I saw a very interesting gull today.  I first saw it while I was working at home, on the phone, and noticed a dark-backed gull with some Ringers.  They were resting on a mud flat at low tide, on the Anne Arundel side of Jug Bay.  I usually look carefully at these birds, but since I was working at home and paying attention to the phone conversation, I didn't care when I first noticed it.  I assumed it was a Lesser Black-backed based on the slatish color of its black back, and smallish size.  They are uncommon here but seen occasionally through the winter.  I have seen one twice here so far in 2012.  About 15-20 minutes later when I finished the call, I promptly had another call but took a casual look at the gulls again.  This time I had a better view.  It was still among the same group of Ringers (all adults, more or less), but there were a couple of Herring Gulls now too.  The dark-backed bird was clearly much larger than the Ringers, but seemed about the same size as the 2 Herrings which it was near now.

However, the light was getting better (less shimmer) and in my scope I noticed its feet were not yellow; I could see their color was pinkish.  Hmm, must be a Great Black-back I guessed, but this seemed odd since Great BBs are much larger and the size difference is usually very noticeable.  And the black back was not coal black.  But I still did not think much of it, as I was paying attention to the call again.  So I wrote it off as a Great BB that I was somehow thrown off by on the size and color.  It appeared to be smaller than what I expected and seemed a very light shade of black, but whatever!

Ten minutes later I finished that call, and came back.  I was not even intent on looking at the bird further, and there were many more gulls loafing on Jug Bay now.  I was hoping for a white-winged gull, but when I came across the dark-backed gull again, I quickly realized something just didn't seem right and I stopped looking at everything else.  Light was now excellent, but when I studied the bird I was puzzled.  It's back color was a medium (dark) slate gray, not coal black like a GBB should be, and at 4:45 pm, the strong afternoon light came at a low angle, giving good colors.  I carefully compared its size with the adjacent Ringers and Herrings, and it clearly was similar in size to the Herrings, too small for GBB.  Further, I could see its head and neck were very smudged, and its chest showed a bit as well.  The smudging was light colored, but very evident in my scope.  It seemed like way too much for a Great BB and even for a Lesser BB (which has more than GBBs), and resembled an adult winter Herring gull's smudging.

Then it raised its wings and held both of them straight up.  I was immediately drawn to the very broad crisp white trailing edge of its wings, which was not evident while it was at rest.  Of course Black-backs have this too, but it seemed to be clearly much broader than what I was expecting, and it seemed to be along its entire wing length.

Then the possibility dawned on me and I hate to even say it, but this may have been an adult Slaty-backed.  I have never seen one but knew I was not recognizing what I was looking at, and ran in to get my phone to see if I could try any digiscope shots.  When I came back out only a couple minutes later, nearly all the gulls had moved (argh!) and an adult eagle was sitting nearby instead.  I could see the gulls had gone further down Jug Bay.

It was now after 5 and good light (for photos) was going to fade quickly.  I moved to get a better view and tried a quick scan with my scope at the river, and found there were way more gulls further down on Jug Bay than what I previously realized.  The majority were Herrings, but I could not locate the dark-backed gull among the crowd.  Regardless, they were too distant now for any hope of a recognizable photo even if I did see it.  Darn!

I have since studied my gull guides this evening, and after trying to rule it out, am still open to the feasibility of it being a Slaty-backed.  I realize this would be exceptionally rare and hesitated to even post this, but I am convinced it warrants mention.  I did not notice any "string of pearls" but at the distance I don't know if I would have noticed it anyway.  I don't know if this is even a good field mark.  Seems like you would need a photo, or long view of its extended wing at close range.  Does anyone have a suggestion for diagnostic field marks to look for?

I am working in the office tomorrow and won't be around Jug Bay, but I have Friday off and will be on the lookout for this bird.  If I find it and confirm its id as neither Great or Lesser Black-backed, I will post asap!

Cheers-
Jeff Shenot
Croom MD

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