An Unidentified, Probably Hybrid, Gull at Minsmere

A N UNIDENTIFIED, PROBABLY HYBRID, GULL AT MINSMERE H. E.

AXELL

ON 16th May, 1972, J. Warham, C. Murphy, and I were in the West Hide at the R.S.P.B, reserve at Minsmere, Suffolk, watching the evening build-up of the roost of non-breeding gulls on T h e Scrape. At 7.20 p.m. we saw a bird Coming in low with blackheaded gulls Larus ridibundus which gave the astonishing impression of being an adult kittiwake Rissa tridactyla with the wholly black head of an adult Mediterranean gull Larus melanocephalus. As it flew in a leisurely way across the water it appeared to have the distinct black triangle at the wing tip, the black hood extended further down the back of the head than in a blackheaded gull while the rest of the wing and upperparts were pale grey; the tail was white and unforked.

T h e bird landed on an open clay bank among roosting blackheaded gulls. It was then some 250 yards from us, but in the good evening light it could be well studied through 10 X binoculars and a telescope at up to 60 X. Standing, it appeared to be as large or a little larger than the black-headed gulls around it. Its wholly black head was blacker than the other gulls alongside and was quite like the head of a Mediterranean gull; this feature made it more prominent in the group.

My wife (JMA) and assistant-warden, P. J. Makepeace, then joined us and the following further details were agreed by all observers. T h e bill and legs were a dark but bright red and this colour could still be seen when the light was fading and the colour of the black-headed gulls' bills and feet could not be made out.

T h e breast was suffused with pale pink but this colour was visible

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only while the light was good. The rest of the underparts were pure white. Occasionally the stränge gull was forced to move a few feet by hostile actions of the black-headed gulls. When the bird raised its wings, a narrow white fringe to the wing tips and a narrow white line between the black triangle and the grey of the wings could be seen. The grey of the rest of the wing and the mantle was rather paler and bluer than the accompanying blackheaded gulls. There was a narrow, complete white ring round the eye. It was watched until dark and was not seen again.

The bird had the main plumage characters, i.e., wholly black hood, black wing tips, and red bill and legs of Franklin's gull Larus pipixcan which breeds in the prairies of central North America and winters on the Gulf coast and the Pacific coast of South America. Franklin's, however, is rather smaller than black-headed gull; it has a broader and conspicuous white band between the black of the wing tip and the grey of the rest of the wing and this white band extends along the trailing edge; it has a broken white eye ring and the grey of the upperparts is darker.

Details of the Minsmere bird were sent to the Rare Birds Committee of British Birds who suggested it was a hybrid. Of the possible permutations, Mediterranean gull X common gull might produce such a bird as we saw and it is understood that interbreeding of these two species has been recorded in the Baltic.

H. E. Axell, M.B.E., Minsmere Reserve R.S.P.B., Saxmundham, 1P17 3BY, Suffolk.

Westleton,