1914] Grinnell: Mammals and Birds of the Colorado Valley 183 



The species was next observed April 30 and May 1 in the bottom 

 lands four miles below Potholes (in California), and then, on the 

 same side of the river, five miles northeast of Yuma, May 3 and 4. At 

 each of these places a dozen or more individuals were seen. On both 

 sides of the river in the vicinity of Pilot Knob, May 5 to 15, this 

 tanager was frequently observed. While the call note was closely 

 similar to that of the western tanager, present as a migrant in numbers 

 at tbc same time, the song was quite different, being a clear, full-toned 

 warble more nearly like that of the black-headed grosbeak, yet with 

 an individuality of its own. 



The Cooper tanager. as far as our observations went, is strictly 

 confined to the willow association. Not one bird was seen even so far 

 from this association as the mescpiite belt. The species is evidently 

 a regular summer visitant. 



The ten specimens secured, nos. 13423-13432, are all males. One 

 of these was thought to lie a female until dissected, as it is in a greenish- 

 yellow phase of coloration. However, there are scattering pale reddish 

 feathers in nearly every feather tract, though there is no indication 

 that any molt is in actual progress. This is probably a case of 

 arrested molt. 



The notable absence of female specimens in our series resulted in 

 spite of our greater effort to secure that sex. It was not that the 

 males were more conspicuous, though this may have been a factor 

 against that sex. but that the females were at this season extremely 

 wary. As a pair was approached the female was always first to take 

 alarm. I was repeatedly able to distinguish females at a distance as 

 soon as males, in some cases sooner, after having located the pair by 

 their notes. The red of the male appeared to be neutralized by tbc 

 shimmering green of the surrounding foliage, so that the male was no 

 more quickly discerned than the female. The male, however, was far 

 more conspicuous in flight across open spaces. 



There are in the Museum two skins (nos. 4202, 4203 ) taken by 

 J. G. Cooper at Fort Mohave. April 2!). 1861. 



Petrochelidon lunifrons lunifrons (Say) 



Cliff Swallow 



This swallow is evidently a common breeding species along the 



Colorado River wherever appropriate nesting sites are afforded. But 



we found the birds remarkably late in arriving and in nest-building. 



