by Donna L. Dittman & Steven W. Cardiff

BRIEF HISTORY

Territorial "black-backed" gulls were first noted on Curlew Island in the Chandeleur Island chain on July 8, 1989 by Lawrence P. O'Meallie (photographs) and R. D. Purrington. The pair of displaying adults was initially identified as one of the blacker-backed subspecies of Lesser Black-backed Gull (Larus f. fuscus or L. f. intermedius). In 1990, as this record began its first circulation through the Louisiana Bird Records Committee, Paul McKenzie was the first to comment that the Curlew Island gulls were almost certainly not Lesser Black-backed Gulls and that the birds' appearance was more suggestive of Kelp Gull (L. dominicanus), a widespread southern hemisphere species. Much discussion ensued over the identification and origin of the Curlew Island "Kelp" gulls. The "black-backed" Chandeleur gulls were again reported the summer of 1990, with the same pair present on Curlew (L. O'Meallie) and a single individual present on Grand Gosier (Richard Martin).

Although the identification of the Chandeleur birds appears to be relatively certain based on extensive photos and process of elimination, acceptance of the first North American records has been stalled by the lack of voucher specimens and the issue of natural vagrancy versus human-assisted origin. To date, Kelp Gull has not been accepted by the LBRC, ABA (review of accepted Texas record(s) Galveston 1995, 1996 is in progress) or AOU. I n 1987 "Black-backed" Gulls were observed on Mexico's Yucatan Peninsula (Jorge Correa S.). Publication of Louisiana "Kelps" in American Birds Central Southern Regional Summaries (Purrington 1990; Am. Birds 44: 1143-1147) provided the incentive to follow-up on the Yucatan gull identification, and a photographic documentation was obtained in May 1991. Subsequently, Howell et al (1993) published "First records of the Kelp Gull in Mexico" (The Euphonia 2(4(: 71-80). Colonization of the Chandeleurs by Kelp Gulls may be related to the appearance of Kelp Gull on the Yucatan. Possible Kelp Gulls have been reported in other coastal Louisiana sites (Fourchon and Rutherford beaches, Baptiste Colette), Texas, and Indiana. There are no other reports of Kelp Gull in the New World north of Ecuador or Brazil.

Coinciding with the appearance of the apparent Kelp Gulls on the Chandeleurs was the colonization of those islands by breeding Herring Gulls, previously unknown as breeding birds in Louisiana and a very rare breeder elsewhere on the Gulf Coast. In fact, the first observation of a breeding Herring Gull in Louisiana was of a bird paired with an apparent Kelp on Grand Gosier in 1990; perhaps more importantly, the Grand Gosier pair produced at least one viable offspring (R. Martin - photographs).

By 1994, in addition to a pair of pure Kelp Gulls, there were several pairs of Herring Gulls breeding on Curlew Island, as well as various pairs of birds presumed to be intermediate- looking hybrids, hybrids paired with pure Herrings, and hybrids paired with pure Kelps. In 1997 and 1998, a similar situation existed on Curlew Island, except that the numbers of Herring Gulls have gradually increased, and no pure pairs of Kelp Gulls were detected.

Whatever the origin of the Kelp Gulls in the Gulf of Mexico, their occurrence and subsequent hybridization with Herring Gulls, and the continuing breeding of both parent species and hybrids has a tremendous and under-appreciated implication on identification of large, dark-mantled gulls on the Gulf Coast

QUICK REVIEW OF GULL PLUMAGE TERMINOLOGY

Good basic information regarding gull topography is contained in Gulls, a Guide to Identification, by P. J. Grant. For this article it is important for the reader to understand the following information. Definitive alternate plumage is the bird's adult breeding plumage; large gulls usually acquire this plumage as four year olds. This plumage is obtained through a partial (body feathers only, no flight feathers are replaced) pre-alternate molt that begins in the late winter and progresses through the spring. This plumage is characterized (in the species covered here) by an immaculate white head, and adult soft part colors (orbital ring, iris, bill, and leg color). The "mantle" technically refers to the bird's upper back, but for convenience, it is commonly expanded to include all of the back and upperwing coverts. The f light feathers include primaries and secondaries. The ten primaries (attached to the bird's "hand") are numbered backwards from the outermost feather (=#10; contra Grant) and the secondaries are attached to the bird's arm bone (ulna) between the primaries and the body. The outer primary is all black with a white tip or subterminal spot or "mirror" and, depending on the species, the other nine primaries are black distally, some with "mirrors" and with various amounts or shades of gray (or all gray). All primaries are tipped white when fresh, but these tips may "wear" off by late spring or summer. "Mirrors" are white subterminal spots surrounded by black (or gray), and are not to be confused with the white primary tips. The bases of the primaries and secondaries are covered above and below by sets of feathers arranged in rows (coverts). In definitive alternate plumage, the upperwing coverts are the same color as the back; the underwing coverts (referred to as the underwing "linings") are white. A "secondary bar" is formed when there is contrast between the upperwing coverts or underwing lining, and the secondaries, or their tips. In definitive alternate plumage, a secondary bar is prominent only on the underwing, when the bird is viewed in flight from below.

