Grey Headed Gulls at Bonza Bay

Posted on 17 March by Carl Vernon in Birds

Grey Headed Gulls at Bonza Bay
GREY HEADED GULLS AT BONZA BAY
 
In South Africa, five species of small gulls have been recorded with some degree of regularity: Franklin's, Grey-headed, Hartlaub's, Black-headed and Sabine's. Two of them, the Grey-headed and Sabine's are recorded on the 2008 Checklist of Birds of the Border. Subsequent to the Checklist a single Franklin's Gull was seen at Eastern Beach on the 13 May 2009. The fourth species Hartlaub's Gull, a bird of the Western Cape, is not known to occur east of the Coega River, although there has been a recent record of one in Durban Bay (T. Hardaker in litt.).
 
The identification of small gulls is difficult because of similarities in their adult and juvenile plumage. This is compounded by the fact that the Grey-headed and Hartlaub's gulls inter-breed. According to Phil Whittington, they do so in the Swartkops valley at Port Elizabeth. ”Separating Hartlaub’s and Grey-headed x Hartlaub's hybrids from Grey-headed is not always straight-forward when dealing with anything other than breeding plumaged adults” (P. Whittington in litt.). Adult Hartlaub's Gulls in breeding plumage have a plain white head with a lilac line around the rear of the ear coverts. Hartlaub's generally has a darker red bill than Grey-headed and normally has a dark iris, whereas adult Grey-headed has a pale iris (Whittington 2014). However, immature Grey-headed Gulls have a dark brown iris and some apparent Hartlaub's have a pale iris, possibly an indication of hybridisation. Juveniles and immatures of both species can have a dark iris and black spot at the rear of the ear coverts, but Hartlaub's lacks the dark band at the tip of the tail shown by juvenile/immature Grey-headed Gulls (Whittington 2014).

 

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.

References 

Whittington, P.A. 2014. Tips on identification of gulls in the Eastern Cape. Bee-eater 65(2): 50–53




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