A contingent of Ithaca birders made a trip to Sullivan County on 22 Feb 2002 in search of a reported Slaty-backed Gull (Larus schistisagus), a very rare visitor from Siberia. Seen the previous day, this sighting represented the second state record for the species (see Freer et al. 2002). A day-long search by a large number of birders produced nothing, and we went home somewhat disappointed. It turned out, though, that our adventure was not over.

On Saturday 23 Feb 2002, Steve Kelling, his passion for gulls heightened rather than quenched by the fruitless search of the previous day, decided to visit Seneca Meadows landfill, just north of Seneca Falls in Seneca County, NY. The landfill attracts a large number of winter gulls of numerous species, and already that season had produced multiple sightings of Glaucous Gull (L. hyperboreus), Iceland Gull (L. glaucoides), and Lesser Black-backed Gull (L. fuscus). At approximately 11:00 Steve located a dark-backed gull with pink legs, and he called us to say that he thought he might have a Slaty-backed Gull, perhaps the same bird we had searched for the day before. We dropped what we were doing and headed directly to the landfill, arriving at 12:20, when we immediately found the bird in question. Steve had been studying and photographing the gull the entire hour we were en route, and he was confident in his identification by then.

The Slaty-backed Gull was in a loafing area just south of the main landfill, on a cleared area in a field with a small, deep pit of open water. Somewhere in the vicinity of 500 gulls were using the loafing area, including hundreds of Ring-billed Gulls (L. delawarensis) and Herring Gulls (L. argentatus), several dozen Great Black-backed Gulls (L. marinus), two or more adult Lesser Black-backed Gulls, one or more immature Iceland Gulls, and one immature Glaucous Gull. We were able to make direct comparisons of the Slaty-backed Gull with Great Black-backed Gulls and Lesser Black-backed Gulls.

We watched the bird continuously until all of the gulls were flushed at 13:33 by a Red-tailed Hawk (Buteo jamaicensis). At that point we lost the bird in the mass of flying gulls. Most of the birds that had been loafing near the landfill left the area and did not return within the next half hour. During the time we watched the gull we took numerous digital photographs through our spotting scope and took video of it with a Sony DCR-TRV830 digital-8 video camera. The gull spent most of the time loafing and preening, and only flew twice during that period. We did manage to capture some images of the spread wings that confirmed the requisite white and light gray mirrors on the primaries (the “string of pearls” Goetz et al. 1986). See Fig.1.

Fig. 1 Slaty-backed Gull Note “string of pearls” 23 Feb 2002 © Kevin and Jay McGowan

A group of birders may have spotted the gull on the frozen north end of Cayuga Lake later in the afternoon, but opinions of the viewers differ. Subsequent attempts to relocate the gull the following day were unsuccessful.

The description of the bird is as follows:

It was a large gull in adult winter plumage. See Fig.2 . It was as big or slightly larger than the male Herring Gulls and substantially smaller than Great Black-backed Gulls. It had a dark mantle that was about the same shade as the Lesser Black-backed Gulls present and lighter than Great Black-backed Gulls.

The head profile was flat. The head and neck were streaked with dirty brownish-gray that was somewhat less extensive than shown by the two Lesser Black-backed Gulls present. The dark smudging around the light-irised eye was conspicuous and was arranged in a flat triangle. The streaked head and mantle color made it confusable with Lesser Black-backed Gulls, not Great Black-backed Gulls. The color of the orbital ring was not noted.

The bill was sturdy, but not too large, yellow with a large red spot on the lower mandible. It had a moderate angle at the gonys. It did not have a huge bill like a Great Black-backed or a Western Gull (L. occidentalis), but it was larger than that of a Lesser Black-backed. The bill was thick and long, did not appear greatly different from a Herring Gull bill, but in the photos it was obviously thicker and longer.

The legs were a bright deep pink and were quite striking. They were nearly purple-pink and distinctively different from any other gull there. The legs of Great Black-backed were the color of dead flesh, while these were vibrant bubble gum. They were very apparently red to KJM, despite his deficiency in red cones. Leg color of gulls is not a character he notices without thinking about it, but these were like no color he had ever seen. The overall appearance was dark, not light like those of the other gulls.

The wings on the perched bird had large white tips to the outer primaries, with the 5th or 6th primary mostly white with a transverse black line. The white on the secondaries and tertials was very broad, broader than the Great Black-backeds near it, and much broader than the Lessers. It showed a very large tertial crescent.

Fig. 2 Slaty-backed Gull 23 Feb 2002 © S. Kelling (Click image to enlarge)

The bird was the least active of all the gulls present. They were all preening and stretching, but this bird refused to do anything for long periods of times. Eventually it flew, and we managed to get some video images. The “string of pearls” (Goetz et al. 1986), pale gray/white subterminal spots (or “tongue tips” Goetz et al. 1986), were apparent from both above and below. From the video captures it appears that p10 had a completely white tip, p9 had a very large white subterminal spot proximal to the subterminal black line that blends into the white tip of p10. P8 showed a dingy white or light gray mark on the inner vane. The obvious subterminal spot was nearly white on p7 and p6, and p5 looked like it had only a thin black line dividing a white tip. Goetz et al. (1986) considered the presence of a tongue on p8 to be diagnostic of Slaty-backed Gull and tongues on p6 and p7 as suggestive of the species. Other species, however, can show similar white spots on p6 and p7, although only rarely on p8 (Gustafson and Peterjohn 1994).

