Separating first winter Thayer's Gull from "Olympic" Gull

First year Olympic Gull and Thayer's Gull. Which is which? Forest Grove, Oregon, 23 March 2011 by Greg Gillson.

 

Right here in the Pacific Northwest we have one of the most confusing arrays of winter gulls in the world.

As if the 13 regular gull species weren't enough, we have numerous rarities and hybrids. In fact, in many locations on the Oregon and Washington coast, the hybrids between Western and Glaucous-winged Gull may be more common than the pure parent species. But we also have hybrids between Herring and Glaucous-winged, Herring and Glaucous, and Glaucous and Glaucous-winged!

The larger gulls take 4 years to reach adult plumage and change appearance twice each year as they do so. No wonder many birders never get comfortable identifying immature gulls--truly one of the more difficult topics of bird identification!

Olympic Gull
Western Gulls breed along the Washington coastline southward. Glaucous-winged Gulls breed from the central Oregon coast northward. Thus, their breeding ranges overlap for about 200 miles, centered at the mouth of the Columbia River. In this area of overlap there is considerable hybridization. Due to backcrosses, there is complete clinal variation from one end of the spectrum to the other. South of the Columbia River birds looking more like Western Gulls become more common. To the north, gulls that appear more like Glaucous-winged Gulls become more prevalent. This swarm of Western, Glaucous-winged, and hybrid Western x Glaucous-winged gulls is called the "Olympic Gull."

In winter, these coastal breeding hybrid gulls are found also inland in the Puget Sound and the Willamette Valley, and south along the coast regularly to at least San Francisco. Pure Western Gulls are rare inland; most adult "Western Gulls" reported inland show some evidence of past hybridization if you look closely at winter head streaking and intensity of black in the wingtips.

Hybrids, especially those tending toward Glaucous-winged Gulls in appearance, are easily confused with Thayer's Gulls. This post discusses these birds in the first year only. However structural features are consistent across various age groups.

First, correctly age the gull by looking at the back
First year gulls are rather brown-barred throughout. In the second year the upper back feathers become smooth gray similar to the adult coloration. Thus, on first year gulls the back is barred brownish. Most first year gulls have blackish bills and pink legs, so the color of these important adult ID field marks are of little to no use during the first year or two.

Look at the size and shape of the bill
Because there is so much plumage variation with hybrids, look next at the bill. Western Gulls and Glaucous-winged Gulls (and, thus, hybrids between the two species) have very large, thick bills. There is considerable size variation between the sexes (males are larger) but, even so, the bills are thicker than all regular Pacific NW gulls, and average longer than all gulls except the largest Glaucous Gulls. The bills are widest on the gonys. This is the point on the lower mandible where the right and left halves fuse together and angle up sharply to the bill tip, as shown on the adult Glaucous-winged Gull head photo, below.

The bills of Thayer's Gulls are shorter and thinner than the Olympic Gull. The female Thayer's Gull has an especially small bill, often described as "petite." The angle of the gonys is not as sharp as the Olympic Gull--the lower mandible of Thayer's Gull appears straighter.



Look at the primary/tertial/rest-of-wing contrast
Now turn your attention to the other end of the gull. It is important to be able to identify correctly the back, the scapulars, wing coverts, secondaries, tertials, primaries, and tail.

In the photo below, the tertials, primaries, and tail are identified. Most first year gulls have back, scapulars, wing coverts and secondaries very similar in color and pattern, as below. It is the contrast (or lack thereof) between the primaries, tertials, and the rest of the folded wing, that provides the final clues to reaching an accurate identification.



Most of the larger white-headed gulls in first winter plumage (Mew, Ring-billed, California, Herring, Western) have blackish primaries and tertials, contrasting with the rest of the wing which is barred brownish and pale.

Pure Glaucous-winged Gulls have matching colors to the primaries, tertials, and barring of the rest of the wing on a first year bird. Often the color is a very pale gray-brown.

First year Thayer's Gulls are the only pure gulls that show medium-brown primaries, contrasting with a paler wing panel.

Hybrids--the Olympic Gulls--show a similar pattern to pure Glaucous-wingeds. There will be little contrast between the various wing feathers, but they are often much darker brown than pure Glaucous-winged Gulls, especially on the primaries.

If the primaries on a first year gull are brown, you are probably looking at a Glaucous-winged hybrid (most-likely an Olympic Gull) or a Thayer's Gull.

The key is in the contrast of the primaries, tertials, and rest of wing. These match in coloration on Glaucous-winged hybrids. Thayer's Gulls show a unique difference--three shades. The tertials are darker than the secondaries and wing coverts, and the primaries are darker than the tertials.

Are you ready to identify these gulls? What do you see on the next photo? Big and thick bill or smaller and slight? Do the primaries, tertials, and rest-of-wing all contrast strongly with each other and get paler with each feather group?

Hybrid Western x Glaucous-winged Gull ("Olympic Gull"), Forest Grove, Oregon, 7 February 2009 by Greg Gillson.

 

How about the next photo? Same questions. Big and thick bill or smaller and slight? Do the primaries, tertials, and rest-of-wing all contrast strongly with each other and get paler with each feather group?

Thayer's Gull, Portland, Oregon, 19 February 2011 by Greg Gillson.

 

Now you are ready to go back to the top photo and puzzle it out.

Mystery Gull

Mystery Gull. 26 June 2011 at Newport, Oregon by Chet Conklin.

