This morning a Slaty-backed Gull was found at a dump half an hour from my office so I trucked over there in the rain to find that it had flown shortly after it was found, and hadn't been seen since. I spent a couple hours there and was able to get some nice looks at Iceland Gulls and a probable Nelson's Gull (Herring Gull x Glaucous Gull hybrid). Also nice to see several Great Cormorants roosting on a buoy in the Delaware River south of the Bristol Bridge.
I've missed Slaty-backed a couple times in the past--including a bird I had in Texas that I was pretty sure was this species at Bolivar Flats in April 1995, but a dog and jogger scared it away before I could be see all of the necessary fieldmarks.
Perhaps this bird will stick around, but there are tens of thousands of gulls down at the Tulleytown Dump, the birds move around all the time, and it can be tough to relocate these beasts!