Sept., 1915 A WALKING EAGLE FROM RANCHO LA BREA 181 species to the genus Morphnu?s instead of to Geranoaitus is based upon differ- ences in the head of the tarsometatarsus. The length of the tendinous bridge is less in Morphnus, as is likewise the development of the outer hypotarsal ridge. The difference is constant though slight. The affinities of the fossil specimen as indicated by these characters are with Morphnus. Distinctive characters of the species are: extreme elongation of the tarsal shaft; weakness of the distal trochleae, which are set less obliquely on the shaft and are less grooved; extreme reduction of the ratio of power arm to resistance arm. In Aquila this last-named ratio is .303, in Morphnus guianensis it is .171, in the fossil species but .125. Table of measurements in millimeters of Morphnus ?aggettt, tarsometatarsus: Total length over all ...................................................................................................... 167.0 Transverse diameter of head ..................................................................................... 20.8 Transverse diameter through trochleae .................................................................. 22.8 Transverse diameter of shaft ...................................................................................... 9.1 Length of power arm ...................................................................................................... 20.6 Ratio of power to weight arm ..................................................................................... 125 The species is named in honor of Mr. F. S. Daggett, through whose kindness the collections at the Museum of History, Science, and Art have been opened to the writer's inspection. Los Angeles, California, August 1, 1915. ESTIMATED AVERAGE AGE OF THE HERRING GULL* By JOHN TREADWELL NICHOLS INTRODUCTION T THE A. O. U. CONGRESS held in Washington in 1914, the writer pre- sented a paper on the proportions of different ages of the Herring Gull, as bearing on the average age which birds of the species reach. The pro- portion of first year birds was estimated from data gathered by observing gulls from ferry-boats in New York Harbor, supplemented to some extent by observa- tions on Long Island and elsewhere. During the season of 1914-15 more data has been similarly collected, and the results obtained, if not unimpeachable, are believed to be interesting and worthy of publication. They indicate an average age of 16.2 years attained by birds which have reached the second winter, and very high mortality between the first and second winters. ARGUMENT In Science for October 25, 1912, page 565, is a suggestive article by W. J. Spilhnan, of Washington, D.C., entitled "A ]?ethod of Determining the Average Length of Life of Farm Equipment", in which it is shown that in dealing with a constant population of either inanimate or animate objects, "if we divide the total number of objects of all ages . . . by the average number in their first year the quotient will be the average length of life that those now in their first year will live". By this formula the numbers of first-winter Herring Galls divided into the total Herring Gull population gives their average length of' life. First- year Herring Gulls are dark in plumagel readily separable from second year or
- Read at the A. O. U. Congress, San Francisco, May 18, 1915.
