nominate Lesser Black-backed Gull (L. f. fuscus)

(last update: 24-1-2015 )

Coordinators:
Amir Ben Dov (Israel)
Hannu Koskinen (Finland)
Mars Muusse (the Netherlands)

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fuscus rings

fuscus 1cy July
fuscus 1cy Aug
fuscus 1cy Sept
fuscus 1cy Oct
fuscus 1cy Nov
fuscus 1cy Dec

fuscus 2cy Jan
fuscus 2cy Feb
fuscus 2cy March
fuscus 2cy April
fuscus 2cy May
fuscus 2cy June
fuscus 2cy July
fuscus 2cy Aug
fuscus 2cy Sept
fuscus 2cy Oct
fuscus 2cy Nov

fuscus 2cy Dec

fuscus 3cy Jan
fuscus 3cy Feb
fuscus 3cy March
fuscus 3cy April
fuscus 3cy May
fuscus 3cy June
fuscus 3cy July
fuscus 3cy August

fuscus 3cy Sept

fuscus 3cy October
fuscus 3cy Nov
fuscus 3cy Dec

fuscus 4cy Jan
fuscus 4cy Feb
fuscus 4cy March
fuscus 4cy April
fuscus 4cy May
fuscus 4cy June
fuscus 4cy July
fuscus 4cy Aug
fuscus 4cy Sept

fuscus 4cy Oct
fuscus 4cy Nov
fuscus 4cy Dec

fuscus ad Jan
fuscus ad Feb
fuscus ad March
fuscus ad April
fuscus ad May
fuscus ad June
fuscus ad July
fuscus ad Aug
fuscus unringed Aug
fuscus ad Sept
fuscus ad Oct
fuscus ad Nov
fuscus ad Dec

2cy fuscus: May

Before departing to the wintering grounds, some juvenile fuscus moult several mantle feathers and scapulars to second generation feathers. Migration may start early, with juvenile birds arriving in Africa by late September, but most arrive in October, in some cases in complete juvenile plumage. Normally an extensive moult starts after arrival: scapulars, coverts, secondaries and primaries are often all included in the early complete moult on the wintreing grounds. By April, some 2cy birds migrate north to the breeding areas. On arrival, the wing may look anything from only a few new replaced feathers to completely 2nd generation primaries. Sometimes, moult is arrested during migration and a clear division is visible between outer old juvenile primaries and fresh 2nd generation primaries.

Primary moult of Baltic Gull during the first 15 months (in: Dutch Birding 28: 158-161)
Hannu Koskinen & Visa Rauste (Finland)

The moult strategies of the members of the Lesser Black-backed Gull complex have been studied extensively during the last decade. Jonsson (1998) was the first to describe moult patterns of nominate fuscus during the first winter and summer: the most frequent pattern is a complete moult before the first summer, but there are lots of variation. Rauste (1999) gave some quantative data of the subject. As these data comprised only 19 ringed birds, they left much room for discussion.

Subsequent studies have revealed that the difficulties of subspecific identification were severely underestimated in the 1990's (Gibbins 2004, Winters 2006, pers. obs), as moult patterns proved much more variable. It has also become obvious that unknown but possibly significant numbers of western taxa (L. f. intermedius, L. f. graellsii, hereafter intermedius and graellsii respectively) may occur in Finland in addition to the local subspecies fuscus and the fourth member of this complex, Heuglin's Gull, Larus heuglini (hereafter heuglini) (pers. obs.). This casts some doubts on the homogeneity of the data set used by Rauste (1999). Thus, the reliability of Rauste's results have been questioned with good reason.

