(369) THE GLAUCOUS GULL IN WINTER BY G. T. KAY. (Plates 40-53). SINCE the winter of 1941-42 the Glaucous Gull (Larus hyperboreus) has become a comparatively numerous winter-visitor to the Shet­ land Islands. At a refuse dump on the outskirts of Lerwick where it had been rare to see more than half a dozen of these birds together, it is now a common occurrence to see thirty or forty and occasion­ ally as many as a hundred. During the winter of 1945-46, the writer, with others interested in the project, arranged for an attempt to be made to photograph particularly Glaucous Gulls and possibly Iceland Gulls (Larus glaucoides) in the vicinity of the dump. The proposal was to use still and cine cameras from hides. It was hoped that a series of photographs might be secured which would do something towards clearing up the difficulties of dis­ tinguishing between these two species in the field, which have proved to be in some respects greater than used to be supposed. We were fortunate as regards the Glaucous Gull. A series of photographs and 300ft. of cine film were taken of this arctic visitor at most stages of plumage from the bird in its first winter plumage to that of the fully adult. Further photographs were added during the winter of 1946-47. Unfortunately the only Iceland Gull seen during these two winters was a dead specimen ; an immature bird in its first winter which had been captured on a fishing boat off the east side of Shetland on January 16th, 1947. The following remarks are taken from notes kept by the writer during many hours spent at close quarters with Glaucous Gulls of all ages. Considerable attention was given to the feature of the degree of projection of the wing tips beyond the tail. It was noticeable that the wing tips of first winter birds reached well beyond the tail, whereas those of older birds did so in varying degree and, in some adults, not at all. An explanation of this may be culled from The Handbook wherein is stated that, as regards moult, the first winter bird retains, through­ out the winter, the full wing of its juvenile days, whereas the adult has a complete moult from July to November or December and occasionally its outer primaries are not fully grown even as late as February. J. Dwight, in "The Gulls of the World" (Bull. Amer. Mus. Nat. Hist., Vol. ui) informs us that intermediate birds moult as does the adult. Of eight photographs of intermediate and adult birds, showing wing development, taken between January 1st and 18th, none shows a complete wing. In the writer's opinion, none of these wings would have been fully grown until well on through February. During the two winters under review the Glaucous Gulls left us early in February. 370 BRITISH BIRDS. [VOL. XL. The difference between the wing structures of first winter and adult birds is clearly shown on Plate 40. The adult bird came into the writer's hands on December 18th, 1946, and the immature bird on December 29th, both in fresh condition. The wing of the im­ mature bird is fully grown, while the growth of the outer primaries in the adult wing is such that the second primary had something over four inches still to grow on December 18th. Exactly one month later a photograph was taken of an adult with wings which had only then reached the same stage of development. Of particu­ lar interest regarding the above birds is the fact that both had fully- grown tails. The attenuated tips to the primaries of the first winter wing are well shown, a feature which is not repeated in subsequent moults, when rounded tips like those of the adult are grown. This feature has value in distinguishing between first and second winter birds at close quarters. If the birds (some 30 -to 40) towards which we directed our attention during the winter of 1946-47, when wing photography was concentrated upon, were average specimens, then the following generalizations may be made. The question whether the wing tips reach beyond the tail, in the winter months, is dependent on whether a bird is in its first winter or not. If in its first winter plumage, which is the darkest of the stages seen in Britain, the bird will have a fully grown wing reaching well beyond the tail. If it be an older bird, the projection may be nothing or very little up to the end of January, according to the development of the moult, and a fully grown wing is unlikely to be seen until February. It may be added that the only birds seen with wings which did not project at all were fully adult. The soft parts of the Glaucous Gull are described in The Handbook as similar in colour to those of the Herring-Gull {Lams a. argentatus), with the exception of the orbital ring. The writer has found the following differences. The bill of the first winter bird is creamy flesh colour, with dark brown tip, the dark area being roughly one quarter the area of the bill. The dark tip decreases with age, but is still evident in birds which have assumed the grey mantle. The bill of the before-mentioned first-winter Iceland Gull was also creamy flesh colour with dark brown outer portion, but this portion was approximately half the area of the bill. The bill of the first winter Herring-Gull is of course all dark except for a small portion at the base of the lower mandible, which is pale. The feet and legs of the adult Glaucous Gull, in the winter, are pinkish flesh colour, distinctly brighter than those of the Herring- Gull. Although the pinkish tint is not so bright in the immature birds, it is pronounced at all ages. Howard Saunders gives feet and legs of adult as "bright flesh pink"; a very good description. It is of interest here to note that Messrs. Nicholson and Longstaff, quoted in The Handbook, give pale flesh colour, with a leaden tint, as the colour of feet and legs of the adult Iceland Gull, in summer. Those VOL. XL.] THE GLAUCOUS GULL IN WINTER. 371 of the adult Glaucous, in the winter, could never be so described. When adult Glaucous and Herring-Gulls are seen close together, the difference in the colour of the irides may be noted ; pale lemon in the Herring-Gull, but bufnsh-lemon in the Glaucous. The iris of the first winter bird is dark brown and becomes paler, with a greenish tint, in the second winter. Even when examined at very close quarters with binoculars, the adult bird appears to have no colour in the orbital ring in winter. The adult handled on December 18th, 1946, had only the faintest trace of lemon-yellow in the orbital ring. At other times silent, the adult Glaucous at the bait gives voice as readily as any of the other gulls. Its commonest call is the equivalent of the " kyow-kyow-kyow " of the Herring-Gull, but is much shriller and has nothing like the same carrying power. It resembles very much the first squeaky attempts of the immature Herring-Gull to make the call. The wailing note is very similar to that of the Herring-Gull, perhaps a shade more mellow. The tamest of the three gulls, the Glaucous is generally the first to return to a bait after being disturbed and, being in possession, normally keeps off the Great Black-backed Gull (Larus marinus). The situation, however, is reversed when the Great Black-backed Gull is in possession. In the presence of any of these gulls, the Herring-Gull keeps discreetly in the background. A difference in the size of individual birds is a feature which seems to be more noticeable with the Glaucous Gull than with other gulls. In addition to the wing measurements of a large Glaucous over­ lapping those of the Great Black-backed Gull and of a small Glaucous those of the Herring-Gull, the difference in the body bulk of individ­ uals, as seen in the field, is very marked. Probably it is because of this difference in size that the slow wing-beat of the Great Black- backed Gull is noticeable in some birds and not in others. The Handbook informs us that the moults of Glaucous and Iceland Gulls are apparently similar and this is confirmed by J. Dwight (I.e.). All that has already been said about the wing development of the Glaucous Gull will consequently apply equally to the Iceland Gull. Dwight also states that the one is simply a miniature of the other in every way. In the writer's opinion there are fairly distinct differences, apart from size. In any case size alone does not settle the matter as the small female Glaucous and the large male Iceland Gull come very near to each other in this respect. This brings us to the really small Glaucous Gull, one of which is well shown on Plates 47 and 48, a bird which is little if any larger than a Herring- Gull. This bird was photographed in mid-April, 1939, and no doubt shows the full length of the adult wing. It will be seen that the wing tips project beyond the tail quite considerably. Why, it may be asked, is this bird a Glaucous and not a large Iceland Gull ? It was not seen by the writer but was identified by Mr.