Simcoe County Bird and Nature Board.
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Re(1): Possible Great Black-backed x Herring Gull Hybrid -- Barrie Waterfront Posted on December 30, 2018 at 06:56:14 PM by Bob Bowles
Herring Gull x Great Black-backed Gull hybrids have increased in number since the first North American report hybrid dead specimen collected on January 10, 1959 at Staten Island, New York. Since then there are records from Kingston, Ontario on January 12, 1967, on the Niagara River on December 5, 1970 and November 22, 1971, and at Ottawa, Ontario on September 25, 1974. More records on the Niagara River in 1968 and 1969, Ottawa in 1972, 1973 and 1974 all in November. Since that time there have been many more confirmed reports in the Great Lakes area.
These hybrids could be mistaken for the paler rare of the Lesser Black-backed Gull, dark-mantled subspecies of the Great Black-backed Gull, Western Gull or even Slaty-backed Gull. This record interested me since there was a November report of this species in North Bay north of us and then two records of the species at a landfill southwest of here near Brampton.
The hybrid mantle colour of each should be a neutral gray. The primary pattern is variable but with a long subterminal (or terminal) white spot on P10 and a shorter (half as long) subterminal white spot on P9. The leg colour is whitish or very pale flesh pink. The eye-ring and iris colour are various shades of yellow. The streaking on the head and neck is variable but less intense and more restricted than winter plumaged Herring Gulls. Variations include no subterminal white spot on P9 and eye-ring colour dark to bright red and one with no head streaking.
The paler mantle, heavier bill, larger size, and eye-ring colour when yellow should eliminate Lesser Black-backed Gull. The darker mantle and large size also eliminates subspecies of Herring Gulls.
Herring Gulls have white fingernails on P5 to P 10 and a white window on P10. Great Black-backed Gulls have white fingernails on all primaries but longer on P9 and P10 but no white windows. Hybrids have white fingernails on P5 to P9 (or subterminal white spot) and extended white subterminal on P10.
Your bird shows heavier streaking on head and nape than Great Black-backed Gull but with a similar heavy bill with extreme gonydeal angle. Mantle shade is between Herring Gull and Great Black-backed Gull. Your bird shows white windows or mirrors or subterminal white marks on P9 and P10 like Herring, white fingernails on P5 to P10. The P10 white mirror is extended and about twice as long as the P9 white mirror which fits with the hybrid species. The leg colour of your bird is flesh pink to lead colour legs. The eye-ring and iris colour is yellow so these last two features fit with a hybrid Herring and Great Black-backed Gull . Given all these features that match a hybrid Herring Gull x Great Black-backed Gull, I feel there is no doubt that you are correct and this is a hybrid. You did an excellent job of capturing all the fine details like mantle colour, gull size, head and nape streaking, eye-ring and iris colour, and especially primarily wing fingernails and windows or mirror colour and shape in your excellent photographs.