156 University of California Publications in Zoology [Vol. 12 



The Colorado River ravens, as shown by the accompanying table, 

 are of the usual sinuatus dimensions. The whitening of the basal or 

 down portions of the nuchal feathers in desert representatives of the 

 corax group would seem to be a modification in the direction of the 

 condition as it finds its extreme in cfyptoleucus, and probably because 

 of coming under the same conditions. But no use of the feature is 

 apparent. 



MEASUREMENTS IN MILLIMETERS OF COBVVS CORAX SINUATUS 

 FROM THE COLORADO VALLEY 



Locality Date •£ f» fr g § D 5 § O OS 



Riverside Mt.. Calif. Mar. 16 440 242 70.0 60.0 74.0 52.5 36.3 25.8 



10 m. S. Ehrenberg, Calif. Mar. 30 414 222 66.8 59.5 69.2 50.1 34.3 25.1 



10 m. S. Cibola, Ariz. Apr. 7 381 224 64.8 61.7 67.4 48.0 33.0 26.2 



Fort Mohave, Ariz. Jan. 6 410 212 64.7 58.2 65.6 45.3 31.9 24.2 



Fort Mohave, Ariz. Jan. 6 423 221 65.8 59.0 68.9 49.0 32.9 25.3 



Collected by J. G. Cooper in 1861. 



Molothrus ater obscurus (Gmelin) 

 Dwarf Cowbird 



Cowbirds were first seen when we reached Ehrenberg. March 25. 

 Here, on the Arizona side, flocks aggregating approximately one hun- 

 dred individuals were staying close about the town. They were either 

 roosting quietly in mesquites among the adobe ruins, or flying about in 

 compact, unanimously acting flocks, or feeding in company with other 

 blackbirds in cattle pens. In one case a bunch of fully forty were 

 feeding close together on the ground in a calf corral, all with uptilted 

 tails and quivering bodies, a mannerism peculiar to the species. They 

 were eating millet seeds, and the crops of those taken were crammed 

 with this material. One flock was seen flying north along the California 

 side opposite Ehrenberg. On the same side, opposite Cibola, during 

 the first week of April a number were seen, now in pairs haunting the 

 bottom lands close to the river. 



The species was next seen April 17 on the California side twenty 

 miles north of Picacho at the Draper ranch, four individuals; then 

 eight miles east of Picacho, April 20, a small flock. On the Arizona 

 side again, five miles north of Laguna, April 24 to 27, several pairs 