 

Every summer a few very white gulls--similar to the one photographed above and sent to me by Chet Conklin--show up and really confuse birders. [Thank you, Chet, for allowing me to use your photos.]

Gulls like this with a bit more pink on the bill are often reported as first-year Glaucous Gulls on the West Coast in summer. But with the dark bill, one may be tempted to match this with an illustration of a juvenile Iceland Gull!

This is not a Glaucous Gull nor is it an Iceland Gull. Here is why.

Ignore the bright white feather color for a minute and look at other field marks, especially shape. This fairly stocky gull has wings that extend barely beyond the tail (it is “short-winged”). The eye is dark, but I do see a paler iris than pupil in one photo. The forehead is rather flat and sloping. Legs and feet are pink. The bill is nearly entirely black, with pink gape (the corners of the mouth on the face) and a bit of paleness at the base of the lower mandible. The bill is heavy and thick, “swollen” at the gonys (where the red spot would be on the lower mandible, if this was an adult of one of the larger species of gulls). The bill is strongly hooked.

The body shape of Iceland Gull is long and thin, with long wings. The bill is small and petite on Iceland Gull, and doesn’t show such a strong hook. The head should be quite round. The Iceland Gull as a whole is “petite.” The bird in the photo is stocky.

The body shape is all right for Glaucous Gull, but the bill is wrong. The bill of Glaucous Gull is stout, but not overly wide at the gonys. The bill shape is not a good fit. More importantly, the bill of young Glaucous Gull is 3/4 to 4/5 pink with the outer 1/4 (or 1/5) of the bill sharply black.



Now go back to the color. Only the Ivory Gull is this all-over-white in normal plumage. Other white gulls will show darker gray or brown bars on the body plumage. So this gull is not in “normal” plumage.

One condition that could explain the white coloration is leucism, a condition where the feathers are unnaturally pale or even white. This is not albinism, as that condition is the lack of all color, which would include pale legs and bill, with an eye with a colorless iris—blood in the vessels making the eye appear pink. I learned recently it was incorrect to call a bird a “partial albino.” But this bird is not leucistic, either, as a close examination of the feathers will reveal.

Take a look at the top photo. Click it to bring up a larger view. Can you make out any nice-looking individual feathers?

Not really. The feathers are shaggy and many look more like hair. This bird is extremely worn. The feather vanes are mostly worn away and only the feather shafts remain. White feathers are weaker than dark feathers; they wear away more quickly. Even though this bird did get new head and breast feathers in April or May, this bird is in desperate need of new feathers again. But it’s not going to get any soon. Gulls go through a complete molt of all their feathers in fall, September through November.

Because this bird has a mostly black bill, we can say it was hatched 1 year ago, probably June 2010. After a few weeks in a downy state, it grew its first set of feathers. But juvenile birds do NOT turn around and molt right away again in the fall. Thus it keeps its first feathers (wing and tail) for over a year. (Body feathers—head, neck, breast, belly, back—are replaced also in spring.) Such one-year old gulls can become very worn and sun-bleached by summer—especially the wings and tail. Thus, this is a very worn and bleached gull.

Now that we know this vital piece of information we can go on to ask: "what species is this?" Well, the angled head and “monster” bill, as well as short wings and stocky body, point to the common West Coast gulls: Glaucous-winged Gull or Western Gull. Since the bird is so pale and worn—and paler feathers wear faster than dark feathers—we can say that this bird was originally quite pale. That makes this a first cycle Glaucous-winged Gull (some plumage descriptions of the past may call this a “first summer” plumage, in the sequence of downy, juvenile, first-winter, first-summer, second-winter, etc. until it becomes an adult in the 4th winter).

As noted earlier, many Glaucous-winged Gulls of this age have a much paler pink base to the bill (though uneven) and are reported as Glaucous Gulls.

There. More, I’m sure, than you ever wanted to know.

But in case you're not satiated yet, here is more:

A previous post on Glaucous-winged Gulls.

My pBase photo album images of Glaucous-winged Gulls.

Glaucous-winged Gull

Glaucous-winged Gull, at sea off Newport, Oregon on 6 March 2010 by Greg Gillson.

 

In the 1953 book, Birds of Washington State, Jewett, Taylor, Shaw, and Aldrich described the southern edge of the breeding range of Glaucous-winged Gull as Destruction Island, Washington, nearly due west of Mt. Olympus on the Olympic Peninsula. Likewise, that island about 4 miles offshore was the northern edge of the breeding range of the much darker Western Gull.

Today the situation is much different--for the Glaucous-winged Gull, anyway. This pale gray gull, with upper wingtips concolorous (in all plumages) with the rest of the upper wing and back, now breeds south to the central Oregon coast.

The range expansion created a new population dynamic. In the 200 miles where the two ranges now overlap, Glaucous-winged and Western Gulls hybridize extensively. The fertile crosses and back-crosses span the entire spectrum from looking quite pale like Glaucous-winged Gull to very dark like Western Gulls. The hybrid swarm is often referred to by birders in the Pacific NW as "Olympic Gulls." In fact, many birders along the central Washington coast do not try to differentiate them, even when surveying seabirds.

In winter, Glaucous-winged and hybrid gulls are common along the coastline south to San Francisco or farther, in the Puget Sound area, and inland in the larger towns west of the Cascades, and increasingly as vagrants across North America. In contrast, "pure-looking" Western Gulls are rare away from the immediate coast.

As with most larger gulls, they are omnivorous, eating anything they can swallow. They are common in garbage dumps and parking lots of fast-food establishments.