To study the primary moult with more reliable material we have assembled a data base of birds which have been ringed as chick in Finland (n=49) or Eastern Sweden (n=4) and that were observed in Finland during their second calendar year. Table 1 shows the phase of primary moult of these birds. It seems to confirm the results of Rauste (1999): in addition to the early moulting majority there is a long ‘tail’ in the distribution of moult scores. The least advanced individual had not even started its primary moult before its arrival in Finland. 66% had completed the first primary moult before returning to Finland, which is comparable with the estimate given by Rauste (1999) of 60-70%. Most of the birds which had completed the first moult started the second primary moult during the summer and this moult can proceed to P4. Five individuals had two simultaneous moult waves in the primaries (‘Staffelmauser’ which is known from older age classes of fuscus since Stresemann and Stresemann 1966). It is also worth noting that the most advanced birds were more than one whole primary moult cycle ahead of the least advanced ones. Such wide variation has probably not been documented in any taxon with such a restricted range and homogeneous migration strategy.

The Finnish breeding population has been considered very homogeneous, all birds being typical fuscus. However, there are records of birds which have been ringed as chick in Southern Finland that have nevertheless developed a paler mantle in (sub)adult plumage. The palest of these birds have a mantle shade which is very close to typical graellsii or heuglini.

It may be a matter of opinion or definition what these paler-mantled birds should be called. In spite of their appearance they have nevertheless hatched in the core range of fuscus. They may be considered as variation of fuscus, or as genetic influence of other taxa, in which case it is unclear if western (graellsii/intermedius) or eastern (heuglini) (or both!) birds are involved. Based on structure and other clues we think that these birds are more similar to western birds than that they resemble heuglini (Koskinen at all 2001).

The frequency of such birds is low: some six pale-mantled birds have been seen among c 1700 ringed fuscus in Tampere (less than 0.5%). Quite surprisingly, at least two such birds have been included in table 1: CYHP and CEVC have been seen and photographed in Tampere in 2005 as third caledar-year and both showed a significantly paler mantle than a typical fuscus. It is worth noting that, apart from the moult, also the plumage of CYHP in its second calendar-year caused lots of debate (see Gibbins 2004).

If we apply the strictest definition of fuscus and accept only those birds of which both provenance and appearance as an adult are known, there are only 27 such birds in our data set that fulfill these criteria (marked ‘YES’ in table 1 in the column ‘controlled as 2+cy’). Based on this limited number, the variation of the primary moult during the first winter seems to be equally variable as it is among all ringed birds together. This indicates that the variation in moult patterns is not solely due to the inclusion of birds of other populations, but rather that the variation is likely to be normal among fuscus.

Markkhu Kangasniemi, Hannu Kettunen, Janne Kilpimaa, Harri Kontkanen and Veijo Turunen contributed details to the moult data base. Risto Juvaste has organised the Finnish colour ringing project which is the base of this study. Ruud Altenburg, Dick Forsman, Mars Muusse and Rik Winters have commented on the manuscript.

References

Gibbins, C N 2004. Is it possible to identify Baltic and Heuglin’s Gull? Birding Scotland 7: 154-186.

Jonsson, L 1998. Baltic Lesser Black-backed Gull Larus fuscus fuscus – moult ageing and identification. Birding World 11: 295-317.

Koskinen, H, Kettunen, H & Kangasniemi, M 2001. Pale-backed Lesser Black-backed Gulls in Tampere. Linnut 36: 27-30 [in Finnish].

Rauste, V 1999. Kennzeichen und Mauser von ‘Baltischen Herringmowen’ Larus fuscus fuscus und ‘Tundramowen’ Larus fuscus heuglini. Limicola 13: 105-128, 153-188.

Stresemann, E & Stresemann, V 1966. Die Mauser der Vogel. J Ornithol 107, Sonderheft.

Winters, R 2006. Moult and plumage variation in immature Lesser Black-backed Gulls in the Netherlands. Dutch Birding 28: 140-157.

