23rd February – Possible Slaty-backed Gull (?), Hartford County, CT

A small band of CT birders visited the Windsor landfill to look for a couple of potentially “good” gulls. Although gull numbers were low, there was a nice 2nd-cycle Kumlien’s Gull and the putative Slaty-backed “thingy” amongst them. Found initially by local birder Mark Szantyr, it had attracted attention during the week. Although Nick and I looked at it, we seemed suitably not bowled over since it seemed duller and more Herring Gull-like in certain lights and poses. However, there were definitely some good Slaty-backed traits, but the identification issue is clouded by the unfamiliarity with this taxon, especially in this plumage. When reviewing the images later, Nick and I became a little more convinced about it looking more Slaty-backed-like than initially thought. In some pictures, there seems to be a hint of a “string of pearls” on the inner primaries and are those rear scapulars good for Slaty-backed?. Comments welcome either way. All photos by moi…

Peter Adriaens, a Belgian birder whose opinion I respect on identification matters, especially gulls commented as follows:

“My impression was and still is that this bird’s plumage looks very similar to 1c Slaty-backed indeed, and it may well be one. 

     The simple pattern of tertials and wing coverts looks good, the latter also being very pale. White edges to the tertials, all the way to the greater coverts.

The pattern of the primaries seems ok: pale tongues outwards to P9, and the inner primaries have fairly dull bases and whitish distal area.

    In many birds, the bases are a bit darker brown (almost matching the colour of the outer primaries),

and the contrast with the whitish distal area more pronounced, but it is certainly still within variation. 

The uppertail coverts lack the strongly barred pattern of smithsonianus, and look good for Slaty-backed. 

Bill looks a bit stouter than in average smithsonianus.

 

However, there are a few issues that need to be addressed:

– The tail shows rather striking dark barring on the outer webs of the outermost tail feathers, right up to the very base.

This is odd for 1c Slaty-backed; they usually have an all-dark tail. Some birds have pale bases to outer tail feathers, but these are usually only poorly marked

or even completely unmarked. In fact, the only bird I could find among my photos that closely matched this kind of tail pattern is one that showed mixed characters

of both Slaty-backed and Vega Gull… I have (temporarily) uploaded some images of Slaty-backed Gulls with some degree of dense dark barring on outer tail feathers here:

http://users.telenet.be/peteradriaens/slaty/

As you can see, they approach the pattern seen in the Connecticut bird, but the latter is more extreme still, and a step further toward the tail pattern commonly seen in smithsonianus.

– Pattern of wingcoverts: Especially in late winter, 1c Slaty-backed Gulls often have (very) pale greater coverts that contrast with darker and more strongly pattern median and lesser coverts.

In the Connecticut bird, it is the lesser coverts that are palest, even paler than the greater coverts. I could find no birds matching this ‘reverse’ pattern among my pictures.

– Shape: Many Slaty-backed Gulls show typically big, “inflated” body with angular, goose-like vent and short wing projection. Some are slimmer and more elongated though, as you can see in the link to my webspace. So, on the one hand, I think the body shape of the Connecticut bird is within variation, but on the other hand it could have been more convincingly different from American HG.

– Leg colour: The vast majority of 1c Slaty-backed Gulls show bright pink legs, often with dark shins. The leg colour of the Connecticut bird seems a bit paler, and not too different from AHGU (?)

Furthermore, the undertail coverts of the Connecticut bird look rather extensively barred. They are usually more liberally spotted in 1c Slaty-backed, but there are birds with more of a barred pattern (inviting confusion with AHGU).

 

All in all, I feel the Connecticut bird may be a variant Slaty-backed Gull; it certainly looks so similar that it would be worrying if it is something else entirely!

However, it does not look entirely typical, and I am unable to exclude something like a Slaty-backed x Vega Gull hybrid, or perhaps even a very unusual smithsonianus with certainty.

There may also be Glaucous-winged x AHGU hybrids to worry about, reinforcing the importance of the tail and wing covert pattern.”

 

Hopefully this is helpful in some way…

Peter

Several other experienced birders have weighed in but overall, such a beast out of context, with anomalous plumage for both SBGU and AMHEGU, seems destined for the “in limbo” bin.  An interesting bird that, if nothing else, has been a primer for what to look for on putative first-cycle SBGUs.

 

Tags: Slaty-backed Gull