Grey Headed Gulls at Bonza Bay
Since the 1 January 2008 until 16 March 2017, small gulls have been observed at Bonza Bay on 32 occasions, which is 1% of the 2486 days when observations have been made. Those 32 records have occurred in ten months of the year, with a peak in May, but none were seen in April or October. The birds occurred in groups of one to 13, with a mean of three. Only one group was observed on successive days: a group of two birds present at Bonza Bay for four days in May 2009. However the groups of eight birds seen by Colin Levey, Phil Whittington and others at Nahoon estuary in November and December 2016 and in January 2017 and at Quinera Lagoon in February 2017 may relate to the same eight individuals. The small gulls observed at Bonza Bay were considered to be Grey-headed with the possible exception of the record discussed below.
On the 12 January 2011 at Bonza Bay a gull was tentatively identified by its small size as a Sabine's Gull. The bird was a juvenile and estimated to be one-third the size of an adjacent Kelp Gull. Its head was grey extending down the nape to the back and wings and its rump and upper tail were white, with a dark tip to the tail. The underparts were white. However none of those features are diagnostic of Sabine's Gull. Most of the small gulls seen were either adults in non-breeding plumage with a pale eye and dark red bill or sub-adults with a dark eye and a black-tipped yellow bill. Only two birds, which were amongst the eight seen on the 18th May 2009, had grey heads typical of adult Grey-headed Gulls in breeding plumage. Of 13 birds seen on the 21 February 2017, two thirds were adults and one-third sub-adults.
Whittington, P.A. 2014. Tips on identification of gulls in the Eastern Cape. Bee-eater 65(2): 50–53