144 University of California Publications in Zoology [Vol.12 



side Mountain. March 17 to 21. At our station above Blythe, March 

 22 and 23, this hummer was for the first time numerous, both males 

 and females occurring along the desert edge of the riparian bottom, 

 feeding among bushes of Lycium andersoni. At Ehrenberg the last 

 week of March and opposite Cibola the first week in April, the species 

 was abundant in the desert washes, feeding about the profusely blos- 

 soming palo verdes. Noted at all stations below the latter point, 

 though in lesser numbers. 



The males were more seldom seen, and the females became closely 

 restricted to the willow strip along the river, in which association we 

 were convinced that this was the only species of hummingbird breed- 

 ing. The males were not seen in the willows, but only in the mesquite 

 association and up the desert washes. The females foraged everywhere 

 except on the desert mesa, but nested exclusively in the willows. 

 Nest-building was in progress April 12, on the California side twenty 

 miles north of Picacho. Nests, each with two small young, were found 

 April 18 and 20, on the same side eight miles east of Picacho. Many 

 full-grown young-of-the-year were feeding about the lavender flowers 



Fie. G. Vertical sectional diagram of nest (no. 769) of Archilochus alex- 

 andri. Note position as regards supporting stalk, and construction of rim (see 

 text, p. 145). X %. 



