Yellow-legged Gulls in the Atlantic-Mediterranean Intersection Area

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Yellow-legged Gulls in the Atlantic-Mediterranean
Intersection Area

• Nick Rossiter
• nrossiter_at_supanet.com

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Maps for Atlantic YLG showing results from
Various Classifications

• Primarily based on statistics held at
• http//www.nrossiter.supanet.com/ylg/
• First for adults from present studies
• Then from genetic studies of Liebers, D, Helbig,
  A J, and de Knijff, P,
• Azores data (in NRs maps) are from other workers

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Classification - Leg Colour YL yellow legs
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Classification - Mantle Shade cf Med.
michahellis S same, D darker, P paler
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Classification - Size cf Med. michahellis S
same, Less smaller
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Classification - Structure T tall proud, SS
short legs stocky, SF short legs finer
features
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Adult Mediterranean michahellis, Royan, August
1991
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Adult Yellow-legged Gull atlantis, Lanzarote,
August 1992
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Adult summer Yellow-legged Gull, Agadir, April
2000
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Porto, March 2001, Pair YLG adults
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Noja (Santander), August 1990, 3s Cantabrican YLG
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Classification - Wingtip MWMB much white much
black, LWMB less white much black (gt80 solid
black triangle, lt30 mirror P9), MWLB much white
less black
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Typical Adult Wingtip, Yellow-legged Gull,
Agadir, April 2000
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Typical Adult Wingtip Yellow-legged Gull
atlantis, Fuerteventura, April 2000
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Two Adult Yellow-legged Gull, Setubal, March 1999
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Minho, April 2001, YLG adult
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Classification - Wingtip on P9 in South LWP9
mirror on P9 lt20 of birds, MWP9 mirror on P9
gt20 of birds
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Classification - Calls (long) A like argenteus
(possibly deeper), M like Med. Michahellis, SG
like shrill graellsii, AM even argenteus shrill
graellsii
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Map for Canary Islands
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Classification - Calls (mew) A like argenteus, M
like Med. michahellis, G like graellsii, AG
mixtures of argenteus graellsii
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Classification - Forms (NR) MM Med. michahellis,
C Cantabrican Atlantic YLG, D dark Atlantic YLG,
DC cline from dark to Cantabrican.
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Genetic Studies

• Liebers, D, Helbig, A J, and de Knijff, P,
  Genetic differentiation and phylogeography of
  gulls in the Larus cachinnans-fuscus group (Aves
  Charadriiformes), Molecular Ecology 10 2447-2462
  (2001).
• michahellis has a more shallow haplotype and
  lower nucleotide diversity than atlantis
• its haplotypes are a subset of atlantis,
  suggesting that michahellis is derived from
  atlantis as the older lineage.
• atlantis has held a large population over a long
  period, residing in an area of relative climatic
  stability.

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Differentiations found

• michahellis population is less diverse than
  atlantis with no significant geographical
  variation while there is significant
  differentiation within all five atlantis colonies
  analysed.
• Unexpected differentiation was found between
  northern atlantis (Azores, west Portugal and
  Galicia) and southern atlantis (Madeira,
  Morocco). Since northern atlantis is similar to
  michahellis in many respects, this suggests that
  southern atlantis contributed little to
  michahellis.

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Classification - Forms (Liebers) MM Med.
michahellis, SA southern atlantis, NA northern
atlantis. Samples came from sites in green.
Notes extension (by NR) to Canaries needs to be
confirmed Cantabrican omitted from study.
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Convergence but ...

• Considerable agreement between studies.
• Some problems remain.
• Liebers et al consider that the Azores should be
  in the northern atlantis group
• but most earlier authors considered they belong
  to the southern group.
• However both Jonsson (1998) and Dubois (2001) did
  think the Azores form was distinct from the
  Canaries one.

