Wednesday, 17 June 2015

Identifying the Gull by Steve Bright

Gulls are a family which I find really interesting so I was delighted when Julian sent me the images of the large Larus species he saw recently. Despite only having a limited time to view the bird he managed to get images with enough detail to lead to a confident ID. 

I am by no means an authority or expert on gull identification but I love to work through the process methodically.

My thought process on this gull was as follows:

  • It's clearly a large gull, excluding the small larids such as Laughing, Franklin', Bonaparte's, Black headed gull.
  • Its wing tips are black excluding the white winged species such as Iceland and Glaucous gull and grey winged gulls such as Glaucous-winged and Kumlien's gull.
  • The mantle colour is relatively pale excluding Lesser Black backed through to Greater Black backed gull.
  • It leaves the paler grey mantled gulls. For me the 3 main contenders were Yellow-legged, American Herring and Herring gull.
  • The wing tip pattern is often a critical identification feature in large gull diagnosis but there can be much variation within a species. Looking at the wing pattern here the amount of white on primary 10 seems too small for Yellow-legged gull. This, coupled with the amount of white on P9 tip being relatively large, effectively excludes this species.
  • This leaves the two Herring gull possibilities. There appears to a quite a large amount of black on the tips of primary 5 & 6 which looks good for American Herring gull.

During my research on this bird and being that I am from the UK, most of my literature, especially my main reference text - Gulls of Europe, Asia and North American by Klaus MallingOlsen and Hans Larsson - refers to this as a separate species. Several authorities on this side of the Atlantic, such as the Association of European Rarities Committees and British Ornithologists' Union recognise American Herring gull as a separate species (Larus smithsonianus) having been split from Herring gull (Larus argentatus) based on a report from 2007 (Sangster et al.  Taxonomic recommendations for British birds: Fourth report.  Ibis [DOI: 10.1111/j.1474-919X.2007.00758.x]) suggesting American herring gull should be moved into a different clade or lineage. That clade includes the East Siberian gull, Larus vegae, which occurs in northeast Asia.

However, American authorities such as the American Ornithologists' Union (AOU) and the American Birding Association (ABA) still consider it as a subspecies of Herring gull (Larus argentatus smithsonianus).

The 'smithsonianus' gull is distributed throughout North America with the breeding range in the north of the continent but the winter range extends south into Central America and the Caribbean.  Herring gull (Larus argentatus argentatus and argenteus) are confined to Northern Europe making the former much more likely on a Caribbean island.

Regardless of whether this is considered a separate species or part of the Herring gull species, this is a rare bird in Barbados and another great find.  

Steve Bright has been interested in birds since he was a child and has now been birding for over 20 years. He started to take birding seriously  during his first conservation expedition to Northern Cyprus. During the University of Glasgow's ongoing project monitoring breeding populations of green and loggerhead turtles he met likeminded bird obsessed students which spurred his interest further. Subsequent expeditions involved trips to the study the endemic Seychelles white-eye (Zosterops modestus), at the time considered one of the rarest birds in the world. During this trip he located a solitary osprey which was a national first. He subsequently coordinated expeditions to Ecuador and Kazakhstan in search of important bird areas supporting some of the World's most threatened bird species. Now very much a hobby, Steve continues to birdwatch whenever he can and has been lucky enough to visit many countries and has birded in all continents except Antarctica.