372 BULLETIN 17 6, UNITED STATES NATIONAL MUSEUM 



one who is familiar with that sound may easily be deceived. From 

 this point he continues along the arc until he arrives at a point di- 

 rectly above his mate, where he hovers for a few seconds with body 

 horizontal and bill directed downward, rendering his squeaky "song." 

 Then, without change of attitude, he begins to rise rapidly and 

 vertically, repeating the entire maneuver luitil he tires or the other 

 bird departs, with himself in hot pursuit. 



Presumably this practice originated strictly as a courtship display, 

 but it now has a much broader application, frequently being directed 

 at other species or at birds of wholly different kinds. Young males 

 begin performing the flight as early as September of their first year, 

 and it is continued through at least the greater part of the year. 

 Anna's hummingbird is not addicted to the shuttling flight so much 

 used by those species in which the wings of the males are modified 

 in such a way as to produce a metallic rattling sound. The actual 

 mating, which is not often witnessed, has been described by Leroy 

 W. Arnold (1930) : "When first observed, the birds were playfully 

 chasing each other about and suddenly swooped down to wdthin 

 about eighteen inches of the ground where the leading bird, wdiich 

 proved to be the female, stopped and faced about. The male ap- 

 proached and the mating was consummated in the air, the birds 

 breast to breast and with the male somewhat under the female. The 

 male then settled down to the ground for a few moments, fanning 

 out his tail and pointing his beak upward, while the female flew to a 

 nearby perch. After a short rest, the male rose and flew after the 

 female who returned to her former position and mating again took 

 place as before." 



Nesting. — ^With reference to the nesting habits of hummingbirds, 

 few distinctions can be drawn between the various species even under 

 quite different ecological conditions, except in the matters of season, 

 locale, type of site, and nest materials. The nesting of Rieffer's 

 hummingbird {AmapJlia tzacatl tzacatl) in Central America has been 

 carefully observed by Alexander F. Skutch (1931), and the agree- 

 ment in procedure between this species of the humid Tropics and those 

 of the semiarid Temperate Zone is most striking. The principal 

 specific variations in this connection among North American hum- 

 mingbirds concern the selection of materials for the nest, but there 

 is also considerable individual latitude that tends to bridge the gaps. 



Although Anna's hummingbird is generally distributed west of the 

 Sierra Nevada and the Colorado Desert, it is rather definitely classi- 

 fied as a breeder in the Upper Sonoran Zone and is less partial to arid 

 localities than is Costa's hummingbird. The nesting season begins 

 before the arrival of any of the migrants, sets of eggs having been 

 found by various persons as early as December. The nesting prob- 



