1914] Grinnell: Mammals and Birds of the Colorado Valley 189 



Vireosylva gilva swainsoni (Baird) 



Western Warbling Vireo 



First noted April 1, opposite Cibola. Thenceforth of almost daily 

 observation at all our stations from there to Pilot Knob, where still 

 common May 14. At times numerous in the willows; a few noted in 

 the mesquite belt. Evidently a plentiful migrant through the region. 

 Fourteen specimens taken, nos. 13537-13550. 



Lanivireo solitarius cassini (Xantus) 

 Cassin Vireo 



Occurred only in April and as a transient. First seen on the 7th 

 of that month on the Arizona side ten miles below Cibola. One was 

 found on the 9th singing volubly from an ironwood in a desert wash; all 

 the rest seen were in the willow belt. On the California side, twenty 

 miles above Picacho, several were noted April 10 and 11. Thereafter 

 none were seen anywhere. Four specimens, nos. 13533-13536. 



There is also in the Museum a skin (no. 4247) taken by J. 6. 

 Cooper at Fort Mohave, May 14, 1861. 



Vireo belli arizonae Ridgway 



Arizona Least Vireo 



First detected early in the morning of March 8, on the California 

 shore opposite The Needles. Heard repeatedly the same day from 

 both banks as we floated down to lower Chemehuevis Valley. Nests, 

 a year or more old, were seen both in the vicinity of The Needles and 

 above, and the inference was that the species arrived throughout the 

 region in full force on the above date. Thenceforth the species was 

 met with at all stations all the way down the river, being one of the 

 most characteristic avifaunal elements in the riparian strip. The bird 

 foraged in all of the component associations, but was perhaps best 

 represented in the willow association, especially where there was an 

 undergrowth of guatemote (Baccharis glutinosa). 



On the Arizona side above Bill Williams River. March 14, I was 

 able to make some observations on local distribution. Here the willow 

 association was narrow but well defined, and the vireos were closely 

 confined to it. A singing male occupied each segment of about 200 

 yards in this belt, just about the same spacing as the Lucy warbler 



