Hybrid from the Netherlands
Posted: Thu May 30, 2013 9:15 am
Location: roof top breeding at police station Katwijk aan Zee (52.12.04.30 N ; 04.24.51.43 O). Address: Piet Heinlaan 140, Katwijk.
Ringer: Roland-Jan Buijs / Buijs Eco Consult.
Measurements & Photography: Roland-Jan Buijs / Buijs Eco Consult & Jeroen Nagtegaal / Hogeschool Larenstein.
Date: May 28 2013.
GREY TONE:
In the Netherlands, Herring Gull upper-parts is clearly paler than upper-parts of Lesser Black-backed Gulls, without any overlap in grey tone. The modal grey tone for the Herring Gulls sampled was 5 (range 3-7) and for Lesser Black backed Gull 11 (range 8-15). Samples are from the Moerdijk colony 2005 & 2006, sample size in Herring Gull: n = 292 and Lesser Black-backed Gull: n = 888. Measurements based on Agfa Grey Scale 0-20.
Grey tone of 8,5 in black K.B rules out typical Larus argentatus argenteus Herring Gull, breeding in the Netherlands, and also a deep coral red orbital ring and red gape is extremely rare (<0,5%) in breeding Herring Gull the Netherlands.
ORBITAL RING & GAPE:
Almost all Herring Gulls showed orange orbital rings (94%), with only 18 birds having yellow and one bird (HG NLA 5.363.004) a red orbital ring. Coral red is 'the classic' colour for Lesser Black-backed Gulls. Four Lesser Black-backed Gulls scored orange (LBBG yS8, y13, oC9, oTX), with all other individuals having red orbital rings. Sample for Herring: 284, and sample Lesser Black-backed Gull: 919.
All single characteristics in black K.B could just fit in Dutch Lesser Black-Backed Gull Larus fuscus graellsii, but the combination of features is highly unlike to occur simultaneous in a single bird:
- pale grey upper-parts (graellsii upperpart < grey 9,0 = 0,23%, n=888)
- no red nor black on upper mandible (graellsii no red on upper mandible = 39%), (graellsii no black on upper mandible = 19%). (graellsii no black on lower mandible = 32%)
- 6 primaries with sub-terminal black (graellsii primaries with sub-terminal black < 7 = 23%, n=931 in all breeding birds, n=869 in 5+CY birds / full adults)
- much white in P10 wing-tip. (graellsii no sub-terminal black or broken band on P10 = 17,5%, n=931)
- no black on primary coverts. (graellsii no black on coverts = 24%)
'Straw yellow' legs can be found in adult Larus fuscus graellsii, but saturated yellow legs are by far more common (no %).
Given the low %'s of occurrence of single features, and the low probability they occur simultaneously in a single graellsii bird (though some feature may correlate, like wing-tip pattern), the possibility this bird black K.B may be hybrid is real.
Then, speculation starts about parentage. This really is only speculation, as we know from ringed birds some offsprings don't show much similarity to any of the parents. Anyhow, michahellis x graellsii (several, about 30, mixed pairs annually in the Netherlands) would probably have rich yellow legs, red on upper mandible, not this much white on P10 tip, and also not such a long grey tongue on P7-P8 (grey running far down to feather tip, leaving only a narrow medial band). Also in this hybrid option, grey tone may be expected slightly darker.
Probably argenteus is involved, which has been expected to hybridise with graellsii in the past, but nowadays, with large populations of both species, hybridisation doesn't seem to occur anymore (at least, it is not documented over the last years as far as I know). Evidence of occurrence is green E433, hybrid pullus ringed on June 29 1995. This is different for argenteus x michahellis, and maybe this is also the most likely option for black K.B. It may explain the straw yellow legs, 8,5 greytone on upperparts, relatively much white in wing-tip and lack of red on the upper mandible. Also, looking closer at the legs it appears the legs are indeed yellowish, but feet seem to be more pinkish.
Ringer: Roland-Jan Buijs / Buijs Eco Consult.
Measurements & Photography: Roland-Jan Buijs / Buijs Eco Consult & Jeroen Nagtegaal / Hogeschool Larenstein.
Date: May 28 2013.
GREY TONE:
In the Netherlands, Herring Gull upper-parts is clearly paler than upper-parts of Lesser Black-backed Gulls, without any overlap in grey tone. The modal grey tone for the Herring Gulls sampled was 5 (range 3-7) and for Lesser Black backed Gull 11 (range 8-15). Samples are from the Moerdijk colony 2005 & 2006, sample size in Herring Gull: n = 292 and Lesser Black-backed Gull: n = 888. Measurements based on Agfa Grey Scale 0-20.
Grey tone of 8,5 in black K.B rules out typical Larus argentatus argenteus Herring Gull, breeding in the Netherlands, and also a deep coral red orbital ring and red gape is extremely rare (<0,5%) in breeding Herring Gull the Netherlands.
ORBITAL RING & GAPE:
Almost all Herring Gulls showed orange orbital rings (94%), with only 18 birds having yellow and one bird (HG NLA 5.363.004) a red orbital ring. Coral red is 'the classic' colour for Lesser Black-backed Gulls. Four Lesser Black-backed Gulls scored orange (LBBG yS8, y13, oC9, oTX), with all other individuals having red orbital rings. Sample for Herring: 284, and sample Lesser Black-backed Gull: 919.
All single characteristics in black K.B could just fit in Dutch Lesser Black-Backed Gull Larus fuscus graellsii, but the combination of features is highly unlike to occur simultaneous in a single bird:
- pale grey upper-parts (graellsii upperpart < grey 9,0 = 0,23%, n=888)
- no red nor black on upper mandible (graellsii no red on upper mandible = 39%), (graellsii no black on upper mandible = 19%). (graellsii no black on lower mandible = 32%)
- 6 primaries with sub-terminal black (graellsii primaries with sub-terminal black < 7 = 23%, n=931 in all breeding birds, n=869 in 5+CY birds / full adults)
- much white in P10 wing-tip. (graellsii no sub-terminal black or broken band on P10 = 17,5%, n=931)
- no black on primary coverts. (graellsii no black on coverts = 24%)
'Straw yellow' legs can be found in adult Larus fuscus graellsii, but saturated yellow legs are by far more common (no %).
Given the low %'s of occurrence of single features, and the low probability they occur simultaneously in a single graellsii bird (though some feature may correlate, like wing-tip pattern), the possibility this bird black K.B may be hybrid is real.
Then, speculation starts about parentage. This really is only speculation, as we know from ringed birds some offsprings don't show much similarity to any of the parents. Anyhow, michahellis x graellsii (several, about 30, mixed pairs annually in the Netherlands) would probably have rich yellow legs, red on upper mandible, not this much white on P10 tip, and also not such a long grey tongue on P7-P8 (grey running far down to feather tip, leaving only a narrow medial band). Also in this hybrid option, grey tone may be expected slightly darker.
Probably argenteus is involved, which has been expected to hybridise with graellsii in the past, but nowadays, with large populations of both species, hybridisation doesn't seem to occur anymore (at least, it is not documented over the last years as far as I know). Evidence of occurrence is green E433, hybrid pullus ringed on June 29 1995. This is different for argenteus x michahellis, and maybe this is also the most likely option for black K.B. It may explain the straw yellow legs, 8,5 greytone on upperparts, relatively much white in wing-tip and lack of red on the upper mandible. Also, looking closer at the legs it appears the legs are indeed yellowish, but feet seem to be more pinkish.