Unidentified dark-mantled gull at sea off New York, 11 Feb. 2006

Introduction: During a fantastic winter pelagic excursion off Long Island, New York (run by Paul Guris & See Life Paulagics), we paused over a wreck site on the Hudson Valley Shelf. Attracted by our chumming, a good number of large gulls and Atlantic Gannets settled in rafts around the boat. Frank Gallo quickly noticed an extremely interesting dark-mantled gull sitting in amongst the American Herring and Great Black-backed Gulls. Slightly smaller than the Great Black-backs, the mystery bird (Figs. 1-7) appeared to be an adult, with a noticeably paler mantle than the adult black-backs, with an immaculate unstreaked white head and brighter colored bill. Indeed, almost everyone aboard was able to pick out the bird by this combination of features.

At first we thought we had an adult Lesser Black-backed Gull, however, it became quickly apparent that multiple features were inconsistent with this identification. The legs were the first point of concern, being pinkish with only a slight orange tint on the upper portion of the tarsus. Although some subadult Lesser Black-backs develop pinkish rather than yellowish legs, this seemed very strange for a bird that otherwise appeared to be a full adult coming into breeding condition. The primaries showed a large mirror on p10 that extended across both webs separated by a dark feather sharft. [Before being corrected by co-observer Andy Guthrie, I initially mistook this bilobed mirror for two mirrors.] Lesser Black-backed Gull typically shows an oval mirror on p10 and a smaller mirror on p9. The broad white trailing edge was striking both in flight and on the water. It is worth noting that the plumage details and bill coloration were very symmetrical and all of the photographs are shown in their original orientation with respect to left and right sides of the bird.

For a detailed discussion of the identification issues click here.

Figure 1. Viewed from below, the white underwing coverts contrasted with the dark flight feathers. A large mirror on p10 is clearly visible on both upper and undersides. Photo Copyright © Angus Wilson 2006.


Figure 2. Orbital ring appeared orange or orange-yellow. At least three primary tips extended parallel to or beyond the tail tip. Notice also the very broad tertial cresent. The bill was heavy and deep, especially at the gonys point giving a slightly bulging look. The bill color was a rich orange-yellow with a small black spot just distal to the orange-red gonys mark and the tip of the bill was pale almost whitish. Photo Copyright © Angus Wilson 2006.


Figure 3. Another view showing the detail of the spread primary tips and details of the head. Notice the very broad white trailing edge to the secondaries and primaries. The black of p10-p8 reaches the primary coverts. Photo Copyright © Angus Wilson 2006.


Figure 4. Closeup of the head. The iris appeared pale yellow seeming darker at a distance. Scrutiny of numerous photographs failed to reveal any dark feathering on the head and neck. Photo Copyright © Angus Wilson 2006.


Figure 5.The webs of the feet were salmon pink and the tail feathers snowy white. Photo Copyright © Angus Wilson 2006.


Figure 6. A better view of the pink legs, with only a hint of orange high up on the tarsus. Photo Copyright © Angus Wilson 2006.

Figure 7. Comparison with Great Black-backed Gull. Photo Copyright © Angus Wilson 2006.

Figure 8. For comparison, here's an adult Great Black-backed Gull photographed at the same time and with the same camera settings. The primary tip pattern is typical for the species and the reddish eye ring is quite obvious. Photo Copyright © Angus Wilson 2006.

See Life Paulagics specializes in pelagic trips off the mid-Atlantic states, principally New Jersey, Delaware, Maryland and New York. By actively chumming throughout the trip, we usually manage to keep a large flock of hungry gulls behind the boat and this often attracts both white-winged gulls, Lesser Black-backed Gull and Black-legged Kittiwakes.


Figure 11. Comparison of the dark-mantled gull with an adult American Herring Gull and 1st-winter Great Black-backed Gull. Note the dark eyed appearance when viewed from a distance. Photo Copyright © Angus Wilson 2006.

Acknowledgements: Frank Gallo first found the bird and immediately got everyone onto it. Many folks aboard the Capt. Lou VII offered valuable comments on the apprearance of the bird and kept constant track of its whereabouts thus aiding the photographers. Special thanks to Paul Guris who master-minded our pelagic adventure and coleaders, Frank Gallo, Shai Mitra, Rich Guthrie and Andy Guthrie for making the trip go so smoothly and for extensive discussions.