Iceland Gull

Mew Gull: This gull had the proportions of a Mew Gull but had pale wingtips, which are not shown by Mew Gulls. Also, it was considerably larger than a Mew Gull, as mentioned by its comparison with California Gulls.

Thayer's Gull: Thayer's Gulls are among the most likely species to be confused with Iceland Gulls, and indeed some hybrids are indistinguishable. However, I believe this bird can be determined as a pure Iceland Gull based on the following traits. In flight, the band across the tail feathers was very indistinct, not as bold as in even a light Thayer's Gull. The secondaries and outer primaries in flight did not contrast with the rest of the wing as much as they do in Thayer's Gull. The outer webs of the primaries also did not contrast with the inner webs like they would on a Thayer's Gull. Although differences are subtle and perhaps clinal, this bird seemed smaller and slighter than a Thayer's. The wingtips of this bird were about the same color as the wings; in some light they appeared lighter, and in some very slightly darker. In Thayer's the wingtips are usually darker than the wings, although they can be about the same color for a very pale Thayer's. The pink base of the bill can contribute to the identification in either of two ways: Iceland gulls have lighter bases of the bills than Thayer's Gulls, and first-winter Thayer's Gulls do not show any pale, let alone the extent shown by this bird, until much later in winter. This bird had even more pink than may be typical for Kumlein's-type Iceland Gulls, and appears more typical of nominate Iceland Gulls in this respect. An alternative explanation is that this is a second-winter bird. Second-winter Thayer's and Iceland Gulls both have pale bases to the bill and dark tips. However, second-winter Thayer's Gulls have gray mantles (they have lost the pale brown mottling of a first-year bird), while Iceland Gulls sometimes retain this juvenile mottling into their second winter. This explanation would also require this bird to have retained its dark eye into its second winter, which is not common but is also not rare. Either way, the combination of bill and mantle color helps eliminate Thayer's in support of Iceland Gull as an identification for this bird. Thayer's gulls also have dark-centered tertials, whereas this bird has finely patterned tertials that are typical of Iceland Gulls. Iceland x Thayer's hybrids have been recorded, but are typically intermediate in most or all of the features discussed. This bird seems to me to be solidly in line with Iceland in every trait.

Glaucous Gull: Most Glaucous Gull subspecies can be easily discerned from this bird by their large size, robust bill, and large head with a sloping forehead. However, the subspecies "barrovianus", which is found in Alaska, can overlap with Iceland Gulls in size. Plumage is also nearly identical between Iceland Gulls and Glaucous Gulls, so we must pay close attention to structure. One diagnostic trait is wing length: Glaucous Gulls have wing tips that barely project beyond the tail, whereas Iceland Gulls have long wing tips that project well beyond the tail, as shown by this individual. Even in a small female "barrovianus", the head is relatively large and flat compared to Iceland Gulls and this Gull. "Barrovianus" do not have the huge robust bill typical of Glaucous Gulls, but their bills are still larger and have a stronger gonydeal angle than shown by this bird, which has a bill typical of a smallish Iceland Gull. Although this bird has a pink bill base and a dark tip, this demarcation is not as distinct as the "ink-dipped" tip of a Glaucous Gull, although extreme Kumlein's gulls can approach this ink-dipped look even in their first winter.

Hybrids: Some hybrids that can be confused with Iceland Gull include Glaucous-winged x Herring, Glaucous x Herring, and Glaucous-winged x Glaucous. I beleive these all can be eliminated for the same structural reasons that pure Glaucous and pure Glaucous-winged can be eliminated, as discussed above. Herring hybrids also have dark secondary bars and tail bands, which were both lacking in this individual.

For the purposes of this report, I am considering Kumlien's Gull to be a subspecies of Iceland Gull, i.e., as Larus glaucoides kumlieni. I have not attempted to distinguish between Larus glaucoides glaucoides and Larus glaucoides kumlieni.