Wednesday, 9 March 2016

Black-headed Gull x Mediterranean Gull

third-summer (4th calendar-year) Black-headed Gull x Mediterranean Gull hybrid, Christopher Cadbury Reserve, Upton Warren (Worcestershire, UK), 12th March 2017 - copyright John Oates
(photo ID: 3173)


A regularly-returning bird in Worcestershire (central England) has allowed us to see how one example of this hybrid progresses from first-year plumage through to adulthood.  In the following photo when it was in its first summer (second calendar-year) the jet black head and contrasting white eye-crescents recall Mediterranean Gull but the fine bill is more like that of Black-headed Gull.  The shape of the black hood is perhaps intermediate, but certainly doesn't curve up at the rear like it does on Black-headed Gull.  The rather thin-looking reddish legs are more like Black-headed Gull.

Black-headed Gull x Mediterranean Gull hybrid, Christopher Cadbury Reserve, Upton Warren (Worcestershire, UK), 21st June 2015 - copyright John Oates
(photo ID: 2736)


John's flight shot of this first-summer bird (below) shows a wing pattern that is somewhat intermediate between the two species, though perhaps closest to Mediterranean Gull.  There is too much black on the wing-tip for Black-headed Gull, and the grey inner primaries and outer primary coverts are like Mediterranean Gull, yet the band of brown coverts across the middle of the forewing reminds me more of Black-headed Gull.

 Black-headed Gull x Mediterranean Gull hybrid (same bird as in photo ID 2736 above), Christopher Cadbury Reserve, Upton Warren (Worcestershire, UK), 21st June 2015 - copyright John Oates
(photo ID: 2737)


John tells us that the same bird had been at Marsh Lane in April 2015.  What is presumably the same bird returned to Upton Warren in 2016.  As before the blackness of the head recalls Mediterranean Gull, but the shape of the black, with white curving up at the rear, is like on Black-headed Gull.  The wing pattern is perhaps closest to Black-headed Gull with black tips to the primaries, thin black line on outer edge of outer primary and white wedge on outer primaries contrasting with greyer inner primaries.  But there is more black on the tips, which is apparent on the closed wing too, and a long black spot on the outer web of the second outermost primary.



 Black-headed Gull x Mediterranean Gull hybrid (presumed same bird as in photo IDs 2736-2737 above), Upton Warren (Worcestershire, UK), 26th March 2016 - copyright Craig Reed
(photo IDs: 2759-2761)





Black-headed Gull x Mediterranean Gull hybrid (presumed same bird as in photo IDs 2736-2737 and 2759-2761 above), Upton Warren Nature Reserve (Worcestershire, UK), 24th April 2016 - copyright John Oates
(photo IDs: 2788-2791)


It has been seen again in 2017, now in its fourth calendar-year. The wonderful photo at the top of this page was taken at the same time as this next one and both show the distinctive wing-pattern well.

Black-headed Gull x Mediterranean Gull hybrid (presumed same bird as in photo IDs 2736-2737, 2759-2761 and 2788-2791 above), Christopher Cadbury Reserve, Upton Warren (Worcestershire, UK), 12th March 2017 - copyright John Oates
(photo ID: 3174)


There were quite a few reports of this type of hybrid in the UK during the 90s when Mediterranean Gull was spreading in to the UK as a breeding bird.  More recently, as Mediterrean Gull becomes more established as a breeding bird, I get the impression that records have become scarcer again, a pattern that is typically seen when a recent coloniser becomes established.



Black-headed Gull Chroicocephalus ridibundus
Mediterranean Gull Larus melanocephalus

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