Yellow-legged Gulls in the Atlantic-Mediterranean

Intersection Area

Nick Rossiter

nrossiter@supanet.com

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 NR’s maps) are from other workers

Classification - Leg Colour: YL yellow legs

Classification - Mantle Shade: cf Med. michahellis: S same, D darker, P paler

Classification - Size: cf Med. michahellis: S same, Less smaller

Table 1: Biometrics (in mm) of Herring L .a. argenteus, Yellow-leggedand Lesser-black Backed Gulls L. f. graellsii.

Feature argen-teus

Medmicha-hellis

Atlantic Yellow-legged Gull graell-sii

NWIberia

W Iberia NWAfrica

Macro-nesia

Source Cramp(1983)

Cramp(1983)

Carreraet al(1987)

Cramp(1983)

Urban etal (1986)

Cramp(1983)

Cramp(1983)

wing 404-425

438-460 419 401-431 420-439 423-437 406-427

tail 160-170

169-179 - 158-169 162-170 165-173 152-164

bill 48.9-53.2

51.5-56.6

54.8 49.5-53.6

49.4-55.7

49.1-51.5

47.7-52.1

tarsus 60.5-65.2

64.5-70.6

65.6 60.3-64.4

61.6-65.0

62.7-64.7

60.3-65.2

toe 56.7-61.6

59.2-65.4

- 55.2-59.3

- 58.7-60.3

52.5-56.3

Table 2a: Further Biometrics (in mm) of Atlantic Islands Yellow-leggedGulls.

Feature Atlantic Islands Yellow-legged Gull

Macro-nesia

Azores Azores Canaries(East?)

Canaries-Tenerife

Azores

Source Cramp(1983)

Dwight(1922)

Dwight(1925)

Banner-man(1963)

Volsøe(1951)

Vaurie(1965)

wing 423-437 401-423 402-421

401-418 417-440 418-438

tail 165-173 162-170 162-171

162-170 - -

bill 49.1-51.5 50.3-55.1 50.2-54.3

46.5-54 - -

tarsus 62.7-64.7 61.7-66.6 61.6-66.3

62.5-65.5 - -

toe 58.7-60.3 52.3-56.0 52.2-55.2

- - -

Table 2b: Further Biometrics (in mm) of Mediterranean Yellow-leggedGulls.

Feature Mediterranean Yellow-legged Gull

Medi-terranean

Camargue BalearicIslands

IslasCharafinas

Source Cramp(1983)

Isenmann(1973)

Carrera(1987)

Carrera(1987)

wing 438-460 440-465 447 457

tail 169-179 - - 178

bill 51.5-56.6

56-61 57.4 56.6

tarsus 64.5-70.6

67-72 70.3 68.5

toe 59.2-65.4

- - -

Classification - Structure: T tall & proud, SS short legs & stocky, SF short legs & finer features

Adult Mediterranean michahellis, Royan, August 1991

Adult Yellow-legged Gull atlantis, Lanzarote, August 1992

Adult summer Yellow-legged Gull, Agadir, April 2000

Porto, March 2001, Pair YLG adults

Noja (Santander), August 1990, 3s Cantabrican YLG

Classification - Wingtip: MWMB much white & much black, LWMB less white & much black (>=80% solid

black triangle, <=30% mirror P9), MWLB much white & less black

Typical Adult Wingtip, Yellow-legged Gull, Agadir, April 2000

Typical Adult Wingtip Yellow-legged Gull atlantis, Fuerteventura, April 2000

Two Adult Yellow-legged Gull, Setubal, March 1999

Minho, April 2001, ‘YLG’ adult

Classification - Wingtip on P9 in South: LWP9 mirror on P9 <=20% of birds, MWP9 mirror on P9 >20% of

birds

Classification - Calls (long): A like argenteus (possibly deeper), M like Med. Michahellis, SG like shrill

graellsii, AM even argenteus & shrill graellsii

Map for Canary Islands

Classification - Calls (mew): A like argenteus, M like Med. michahellis, G like graellsii, AG mixtures of

argenteus & graellsii

Classification - Forms (NR): MM Med. michahellis, C Cantabrican Atlantic YLG, D dark Atlantic YLG, DC cline

from dark to Cantabrican.

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.

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.

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.

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.

‘YLG’: Mauritania, Azores; Kelp Gull (Birding World)

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.

The Atlantic-Mediterranean Intersection Zone

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)

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

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

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

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)

Med YLG habitat - near Sanlúcar

Med YLG habitat - near Barbate

Med YLG habitat - near Conil

Med YLG - Conil August 2001

Med YLG - Conil August 2001 (with LBBG, Audouin’s)

Bimodal population at Conil -- very small numbers of dark YLG

Bimodal -- same group

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)

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

Med YLG distribution: within red line in marismas

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

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

Cliffs at Barbate

Cliffs at Barbate 2

Two Atlantic YLG at Barbate

Two Atlantic YLG at Barbate

Adult Atlantic YLG, at Barbate, June 2002

Adult Atlantic YLG at Barbate, June 2002

Adult Atlantic YLG at Cádiz, August 2001

Adult Atlantic YLG at Cádiz, June 2002

Med/dark YLG distribution: Med: red line in marismas; dark: blue line on cliffs

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

Tarifa YLG (2s) June 2002

Tarifa adult, June 2002

Tarifa adult, August 2001

Estepona YLG, 1s/2w (juv,1s, adult), August 2001

Estepona YLG 2s-3w, August 2001

Estepona YLG, 3s, June 2002

Estepona YLG 2s, June 2002

Estepona YLG 2 ad, June 2002

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.

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.

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.

Overall Statistics for Wingtip: C Cantabrican, DC Dark-Cantabrican cline, D Dark, I intersection, M Med YLG

(Conil)

P10- S

Tip%

LM%

SM%

P9%

P6-P10Tri -S

Sol%

SI%

LI%

P5 -S

BB%

TB%

IN%

P4 -PN%

C 27 73 27 0 85 28 0 30 70 16 6 63 31 10

DC 70 19 80 1 39 50 54 37 9 48 54 21 25 10

D 314 41 48 11 22 253 87 12 1 275 47 30 23 10

I 40 57 38 5 32 16 76 18 6 34 62 30 8 44

M 20 80 20 0 35 3 100 0 0 12 67 25 8 38

Overall Statistics for Calls: C

Cantabrican, DC Dark-Cantabrican cline, D Dark, I intersection, M Med YLG (Conil)

Long --graellsii

%

shrillgraellsii

%

Deeparg-

enteus %

MedYLG

%

Mew -graellsii

%

arg-enteus %

MedYLG

%C 0 0 100 0 0 100 0

DC + 68 32 0 85 15 0

D 8 58 34 0 75 25 0

I 0 77 11 12 85 6 9

M 0 0 0 100 0 0 100

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

– Jonsson’s studies in Marbella• No major divergence from Med YLG reported

– Carrera’s studies at Chafarinas Islands (300km E of Straits)

• Indicate that biometrics are similar to those of Med YLG

Med/dark/inter YLG distribution: Med: red line in marismas; dark: blue line on cliffs;

inter: yellow line on cliffs

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

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