
and graellsii share a similar moult strategy. Without questioning
the importance of these publications, we think the latter is a (too)
On the basis of concise descriptions and photographs of a few representative
individuals, we would like to give an impression of our observations made
over the last few years.
Currently, we recognize at least three types of 1st-summer LBBGs, which occur
in large numbers (up to 60 individuals daily) on migration during spring
and early summer at the Maasvlakte, the Netherlands (51.58
N, 4.02 E). Birds with
intermediate characteristics are certainly not rare, but at least a
considerable part is distinguishable.
Anyhow, we would like to stress that our classification has mainly been
based on the differences in plumage patterning or moult-timing.
From the few ring-recoveries from England and the Netherlands, we could
say that Dutch 1st summer LBBGs born at the Maasvlakte don't differ much
from the English same-aged graellsii.
Normally, the scapulars and mantle feathers have a pale or greyish base
with brown anchors or barring. The wing-coverts are usually completely
juvenile or juvenile with only a small number of 2nd generation coverts.
The tail is largely black-brown and nearly always juvenile (or at most a 2nd
generation R1). The under-parts and head are patterned with bold markings
on a dirty base. The bill is mostly blackish, with only a slightly paler
base. Legs are pink.
Nevertheless, in spring 2000 one Belgian colour-ringed individual showed a
suspended covert-moult process with 4 2nd generation greater
coverts, complete 2nd generation tertials, 8 2nd
generation median coverts and approximately the same number of 2nd
generation lesser coverts.
The first birds with active primary-moult in the inner primaries appear in
the last week of April (generally in NW France) and in the first week of
May at Maasvlakte, the Netherlands. Towards the end of the month, the number of birds
in active primary moult steadily grows.
From the beginning of June it is hard to find any individual which has not
shed any primary yet.
The quality of remaining juvenile primaries in spring is usually low,
caused by heavy bleaching and wear. The contrast between new and old
primaries is very obvious.
Regarding both types:
We believe 'core-representatives' of the 2nd and 3rd type are
morphologically different from 'core-first types' and probably belong to intermedius-populations.
They show a short neck, small rounded head, fine and short bill, short
legs (especially tibia) creating a delicate and compact appearance. In
some individuals this is pronounced by the relatively short primary-projection.
Also, plumage and the timing of moult in wing-coverts and tail-feathers
are on average different from the first type.
At first we would like to treat wing-covert, tail and primary moult in
The number of moulted tail-feathers in the winter-quarters is highly
variable and subsequently we find large variation in May and June.
Advanced individuals show a complete 2nd generation tail, while
others return with a clearly suspended moult-stage. In the
winter-quarters, many individuals do not proceed the moult of the
rectrices in a descendant sequence, since migrating birds in spring really
show every conceivable moult-stage (e.g. R5-6 2nd generation,
while R1-4 are still juvenile, etc).
Some birds do not show fully-grown rectrices, but it is at least not usual to
find a tail in active moult by May and the first half of June. Apart from
the obvious fresh white tips, the pattern of the 2nd generation
is mostly juvenile-like, but the darker parts are pure black and the
pattern is more vermiculated. However, birds with for example a partially
white R2, a nearly complete black R3 and with a R4 showing much white, are
common. A small minority shows only very little black on the 2nd
The renewed upper-tail coverts are completely white or with some sparse
barring on a white base.
The wing-covert moult has mainly been suspended prior to migration, with
in most cases a generation contrast between the inner and outer coverts.
This especially applies to the greater coverts, which often show a mix of
juvenile and 2nd generation coverts, together with tertials and median
coverts which have been renewed. The moult-stage of lesser coverts is
more advanced than in the greater coverts, but especially 'upper' lesser
coverts are less advanced than the tertials and median coverts.
Regarding the under-wing coverts and axillaries; it is often very difficult
to obtain good views to determine the generation. In advanced individuals,
these under-wing coverts are already partially or completely renewed and
sometimes nearly all-white. It might turn out that the moult of under-wing
coverts and coverts show similarity in moult strategy.
The onset of the primary moult in 2nd and 3rd type
2cy LBBGs in early summer is on average slightly later (1-2 weeks) than in
typical 1st types. Additionally, the individual variation is
more pronounced, with e.g. in the 3rd week of June, birds with
only P1-2 missing and birds which already shed P7. However, in
comparison with the first type, differences in timing of primary moult is
usually not significant.
