184 University of California Publications in Zoology [Vol.12 



Many cliffs, from the vicinity of The Needles on down the river, were 

 seen with remains of nests adhering to their faces in rows or patches. 

 The first birds noted were a very few flying high overhead near 

 Riverside Mountain, March 17. Next seen near Ehrenberg, March 26. 

 Several were seen April 12 coursing over the river and bottom lands 

 twenty miles north of Picacho. Not noted again until May 5, when 

 at Yuma a large colony was seen constructing nests on the steep rocks 

 on the Arizona side near the prison. The birds were gathering mud 

 at the edge of the river on the California side, thronging back and 

 forth over the unusually narrow channel at this point. 



On the California side in the vicinity of Pilot Knob two large 

 nesting colonies were in evidence. One was on a sandstone bluff of 

 some twenty-five feet height past which the main current of the 

 river swung with exceptional speed. Here the nests were attached, 

 to the number of ninety-seven, mostly as yet incomplete, to the irregu- 

 larly eroded surface of the rock from ten to twenty feet above the 

 surface of the river at its present stage — evidently above the reach 

 of the highest level at flood time. Four of the finished nests were 

 investigated on May 9 and found to contain in two cases three fresh 

 eggs, in two cases one fresh egg. 



On the same day, sixteen of the birds were shot for specimens. 

 The skiff was repeatedly rowed out from shore a little below the 

 colony, and as it was swept down stream by the current was pulled 

 back again by means of a long rope manipulated by a man on shore. 

 Those swallows flying nearest the boat upstream in front of the colony 

 were shot at, so that the dead birds would float past within reach. 

 Of the sixteen secured, fifteen were males. There is no way that 

 I know of to determine sex until the birds are in hand. This would 

 seem to indicate that the females at this time in the breeding season 

 are most retiring, and that the males are the ones to make demonstra- 

 tions of alarm when the colony is invaded by an enemy. 



The other colony located had taken possession of the concrete walls 

 in the head-gates of the Imperial Canal at Andrade. The nests were 

 being constructed in crowded rows in the lateral upper corners beneath 

 the woodwork bridging the piers. The birds were gathering mud at 

 the margin of the canal nearby, alight with uplifted wings. Four 

 shot were all males. 



The superintendent of the canal, stationed at Andrade. complained 

 that the swallows proved a nuisance by dirtying up the painted wood- 



