1914] Grinnell: Mammals and Birds of the Colorado Valley 143 



districts of California. It is quite possible that the species is a com- 

 paratively recent invader of the latter regions, hailing originally from 

 the more arid deserts, with which its pale coloration would appear 

 to associate it most closely. 



There are in the Museum two skins (nos. 4185, 4186) taken by 

 J. G. Cooper at Fort Mohave, April 23 and May 23, 1861. 



Chaetura vauxi (Townsend) 



Vaux Swift 



Appeared as a migrant. First seen at Potholes. April 29, two 

 individuals: next, one, on the following day, four miles south of 

 Potholes. Very many were observed May 4 along the California side 

 five miles northeast of Yuma ; these were flying in a general northerly 

 direction across the woods and river, irrespective of the local trend 

 of the latter. May 5 a flock was seen at the mouth of the Gila, near 

 Yuma. May 9 the last was seen, a single individual among cliff 

 swallows near Pilot Knob. Two specimens secured, nos. 12774, 12775. 



Aeronautes melanoleucus (Baird) 



White-throated Swift 



Observed as follows : March 1 and 5, on the Arizona side among 

 The Needles, seen to enter a slanting crack in the face of the cliff; 

 April 4, on a precipitous mountain peak about five miles west of the 

 river opposite Cibola, seen to enter and leave a crevice in the rock 

 wall; April 19, eight miles east of Picacho, flying overhead; May 2, 

 four miles south of Potholes, overhead. Not more than two individuals 

 were noted at any of the above localities. 



Archilochus alexandri (Bourcier and Mulsant) 



Black-chinned Hummingbird 



First noted March 3, one of each sex, on the California side oppo- 

 site The Needles; next March 7, several on the Arizona side at the foot 

 of The Needles. Here they were feeding about the flowering bushes 

 of Lycium andersoni. Noted on the California side in the lower Chem- 

 ehuevis Valley, March 9, one specimen ; several on the Arizona 

 side above Bill Williams River, March 13 and 14; several at River- 



