This small 2CY bird was found by Dick Newell, Richard Patient and Stuart Elsom. First seen rear on, it showed an all black tail, without white at the exposed bases of the outers, and with poor contrast against a boldy barred rump and upper tail-coverts. The whole head looked smooth chocolate-brown and the hind neck was darker. With its bi-coloured bill, consideration was given to American Herring Gull. When the bird turned around, we were startled to see that the breast and underparts were also smooth chocolate brown, though mottled. The under-tail coverts were also boldly barred (as can just be seen below), and in flight, Richard Patient caught sight of dark under-wing coverts.
This is one of the better candidates for smithsonanius that we have seen in Cambs, but, although it is possible for smithsonianus to show coverts and tertials like this, one would expect most smithsonianus to show much darker greater coverts, darker centred tertials and more densely barred under tail-coverts. Also, possibly the head should be whiter, contrasting with the underparts. This, in combination with the bird's small size and weak bill, means that it is almost certainly a Herring Gull.
Unfortunately, we lost the bird after taking an inadequate set of photographs.