Tables

Table 1: Moult phase of primaries of Finnish and Swedish Lesser Black-backed Gulls Larus fuscus. Details analysed from photographs with some additions from field notes. Observations sorted by date, except when several records available of same bird in different moult phases, in which case first and last records are given in succession without repeating ring code. Entrance 'PALE' in the column 'controlled as 2cy+' means that the bird was observed after its second calendar year and showed upperparts much paler than typical fuscus.
.
colour + ring code
date
controlled as 2cy+
P1
P2
P3
P4
P5
P6
P7
P8
P9
P10
1
HT 233 118 4 May 2004
No
2
W CEVC 12 May 2004
PALE
3
W CRXA 13 May 2005
.
4
SVS 8106017 18 May 2003
No
5
W C3J1 24 May 2003
Yes
.
. 22 June 2003
.
6
W CJJR 28 May 2005
.
.
. 28 Aug 2005
.
7
W C5H0 1 June 2002
No
8
W CYHP 2 June 2004
PALE
.
. 21 Aug 2004
.
9
W C1NU 3 June 2001
Yes
10
W CHYE 7 June 2003
Yes
.
. 29 June 2003
.
11
CT 115523 11 June 2000
No
12
W MC24 14 June 2003
Yes
13
HT 106366 15 June 1999
Yes
14
W CAA3 15 June 1999
No
15
W C6JR 21 June 2000
No
16
W C4AJ 23 June 2000
Yes
17
W C2WJ 25 June 2002
Yes
.
. 17 Aug 2002
.
18
W MC78 29 June 2003
No
19
W COXX 30 June 2002
Yes
20
W C5MW 30 June 2002
Yes
21
HT 210035? 01 July 2000
No
22
W CRWC 01 July 2005
.
23
W C5WS 04 July 2003
Yes
24
W C9NS 09 July 2002
Yes
25
HT ? 08 July 2004
.
26
SVS 8105890 10 July 2003
No
27
W C4ES 13 July 2000
Yes
28
W C3C6 15 July 1999
Yes
.
. 26 July 1999
.
29
W C5AR 04 July 2001
Yes
30
W CJUC 17 July 2003
Yes
31
W C90E 17 July 1998
No
32
W C08C 17 July 1998
Yes
33
W CUJK 18 July 2004
No
34
W C6XV 09 July 2002
Yes
.
. 03 Aug 2002
.
35
W C3VS 19 July 2003
Yes
36
W C683 20 July 2004
No
.
. 30 July 2004
.
37
R CPC1 25 July 2005
.
.
. 11 Sept 2005
.
38
W C6H5 28 July 2002
Yes
39
W C9H6 30 July 1998
Yes
40
HT ? 30 July 1998
.
41
W C9M7 01 Aug 1998
Yes
42
W C78J 01 Aug 1998
Yes
43
W C5UJ 02 Aug 2002
Yes
.
. 17 Aug 2002
.
44
HT ? 03 Aug 1999
.
45
W CZ91 05 Aug 2001
No
46
W C316 06 Aug 1998
No
47
R C7MV 06 Aug 2005
.
48
W CJK4 09 Aug 1999
Yes
49
HT 246209 15 Aug 2004
Yes
50
W C5S5 24 Aug 1998
.
51
W C13C 25 Aug 1998
Yes
52
R CSA2 31 Aug 2005
.
53
W CES0 01 Sept 2000
Yes
colour codes for primaries:
juvenile
2nd generation
2nd generation growing
3rd generation
3rd generation growing
missing
feather not seen

