: Gj 
280 University of California Publications in Zoology. |Veu. 
Mexico. . . . I feel convinced of the correctness of the 
hypothesis that it was during this long period of separation that 
the two main forms, the western and the eastern, finally got 
established.’’ The hairy woodpeckers, of both east and west, 
are represented by northern and southern forms, which it is 
argued are more recent in differentiation. 
Unhke the woodpeckers in question, the cowbirds are doubt- 
less austral in their origin. But this would not militate against 
the hypothesis of a similar course of divergence. 
In conclusion: It seems improbable that the cowbirds of the 
Great Basin of the northwestern United States have recently 
invaded that area from across the Rocky Mountain region. On 
the contrary, the facts as above presented show that cowbirds 
were to be found in the west as soon as careful observations were 
made; and that the birds of the Great Basin belong to a distinct 
form from that occupying the United States east of the Missis- 
sippi. And finally it appears most probable that this Great Basin 
race is a direct offshoot of a stock-form now represented from the 
southern United States border southward, and not a descendant 
from the Atlantie form. 
TABLE I. 
Molothrus ater artemisiae. 
Ratio % 
of depth 
Depth of of bill 
No.} Locality Date Wing Tail? Tarsus Culmen Gonys pill at base*® to culmen 
8822 Humboldt Co., Nev. May 27, 1909 110.3 72.7 28.3 ness 10.8 10.5 59 
8823 Humboldt Co., Nev. May 28, 1909 112.7 76.0 27.1 18.2 10.9 10.0 55 
Humboldt Co., Nev. May 31, 1909 112.9 72.6 27.9 18.2 ala let / 10.1 55 
Humboldt Co., Nev. May 31, 1909 112.6 73.3 QT 17.5 10.8 9.7 55 
Humboldt Co., Nev. June 1, 1909 ibilaleal 72.7 26.5 18.1 11.0 9.9 55 
Humboldt Co., Nev. June 3, 1909 112.4 12.3 27.71 18.0 10.6 10.8 60 
Humboldt Co., Nev. June 3, 1909 112.2 74.0 28.7 18.8 11.4 10.1 54 
Humboldt Co., Nev. June 5, 1909 115.5 76.2 28.9 19.6 iS 10.7 55 
Humboldt Co., Nev. June 11, 1909 117.2 79.0 28.2 18.3 10.7 10.4 57 
Humboldt Co., Nev. June 11, 1909 117.0 79.5 27.9 18.9 11.5 10.3 54 
8833 Humboldt Co., Ney. June 11, 1909 115.0 75.8 26.4 17.6 10.9 10.7 61 
Average of the eleven adult males 113.5 74.9 27.7 18.3 11.1 10.3 56 
‘Univ. Calif. Mus. Vert. Zool. 
_ 7 The tail is measured from the point between the insertions of the median rectrices into the uropy- 
glum, to the tip of the longest rectrix in “‘closed”’ tail. All measurements are in millimeters. 
The depth of bill is not a satisfactory measurement to secure because of the conical shape of the beak 
and because the mandible and maxilla may have dried either separated slightly or crowded closer together 
than normally; the errors in these regards would, however, seem to neutralize one another. 
