Comox Valley Naturalists Society

December, 2004
Frank Hovenden

If you wish to irk a birder, try calling those large white birds that are perpetually on the prowl for an easy meal, a “sea gull”. Vancouver Island abounds in gulls. We have mew gulls, glaucous-winged gulls and western gulls. Flocks of Bonaparte’s gulls fly through every spring heading north, and again in the fall heading south. Occasionally we have California gulls, herring gulls and sometimes in winter a Thayers gull will visit. Among these many birds nary a “sea gull” will be found. The Audubon’s Master Guide to Birding lists 23 different gulls none of which is called a “sea gull”.

Gulls are notoriously difficult to identify and even the most seasoned birders find themselves second-guessing when it comes to gull ID. It starts easily enough with large gulls like the glaucous-winged, (our most common local gull), easily separated from the smaller gulls like the mew gull. The ID gets considerably more difficult from there on.

The first hurdle to surmount is to figure how old the gull is. The large gulls take four years to mature, while small gulls like our mew gull take three years. In each of these years they have a different appearance although not much difference in size. While the plumage generally becomes lighter with age it is not the only characteristic to change dramatically. In the glaucous-winged gull the bill on a 1st year bird is all black. It changes to a black tip by the third winter, while the four-year-old adult has a yellow bill with a red spot on the lower mandible. Of course most of these changes are gradual so there will be a full range of variability between any two phases. If this hasn’t scared you off gull ID, bear with me a while longer.

When two closely related species interbreed their offspring are known as hybrids. These generally have the intermediate character of both parents. The glaucous-winged gull has a light grey mantle (the mantle being the evenly coloured upper parts in a gull which includes most of its back and wing surface).

Slightly south of here in Washington State the most common large gull is the western gull, with a dark grey mantle. The glaucous- winged and the western gulls freely hybridize producing birds with a medium grey mantle. If you had all three adult birds in a police line-up the differences would be slight. On a grey winter day with a southeaster blowing and your binoculars fogging up I challenge the most experienced birder to separate these three with any degree of certainty.

The gull challenge does not end there. The most widespread large gull in North America is the herring gull. This bird also hybridizes with the glaucous-winged gull producing hybrid offspring of an intermediate nature and more challenges.

You may wonder why there are so many similar gulls? The gulls are an example of evolutionary divergence. It is believed that the gulls had a common ancestor. The many species we now see are adapting to their chosen environments. If we should be around for another 100,000 years we would probably find that the individual species had become more distinct as they evolved.

For those of you determined to master gull ID there are some excellent websites dedicated to this task, such as the University of Puget Sound, which offers on-line quizzes. Try typing in gull identification into your search engine. What waits is a whole birding cult dedicating to identifying the gulls.

For those who have given up hope of ever identifying a gull I offer the following advice. If it is large (length 26”), call it a glaucous-winged gull. You will be right 90% of the time. If it is a small bird (length 16”) call it a mew gull. If you can’t decide if it is large or small hold your nose and call it seagull and you will be no more wrong than the rest of us!

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