"Thayer's" Gull in the Niagara Frontier Region

Abstract

DURING autumn and winter thousands of gulls are often present on the Niagara River. Most are Herring (Larus argentatus), Ring-billed (L. delawarensis), and Bonaparte's Gulls (L. philadelphia), and they can be observed particularly well at such favored concentration points as Niagara Falls and the lower river in the Lewiston-Queenston vicinity. As the Niagara is usually ice-free in winter, varying numbers of gulls are able to subsist even during the coldest periods. During past years local birders have noted on the river adult-plumaged gulls with characteristics similar to those described for Thayer's Gull, a form presently treated as a subspecies (L. argentatus thayeri) of the Herring Gull (A.O.U., 1957) and recently considered a species (L. thayeri) by Smith (1966) based on his studies in northern Canada. During December 1954 and January 1955 first one and later three of these birds were observed about Niagara Falls and described by Coggeshall (1955) in a paper discussing the taxon and reviewing its history. Prior to 1967 two or three attempts to secure an adult specimen failed, partly because of the difficulty in approaching and retrieving the birds in the Falls area. A specimen in first-winter plumage H. D. Mitchell collected on a Buffalo Harbor dump 4 February 1945 ( 8 ?, BSNS no. 2857) was subsequently sent to L. Griscom, who identified it possibly as L. glaucoides kumlieni (Beardslee and Mitchell, 1965: 244). On 24 December 1957 at the dump on Squaw Island, Buffalo, along the edge of the Niagara River, I secured a gull (sex indeterminable, BSNS no. 4107) that is almost identical in size and coloration to the 1945 first-winter bird. A comparison of these two immature gulls with material in the Royal Ontario Museum and the National Museum of Canada has shown that they agree well with specimens of Thayer's Gull from northern Canada and the Pacific coast. The culmens of the two immatures from Buffalo measure 42 and 41 mm respectively. Two first-year female specimens of L. a. thayeri in the Royal Ontario Museum, taken in September in Bellot Strait, Northwest Territories, Canada, have culmens measuring 37.1 and 41.3 mm. Although three of these culmens measure less than the smallest such measurement (42 mm) that I can find published for female Thayer's Gull, as W. E. Godfrey (pers. comm.) pointed out, first-year gulls often have smaller bills than adults. Also some shrinkage may have occurred in these specimens. In addition, the great majority of published culmen measurements for female Thayer's Gulls are those by Smith