Sept, 1915 A WALKING EAGLE FROM RANCHO LA BREA 181 
species to the genus Morphnus instead of to Geranoaetus 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 daggetti, 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 
A T THE A. 0. 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. 
Spillman, of Washington, D. C., entitled “A Method 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 Gulls divided 
into the total Herring Gull population gives their average length of life. First- 
year Herring Gulls are dark in plumage, readily separable from second year or 
*Read at the A. O. U. Congress, San Francisco, May 18, 1915. 