An interesting phenomenon we encountered, was the sometimes remarkably
good condition of the remaining juvenile primaries. In a few cases we
experienced real difficulties in determining the generation of the
in the second type
short we will discuss the general variation of the 2nd type and
its difference from the 1st and 3rd type.
Compared with the first type we already stated that both second and third
type usually return to the breeding grounds (northern feeding grounds)
with some renewed wing-coverts, tertials and even regularly rectrices.
Besides other differences from the first type already covered under the
header 'regarding both types', juvenile tail-feathers in this type show
less blackish brown patterning on the base of the tail-feathers, causing a
less broad but more contrasting tail-band.
Even the under-parts are paler in the second type, with contrasting spots
mainly restricted to the flanks and lower hind-neck. The palest parts are
the breast and head.
In comparison with the 3rd type the under-parts are slightly
more patterned, especially on the flanks and hind-neck. The 2nd
generation upper-parts and wing-coverts show obvious barring and anchor-patterns on a pale or cold brownish grey
surrounded by a pale fringe in the second type. The tertials show contrastingly bold brown or
blackish barring on a white base (see photo 10 and
11) or only a blackish
brown base with a sub-terminal bar sharply demarcated from the pale tip
(like third type birds).
Moult-stage and even pattern of renewed feather tracts are on average less
advanced than in the third type. The upper-parts seem to be moulted in an
earlier stage than the wing-coverts, resulting in a 'wear contrast'
between fresher coverts/ tertials against heavier worn scapulars and
General information regarding the third
type and its difference from typical fuscus:
Our knowledge of fuscus is confined to published photographs and
limited field observations, but
there is little doubt that 3rd types may resemble fuscus
superficially. However, we have good reasons to believe this type belongs
to intermedius rather than fuscus. To name a few:
1. We have seen every conceivable moult stage (0-100%) in coverts,
tertials and tail feathers.
2. Although less often, comparable advanced moult stages occur in the 2nd
3. Returning birds with completely or partially moulted primaries
(suspended) are very rare.
4. Migration started from the beginning of May onwards, which is too early
for fuscus (arriving by July). The latter taxon only rarely reaches northern latitudes
Even if there appears to be intermediate characters, it remains unlikely
that birds of this type are a result of hybridisation between both taxa.
One would at least expect less high numbers on migration.
As stated earlier, we only have limited experience with fuscus. Based on
photographs in various magazines, we think that on colour and pattern of
plumage alone, some individuals are hard to separate from typical fuscus.
We feel that mahogany brown colours in coverts and tertials are rare in
typical 3rd types. In individuals with freshly moulted coverts, the
pattern we most often see is a blackish central wedge on a grey brown
base, broadening towards the tip, with near the tip some white.
Another common pattern is just a diffuse dark shaft on a grey-brown base,
and normally with some white near the tip. But remember that
patterns may become indistinct or even undetectable when feathers become
heavily worn and abraded.
In many birds, the mantle and wing-coverts have been replaced in one wave
and in such a case lack any 'wear contrast'. This sometimes results in
an already worn and bleached 2nd generation bird.
As shown in the images, typical 3rd types are quite easy to separate
from typical 2nd types on plumage colouration and pattern alone. The
under-parts are clean white, with only contrasting spots on hind-neck
and flanks. Like the second type, this type shows a paler bill-base. A few birds already have a pale-yellow
bill-base. Pale yellow
legs have also been noticed in this type, but surely not often.
Except for these three recognizable types,
individuals with serious characteristics of fuscus or with serious
characteristics of heuglini turn up in the Netherlands during spring and
early summer. Although we call these types simply fuscus-types
respectively heuglini-types, this is without the intention of treating
these birds as true representatives of both taxa.
It is possible that both types are aberrant individuals from the third or
(less probable) second type as discussed above. Lars Jonsson, in his article about identification of fuscus
LBBGs (Birding World, 1998) states: "probably the most obvious option is to
look for first-summer birds with a new set of flight feathers in
July-August." Some of these birds match this feature, as can be seen
in image 18.