PART 1: ADULTS IN DEFINITIVE ALTERNATE PLUMAGE

Because of potential hybrids, identification of pure Kelp Gull must be approached with extreme caution. Careful examination of mantle color, primary pattern (especially that of the underwing), orbital ring and leg color, and overall structure, are required to differentiate Kelps from superficially similar species or potential hybrids. No other adult white-tailed gull species, except Great Black-backed, possesses a nearly black mantle with little or no contrast between black primaries and blackish-gray mantle. Definitive adult Great Black-backeds have a distinctive primary pattern (a large, all white tip to primary #10 with a prominent white mirror on primary #9) and ivory-pink legs. Great Black-backeds are also substantially larger in all aspects, sex for sex (although small female Great Black-backeds probably overlap with large male Kelps). Kelp Gulls are approximately the size of a Herring Gull, and are therefore larger on average than most Lesser Black-backed Gulls (considering only L. f. graellsii, the largest subspecies and the only subspecies recorded in Louisiana). Kelp Gulls have heavy angled-looking bills and long, heavy greenish-yellow legs with proportionally "big" feet. No "pure" Kelp has been observed thus far in Louisiana with non-yellow legs. (The apparent Kelps on the Yucatan Peninsula are similar.) Kelp Gull shares its primary pattern (one window on primary #10) with three other relatively dark-mantled gull species: Lesser Black-backed, Yellow-footed (L. livens), and Western (L. occidentalis wymani). These species also share the same underwing pattern of uniformly black outer four primaries blending to dark gray and then forming a dark stripe along the broadly white-tipped secondaries (see illustration); the dark undersurface of the primaries and secondary bar is not well- illustrated in current field or gull guides. This feature is more pronounced on Kelp by virtue of the much blacker upper surface of the wing, further exaggerating the dark secondaries seen from below. Kelp Gull shares the same orbital ring color as Lesser Black-backed, most Western (L. o. wymani; may also show darker iridies) and Yellow-footed gulls. Documentation of "pure" Kelp Gulls should include photographs that focus on the above characters.

Hybrids pose a much more difficult problem.. Presumed first generation ("F1") Kelp X Herring Gull hybrids are superficially like Lesser Black-backed or Yellow-footed Gulls. Structurally more like a Herring or Kelp gull, the "F1" hybrid does not appear as proportionately long-winged as a Lesser Black-backed (in flight or when perched). The mantle color is most like graellsii Lesser Black-backed or Yellow-footed gulls, the pattern of the upper surface of the primaries (one window on primary #10) is the same, and the "F1" hybrids have yellow or greenish-yellow legs. The best way to differentiate the hybrids is to concentrate on the pattern of the undersurface of the wing while the bird is in flight. With good views, gray "tongues" bleed up into the black primaries, most noticeable on primaries number 4-7 and give the impression of a black wedge (somewhat reminiscent of a kittiwake, but not as extreme). A shadow of dark gray runs back along the secondaries (see illustration) but does not blend from black to gray as in the Kelp or Lesser Black- backed gulls. An "F1" can be picked out at a distance by the dark undersurface of the secondaries (unlike the essentially pale silvery gray secondaries of a Herring). A dark-mantled hybrid can be confused with a pure Kelp, especially under backlit or otherwise poor viewing conditions and without close inspection of the underwing pattern and mantle color. The orbital ring color of thee hybrids has been noted as orange (intermediate between the two parental types). "F1" hybrids can be separated from Lesser Black-backeds by the combination of size and structure (retaining more Herring or Kelp-like features), underwing patten, and orbital ring color.

Presumed "backcross" hybrids are even more problematical. "F1" hybrids have been observed paired with Kelp, "F1" and Herring gulls. Assuming that the mantle color will be intermediate between the parents, "F2" offspring can therefore have a range of potential mantle colors. A Kelp X "F1" will likely have a mantle darker than a Lesser Black-backed, but lighter than the typical Kelp. An "F1" X Herring offspring should be lighter backed than a Lesser Black-backed, yet still noticeably darker than a Herring.. During our recent visit, all birds we assumed to be "F2" hybrids (mantles paler than a Lesser Black- backed) had legs appearing grayish-green or gray. This could lead to possible confusion with California Gull (L. californicus), primarily in sub-adult plumages. Adult California Gulls is easily separated from adult greenish-gray or gray-legged hybrids by the combination of dark brown iris, black spot next to red gonys spot, and distinctive primary pattern (all white tip on primary #10, window on primary #9). A "F1" X "F1" hybrid could conceivably retain "F1" features, or even express characters of the grandparents. Of course, this possibility exists for any hybrid pairing

We have only scratched the surface by discussing adult gulls in alternate plumage. The puzzle is much more complicated! To date we have not observed first-summer Kelps or first summer hybrids on the islands. A few presumed second and third year hybrids (dark mantles, gray or yellow legs) are present; most sub-adults we assume remain on the "wintering" grounds. The whereabouts of the "missing" sub-adults and where the post-breeding adults go (if anywhere) is currently a mystery.

So get your camera ready. A whole new era for gull identification begins. Please submit all photos of possible Kelp Gulls to the LBRC. The LBRC does not review records of hybrids, but to help us track the progress of these gulls, please submit photographs of potential hybrids to the authors. Thanks in advance. Museum of Natural Science, 119 Foster Hall, Louisiana Stare University, Baton Rouge, LA 70803