UNIVERSITY OF CALIFORNIA PUBLICATIONS 
IN © 
ZOOLOGY 
Vol. 5, No. 5, pp. 275-281, 1 text-figure December 31, 1909 
A NEW COWBIRD OF THE GENUS 
MOLOTHRUS 
WITH A NOTE ON THE PROBABLE GENETIC 
RELATIONSHIPS OF THE NORTH 
AMERICAN FORMS 
BY 
JOSEPH GRINNELL 
(Contribution from the Museum of Vertebrate Zoology of the University of California) 
The recurring suggestion that cowbirds are of recent arrival 
in the west, having newly invaded the domain from the east as 
a consequence of its settlement by man, is not borne out by a 
study of the case. It is possible, even probable, that this bird, as 
with many others, is increasing in abundance with the cultivation 
of the arid regions, and that it is in consequence to be observed 
at many points where formerly not met with. But that the cow- 
bird affords an example of a species which is rapidly extending 
its range across the wide area westward from the Rockies is 
negatived by the available data. 
In the first place, the earliest naturalists to collect birds in 
quantity ascertained the presence of this species even as far west 
as Nevada (Ridgway, Orn. 40th Parallel, 1877, 501: upper Hum- 
_ boldt Valley and Truckee Reservation) and California (Baird, 
Pac. R. R. Rep. 1X, 1858, 525: Sacramento Valley and Fort 
Yuma). 
