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Sunday, December 14, 2014

The Gull Gullibility Trap

[Lake St. Clair Metropark, MI. Nov 2014]

No seasoned observer has escaped the birding shame that Gulls bring through misidentification. The myriad plumage variations based on age and seasonality coupled with the similar features of some species (not to mention hybridization) lull gullible birders into an easy misidentification trap that only much experience in the field, and much gnashing of teeth over Field Guide illustrations, can hope to thwart.

In this post, we look at some Gull species and explore what some of these identification challenges might, or might not, be.

A dainty gull seen in the Fall with pink legs and a thin bill could only mean one thing: Bonaparte's Gull.

Bonaparte's Gull   

Bonaparte's Gull seen at Lake St. Clair
The only other, somewhat common, similarly sized gull with a delicate bill is the Mew Gull:

Mew Gull seen in Vancouver, BC. August.2010.

Thankfully, the yellow of the legs and bill, as well as the head markings, are obviously distinctive enough to avoid any possible confusion with the Bonaparte's.

Here's another gull with reddish legs:

Silver Gull. Victoria, Australia. Feb 2012.
There have been only two records of Silver Gull in the US and both records were discounted on account of a high probability that the gulls in question were escapees; thus, Bonaparte's Gull is unlikely to pose much of an identification conundrum with the Silver Gull!

Ring-billed Gull seen at Lake St. Clair
Ring-billed Gull is a readily identifiable species on account of its yellow legs and distinctively black-ringed bill.

Ring-billed Gull, Juvenile.

Compared with California Gull (below), both species appear superficially similar.
California Gull seen at Laguna Beach. CA. April 2011.
However, note that California Gull has a small red spot behind the black tip of the bill. Indeed, paying attention to the bill of a gull is a key technique in gull identification. And, many gulls have bills with a dark tip -- such as Heermann's Gull:

Heermann's Gull seen at La Jolla. CA. Apr 2011.
Fortunately, Heermann's Gull light grey color scheme (the head turns white in alternate plumage), dark legs and red bill make it unmistakable. It is also highly range restricted to the Pacific coast of Mexico and the US thus making it extremely improbable that this gull could be confused with any other species.

Herring Gull seen at Lake St. Clair

The Herring Gull (above), unlike Heermann's, is widespread and its overall appearance doesn't seem terribly different from the Western Gull below:

Western Gull seen in California.
However, closer inspection shows that Herring's grey mantle is lighter; Western's bill is bigger and stouter at the tip and brighter in color than the pale yellow of the Herring's.

Compare the Herring Gull again -- but this time with Glaucous-winged Gull:

Glaucous-winged Gull. Vancouver, Aug 2011
A lot of similarities arise but note that Glaucous-winged is paler overall and that there is no black in the plumage unlike the Herring Gull.

Not all avian families are as cooperative as Wood Warblers in identification -- Gulls don't come in easily distinguishable combinations of color, facial markings and signature songs. Nevertheless, Gulls, in their subtly pale colors and bright bills, offer birders an opportunity to sharpen their identification skills and deepen their expertise about a uniquely specialized, and successful, family of birds.

1 comment:

France Paulsen said...

Thanks for this post, it is timely as I am seeing more and more gulls during the winter time. I also find it quite challenging and that makes it fun.