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YLG Mauritania, Azores Kelp Gull (Birding
World)
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Convergence but 2

• Another problem is the lack of genetic
  information on the Cantabrican form and the
  argenteus of south west France.
• Gene flow between atlantis and michahellis is
  probably continuing because of intersection at
  Gibraltar
• Also michahellis is breeding now on the Atlantic
  coast of France further increasing the likelihood
  of genetic exchange with atlantis.

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The Atlantic-Mediterranean Intersection Zone
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Visits up to 2001

• Morocco
• Tanger (August 1993, 1994 and 2001)
• Asilah to the south west of Tanger (August 1994)
• east Andalucia
• Nerja and Estepona (May 1996 August 2001)
• west Andalucia
• Cádiz, Conil and Barbate (August 2001)
• Straits of Gibraltar
• Tarifa, Gibraltar and La Linea (August 2001)

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Visits in 2002

• The detailed results of a more recent visit in
  June 2002 to west and east Andalucia are not
  available yet
• Visited Estepona, Tarifa, Barbate, Conil, Cádiz
  and Sanlúcar
• Some pictures will be shown

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Three main forms in Zone in 2001

• Mediterranean Yellow-legged Gulls
• marshes, lagoons and marismas
• dark Atlantic Yellow-legged Gulls
• harbours and rocky cliffs in west Andalucia at
  Cádiz and south-west of Tanger at Asilah
• Intersection Mediterranean/dark Atlantic
  Yellow-legged Gulls
• harbours and rocky cliffs in the immediate west,
  centre and east of area

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In June 2002

• Numbers of Mediterranean Yellow-legged Gulls
  reduced but same habitat
• Large YLG colonies at Barbate cliffs and the
  islands off Cádiz were of dark form
• Gulls further east similar (provisionally) to
  those in August 2001

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Features of Med YLG

• Large size being considerably bigger than
  graellsii.
• Relatively pale mantle, lacking obvious blue
  tones.
• Boxy heads, long heavy bill with blunt tip,
  sturdy long legs equal in length to height of
  body above.
• Head moult most (60) brown speckles over
  forehead and rest of head (not neck) remainder
  fairly white still.
• Leg colour was a pale yellow with a slight orange
  tint
• Bill was a rather washed out yellow with a not
  very strong orange-red gonydeal spot.
• Calls mew like a deep graellsii the long deeper
  than graellsii and hoarser (more guttural).
• Only 35 with mirror on P9 (see Dwight)

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Med YLG habitat - near Sanlúcar
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Med YLG habitat - near Barbate
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Med YLG habitat - near Conil
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Med YLG - Conil August 2001
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Med YLG - Conil August 2001 (with LBBG, Audouins)
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Bimodal population at Conil -- very small numbers
of dark YLG
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Bimodal -- same group
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Comparison from notes -- dark form showed (cf Med
YLG)

• Yellow-ochre legs (more ochre than pale yellow)
• Shorter legs (2/3 body, not 1/1 body, similar in
  length to LBBG)
• Darker mantle
• Blue-grey tinge (not wane grey)
• More mottled on front of head (not fine speckles)
  
• More compact appearance
• Rounded head (not boxy)
• Size much smaller (slightly bigger than LBBG)
• Tamer (kept in group while Med YLG left)

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Med YLG elsewhere

• In August found in small numbers in harbours
• Tanger (7 in 2001, 10 in 1993-94)
• Tarifa (20 in 2001)
• Further east (cannot quantify)
• Figures for Tanger and Tarifa based on birds
  showing all features of Med YLG

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Med YLG distribution within red line in marismas
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Atlantic YLG to West

• In August predominate in harbours at Cádiz (90km
  from Straits) and Asilah (50km from Straits)
• In June breed on cliffs at Barbate (40km from
  Straits) and on islands (forts) off Cádiz
• These colonies do not contain Med YLG

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Features of YLG to west

• close to the dark form in
• mantle shade with a dark blue-grey colour
• stocky structure
• relatively small size
• calls with shrill graellsii-like long calls and
  graellsii-like mew calls.
• but perhaps slightly more white on P9