None of the observers had experience with Slaty-backed Gull before this sighting.We compared our bird with descriptions in all available field guides, but no field guide can give a sense of the variability within one species. Fortunately the Japanese Gull Site has a superb series of photos of this species taken in Japan in winter. Our comments are based largely on comparisons with these photos.

The bill showed a rather large gonys bulge, not impossible for Slaty-backed, but perhaps not typical. The Japanese photos show that Slaty-backs typically have a very wide (shallow) angle at the gonys, but that a great deal of variability exists. The steeper angle of the Seneca Falls bird matched that shown on many photos (e.g., the 3rd winter bird at http://isweb15.infoseek.co.jp/animal/larus/slayty_ad.htm; the first two adult shots at http://users.hoops.ne.jp/vegae/SbG01_03_13/SbG010313.html). The first photo at http://isweb15.infoseek.co.jp/animal/larus/Slat11_6ad/slaty116ad.html shows a drastic difference in angle of the two photos on that page, with one matching the Seneca Falls bird.

Usually winter Slaty-backeds have the basal two-thirds of their bill pink-flesh colored and the distal third yellowish. The bill changes to all-yellow by breeding. The Seneca Falls bird seemed to have a greenish and yellowish bill base. All the November and December Japanese photos have the two-toned bill. But the February and March photos show the bills all-yellow, so the change must occur around that time. One photograph was taken on 23 Feb, and its bill matches the Seneca Falls bird.

Slaty-backeds tend to have a round-headed look. Our bird was rather flat-headed. We can match the profile with some of the Japanese photos, but it does look flatter than most.

Other species of dark-backed gull can be ruled out. Great Black-backed Gulls have a much darker mantle, are significantly larger, have paler legs, a thicker bill with a steeper angle at the gonys, and a different wingtip pattern. Lesser Black-backed Gulls are similar in overall appearance to this bird, but have yellow legs. The sturdier bill shape, heavier neck and body, and extensive white in the wingtip also works against Lesser Black-backed. Western Gull is ruled out by the streaked head (virtually unstreaked in Western) and wingtip pattern (more black in outer primaries and no subterminal spots), as well as by the lighter eye and darker legs. Kelp Gull (L. dominicanus) has a darker mantle, less white in the wingtips, yellow legs, and virtually no streaking on the head in winter. A hybrid of Herring and Great Black-backed gulls is a possibility. Although rare, these hybrids do occur (Foxall 1979). Such a bird would be about the same size and similar mantle color of the Seneca Falls bird, but all known specimens show the leg color to be whitish or very pale flesh color, the head streaking to be less extensive than that shown by typical Herring Gulls, the mantle to be lighter than Slaty-backed, and the wingtip pattern to be different (Foxall 1979).

Was this the same bird as was seen in Sullivan County two days before? It certainly shares the overall appearance of the plumage and head streaking, although several characters might differ between the two (P. A. Buckley, pers.comm.). Seneca Falls is 134 miles (216 km) northwest of the Neversink Reservoir, where the first gull was seen. Gulls are known to move large distances in central New York in the winter. Gulls using the Nanticoke Landfill in Broome County were shown to roost on Cayuga Lake, 40 miles (64 km) distant (Curtis et al. 1995). One Herring Gull marked in Broome County appeared at the Seneca Meadows Landfill within a week of being marked (Curtis et al. 1995), showing that the populations of gulls at those landfills mixed. If gulls move 40 miles from a roost to a feeding location and back, then they could easily move 80 miles in one day. We believe it would have been possible for the Slaty-backed Gull to leave Sullivan County on Friday 23 Feb , perhaps joining gulls at the Whitney Point Reservoir in Broome County, almost exactly mid-way between Neversink Reservoir and Seneca Falls on a straight line. It then could have made the trip of the same distance the next day to Seneca Falls.

Regardless of whether this was the same gull as seen in Sullivan County, it, together with the Long-billed Murrelet (Brachyramphus perdix) seen the previous December (Kelling and Kelling 2002), and the large flights of nearly all species of winter finches added to the Siberian atmosphere of the winter in the Cayuga Lake Basin.

Images of this bird may be viewed at:     http://birds.cornell.edu/dic/slbgul/index.htm.

Thanks go to Steve Kelling for finding the bird, and to Robert H. Lewis for his stimulating criticisms of our identification. We learned a lot by researching the answers to them, and those answers strengthened our conviction in our identification.

Literature Cited

Curtis, P. D., C. R. Smith, and W. Evans. 1995. Techniques for reducing bird use at Nanticoke Landfill, near E. A. Link Airport, Broome County, New York. Proc. East. Wildl. Damage Control Conf. 6: 67-78.

Foxall, R. A. 1979. Presumed hybrids of the Herring Gull and the Great Black-backed Gull – a new problem of identification. American Birds 33: 838.

Freer, V., J. Haas and P.A.Buckley. 2002. Slaty-backed Gull in Sullivan County, February 2002. The Kingbird 52:114-118

Goetz, R. E., W. M. Rudden, and P. B. Snetsinger. 1986. Slaty-backed Gull winters on the Mississippi River. American Birds 40: 207-249.

Gustafson, M., and B. Peterjohn. Adult Slaty-backed Gulls: variability in mantle color and comments on identification. Birding 26: 243-24

Kelling, S., and T. Kelling. 2002. Long-billed Murrelet (Brachyramphus perdix) at Ithaca, New York 17-20 Dec 2001. Kingbird 52: 38-40.