1cy fuscus in August, ringed in Finland. (81365 bytes)Larus fuscus fuscus 2cy CUCC May 16 2007, Tampere, Finland (61.33N 24.59E). Images Hannu Koskinen.
L. f. fuscus in July, ringed in Finland. (97367 bytes)fuscus 2cy CJJR, May - August 2005, Tampere, Finland (61.33N 24.59E). Pictures Hannu Koskinen & Visa Rauste.Slightly delayed bird in spring.
1cy fuscus in August, ringed in Finland. (81365 bytes)Larus fuscus fuscus 2cy C06H May 29 2011, Ämmässuo dump, Espoo, S Finland. Picture: Visa Rauste.
P8-P10 old juvenile.
1cy fuscus in August, ringed in Finland. (81365 bytes)Larus fuscus fuscus 2cy C59J May 31 2011, Ämmässuo dump, Espoo, S Finland. Picture: Visa Rauste.
P1-P10 2nd gen.
L. f. fuscus in July, ringed in Finland. (97367 bytes)fuscus 2cy CLJ7 May 31 - July 04 2013, Koukku, Finland. Image: Hannu Koskinen. P1-P10 juvenile, complete moult starting in summer.
1cy fuscus in August, ringed in Finland. (81365 bytes)Larus fuscus fuscus 2cy CSX2 May 14 2010, Eilat, Israel. Picture: Amir Ben Dov.
All feathers included in first moult on wintering grounds.
HIGH-RES IMAGE (25,9 MB)
1cy fuscus in August, ringed in Finland. (81365 bytes)Larus fuscus fuscus 2cy CRF3 May 23 2009, Tampere, Finland. Images Hannu Koskinen.
All feathers included in first moult on wintering grounds.
1cy fuscus in August, ringed in Finland. (81365 bytes)Larus fuscus fuscus 2cy CJC9 May 25 2006, Amsterdam, The Netherlands. Images Ruud, Theo, Ronald, Arnoud.Delayed 2cy bird.
1cy fuscus in August, ringed in Finland. (81365 bytes)Larus fuscus fuscus 2cy C10H May 09 2007, Tampere, Finland. Images Hannu Koskinen & Markkhu Kangasniemi.2cy, also seen as juvenile & 3cy.
1cy fuscus in August, ringed in Finland. (81365 bytes)L f fuscus 2cy SVS 811x945 May 29 2007, Tampere, Finland (61.33N 24.59E). Images Hannu Koskinen.
1cy fuscus in August, ringed in Finland. (81365 bytes)L f fuscus 2cy SVS 8113224 May 16-17 2007, Tampere, Finland (61.33N 24.59E). Images Hannu Koskinen.
1cy fuscus in August, ringed in Finland. (81365 bytes)L f fuscus 2cy NOS 4248181 May, July & August 2006, Tampere, Finland (61.33N 24.59E). Images Hannu Koskinen & Markkhu Kangasniemi.2cy, also seen as 3cy & 5cy.
1cy fuscus in August, ringed in Finland. (81365 bytes)L. f. intermedius 2cy J5V1 May 24 2008, Amsterdam, the Netherlands. Images Ruud Altenburg. Juvenile intermedius from contact zone in N Norway. Also seen as 1cy in October.
1cy fuscus in August, ringed in Finland. (81365 bytes)L. f. intermedius 2cy JJ6S May 28 2006, Amsterdam, the Netherlands. Images Ruud Altenburg. Juvenile intermedius from contact zone in N Norway.
1cy fuscus in August, ringed in Finland. (81365 bytes)Larus fuscus fuscus 2cy May 14 2010, Eilat, Israel. Picture: Amir Ben Dov.
All feathers included in first moult on wintering grounds.
1cy fuscus in August, ringed in Finland. (81365 bytes)Larus fuscus fuscus 2cy May 14 2010, Eilat, Israel. Picture: Amir Ben Dov.
All feathers included in first moult on wintering grounds.
1cy fuscus in August, ringed in Finland. (81365 bytes)Larus fuscus fuscus 2cy May 13 2011, Eilat, Israel. Picture: Amir Ben Dov.
Mirror on P10.
1cy fuscus in August, ringed in Finland. (81365 bytes)Larus fuscus fuscus 2cy May 13 2011, Eilat, Israel. Picture: Amir Ben Dov.
All feathers included in first moult on wintering grounds.
1cy fuscus in August, ringed in Finland. (81365 bytes)Larus fuscus fuscus 2cy May 13 2011, Eilat, Israel. Picture: Amir Ben Dov.
All feathers included in first moult on wintering grounds.