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Cliffs at Barbate
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Cliffs at Barbate 2
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Two Atlantic YLG at Barbate
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Two Atlantic YLG at Barbate
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Adult Atlantic YLG, at Barbate, June 2002
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Adult Atlantic YLG at Barbate, June 2002
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Adult Atlantic YLG at Cádiz, August 2001
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Adult Atlantic YLG at Cádiz, June 2002
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Med/dark YLG distribution Med red line in
marismas dark blue line on cliffs
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Intersection Mediterranean/Atlantic YLG

• In harbours and rocky cliffs in the immediate
  west, centre and east of area
• some characteristics of dark Atlantic YLG
• increasing tendency to Mediterranean form

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Tarifa YLG (2s) June 2002
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Tarifa adult, June 2002
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Tarifa adult, August 2001
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Estepona YLG, 1s/2w (juv,1s, adult), August 2001
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Estepona YLG 2s-3w, August 2001
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Estepona YLG, 3s, June 2002
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Estepona YLG 2s, June 2002
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Estepona YLG 2 ad, June 2002
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Features Estepona YLG 1 (cf dark Atlantic YLG)

• Mantle most are a similar blue-grey to that
  further west but a minority are a more leaden
  grey.
• Size significantly larger.
• Structure heavier
• more adults (30 as against 7-10 in Tanger) have
  boxy heads
• legs are generally longer being 80-90 of the
  height of the body above compared to 70 in
  Tanger and 100 in Mediterranean michahellis.
• At rest the heavier heads were not tucked into
  the neck but were held with the bill pointing
  downwards as in Mediterranean michahellis.

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Features Estepona YLG 2 (cf dark Atlantic YLG)

• Primaries
• slightly more white with 60 showing a white tip
  on P10 and 40 a mirror on P9.
• more black on P5 with 75 showing a broad band.
• Bare parts bills were a rather dull yellow with
  a diffuse orange-red gonydal spot legs were a
  dullish ochre-yellow.
• Calls considerable variation perhaps reflecting
  the genetic mixing.
• Most long calls (55) are of the shrill graellsii
  type as in Tanger but 30 are guttural, as in
  Mediterranean michahellis, and 15 are a deep
  argenteus.
• Mew calls show a similar mixture.

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Features Estepona YLG 3 (cf dark Atlantic YLG)

• First-years
• 75 of the tertials were like those in the
  Canaries with a narrow pale fringe
• 25 were different to any found in the Atlantic
  showing, in addition to the narrow fringe, two
  slight notches on each feather edge.

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Overall Statistics for Wingtip C Cantabrican,
DC Dark-Cantabrican cline, D Dark, I
intersection, M Med YLG (Conil)
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Overall Statistics for Calls C Cantabrican, DC
Dark-Cantabrican cline, D Dark, I intersection, M
Med YLG (Conil)
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Further East

• Studies
• Limited ones by NR in Nerja (west of Malaga,
  170km E of Straits)
• 75 are large and heavy like Med YLG, 25 are
  small and with relatively slight structure
• Jonssons studies in Marbella
• No major divergence from Med YLG reported
• Carreras studies at Chafarinas Islands (300km E
  of Straits)
• Indicate that biometrics are similar to those of
  Med YLG

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Med/dark/inter YLG distribution Med red line in
marismas dark blue line on cliffs inter
yellow line on cliffs
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Width of Intersection Zone

• Barbate 40km W of Straits of Gibraltar
• Nerja 170km E of Straits of Gibraltar
• Does not appear to be greater than 210km.
• May be less if assess coastline more completely
  for colonies

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Comparison of SW Spain and SW France (Yésou)

• Med YLG are invading both areas and breeding in a
  particular biotope (marismas, lagoons, salinas)
• dark Atlantic YLG in Spain appear to occupy a
  similar role to the argenteus in France, breeding
  on cliffs, islands and forts in SW Spain
• additional complication in SW Spain is the gene
  mixing zone across the Straits