October, 1922 - 445 
MIGRATION RELATIVE TO BIRD SIZE 
A CONSIDERATION OF THE DATA CONCERNING BIRD MIGRATION SHOWS THAT 
SMALL BIRDS, HAVING GREATER ENDURANCE, MAKE THE LONGEST JOURNEYS 
By CHARLES K AVERILL 
1 HAVE clipped from the daily papers 
of the season of 1921, accounts of 
some of the college eight-oared races, 
containing the weights and statures 
of the members of the crews. The aver- 
age height of the members of thirteen 
crews is 6 ft. 0^ in., but the average of 
the stroke oar is 5 ft. 11 in., or 1>4 in. 
shorter. From “The Complete Oars- 
man,” by R. C. Lehman, I figure that 
from 1888 to 1908 in the Oxford-Cam- 
bridge races the average weight of the 
stroke was 8.7 lbs. less than that of the 
crews. It is stated, in “Rowing and 
Track Athletics,”, by Crowther and Rull, 
that “the stroke oars have usually been 
small men.” Mechanically better, with 
more power and reach are the larger 
men, but the stroke oar who must be 
depended on to maintain his physical 
condition to the end of the race has the 
smaller stature. 
In Dr. Sargent’s book on Athletics 
(Outdoor Library, Scribner and Sons) 
the stature of the ideal runner for dis- 
tances of one mile and over is about 5 ft. 
8 in., but the sprinter from 100 to 440 
yds. is about 2 in. taller. That en- 
durance in Marathon runs favors the 
smaller man is noted by Ernest Hjert- 
berg in his “Athletics in Theory and 
Practice.” 
The original British horse was a pony 
about 14 hands high. The horses of the 
Turks and Barbs, built for endurance 
and speed, were not more than 14)4 
hands. Desiring more speed in a short 
run the English raised this to 15 and 
16)4 hands. In all these cases the me- 
chanical advantage of size is opposed by 
the advantage of endurance which is al- 
'ways with the smaller; the result is a 
tendency to a standard size for each 
purpose. 
I N birds there is probably no mechanical 
advantage in the larger size, in fact 
it is a matter of simple arithmetic that 
of two birds proportioned alike as to 
linear measurements, the smaller has the 
greater wing surface in proportion to its 
bulk. The smaller bird then of those 
similarly formed succeeds better in pro- 
longed flight, being favored both by en- 
durance and mechanical advantage. Ob- 
viously this does not apply to soaring 
■flight which only large birds can accom- 
plish. If we compare any two North 
American birds of the same genus or 
tw’o races of the same species, whose 
migrations differ greatly in extent, we 
Courtesy American Museum of Natural History 
The western sandpiper migrates from 
Alaska to Peru 
shall find the smaller bird making the 
longer migration. 
Of the three North American Curlews 
the Eskimo, least in size, makes the long- 
est migration, traveling from Arctic 
shores to far south of the Equator, while 
the Long-billed Curlew does not range 
Courtesy American Museum of Natural History 
The long-billed curlew has a short 
migration 
much beyond the limits of the United 
States, and the Hudsonian Curlew, in- 
termediate in size, makes a migration 
apparently intermediate in length. The 
migratory Great Blue Heron is smaller 
than its near relative Ward’s Heron, 
which is resident in the Gulf region. Of 
the two Godwits the smaller Hudsonian 
ranges from Arctic regions to Patagonia 
in its migration, while the Marbled God- 
wit only ranges from the Valley of the 
Saskatchewan to Guatemala. The mi- 
grations of the Sora, Yellow and Black 
Rails far exceed those of the larger Vir- 
ginia, King and Clapper Rails. 
. It will be of interest to compare some 
resident forms of the Alaskan Islands 
with those of the western mainland. 
This can be done by means of “Ridg- 
way’s Birds of North and Middle Amer- 
ica,” where the length, wing, tail, bill and 
tarsus of each bird is given. Whethei 
these birds are closely related species, 
subspecies, or only individuals is of no 
importance for our purpose; they are 
birds that do not migrate compared with 
those that do. The Aleutian Leucos- 
ticte, Aleutian Snow Bunting, Aleutian 
specimens of the Alaskan Longspur, and 
the Kadiak Winter Wren will be found 
to have greater length and longer wing, 
bill and tarsus than the mainland birds. 
It will not be necessary to give these 
figures as the statements can easily be 
verified by anyone who has a copy of 
Ridgway’s work. The great size of the 
Aleutian Song Sparrow' is probably to 
be ascribed to its more northerly range 
as compared with the other races of that 
bird, but this cannot be said of such cir- 
cumpolar species as the Longspur and 
Snow Bunting. 
'THE Ovenbird whose summer range 
extends north to southern Macken- 
zie and Newfoundland, and whose north- 
ern limit in winter is somewhere south 
of central Florida and the Gulf States, 
has resident individuals in the Bahamas. 
Ridgway show's comparative measure- 
ments of these with specimens from dif- 
ferent parts of the mainland, and each 
measurement of the Bahaman specimens 
is larger. The samp is true of the Abaco 
Pine Warbler, resident in the island of 
that name, compared with the Pine War- 
bler. The Nassau Pine Warbler, an- 
other Bahaman race, is not especially 
different from the- Pine Warbler in size. 
The American Crossbill, Pine Gros- 
{Continiied on page 478) 
