RUFOUS- WINGED SPARROW 907 



nearly excludes other plants. There on May 20, 1952, I saw little 

 else than a few flowering Erigeron divergens and the crucifer Descurainia 

 pinnata. 



Factors that induce nesting. — It does not seem, however, that 

 mere abundance of plants or insects or a given amount of rain will 

 per se cause the rufous-winged sparrow to nest. Nesting depends on 

 the readiness of the female, because in most if not all years the male 

 seems to be in breeding condition long before actual nesting occurs, 

 (A reverse situation, with the male in full breeding condition away 

 from the usual breeding grounds long ajter nesting, occurs in the 

 same region in A. cassini — ^A. R. PhiUips, 1944.) Nesting by the 

 female is apparently triggered by additional factors which, at present, 

 we can only guess. Thus in 1959-60, rainfall was again above normal 

 in December and January; this was followed, April 10 to 20 and later, 

 by a plague of army cut-worm moths, Chorizagrotis auxiliaris (fide 

 William X. Foerster). The weather, of course, always becomes very 

 warm by May and June at Tucson. Neither Robert Crandall nor 

 I was there in 1960, but several friends kindly looked in vain for 

 evidence of unusually early nesting of A. carpalis. Some factor, 

 apparently, was missing. 



Certainly a most important aspect of the rufous-winged sparrow's 

 nesting is the lack of concordance between different areas, and prob- 

 ably even between close neighbors within the same httle colonies, in 

 the breeding activities of the females. A proper understanding of the 

 factors that trigger nesting will thus require the amassing of more de- 

 tailed data over long periods of time. Based on data as of 1963, the 

 only reasonable conclusion is that nesting depends on certain unclear 

 ecological conditions within the pair's territory. Obviously no 

 fashionable all-inclusive theory can possibly explain the strange facts 

 about to be presented; these do not coincide with dates, photoperiods, 

 amounts of cloud cover, darkness or sunshine, cyclonic or anticyclonic 

 vreather, temperature variations, or other current phenomena. 



The rufous-winged sparrow responds, instead, to the most potent 

 of several perhaps conflicting environmental factors, like the responses 

 of certain nesting passerine birds in Latvia (Vilks, 1958), and its 

 individual variability parallels that of some Austrahan ducks (Frith, 

 1957). Both it and other Aimophilae {rvficeps herein; see H. Wagner, 

 1955), as well as all the birds of the arid parts of AustraHa (Keast, 

 1960), afford overwhelming evidence against the automatic photo- 

 period hypothesis expounded by A. Wolfson (1960), A. H. Miller 

 (1960) and D. S. Farner and A. Oksche (1964). (For an excellent 

 review of this subject see A. J. Marshall, 1951.) 



A particularly interesting problem, which would requu-e far more 

 time to investigate than I could devote to it, is whether nests built 

 when conditions first begin to look favorable are abandoned if the 



