1506 U.S. NATIONAL MUSEUM BULLETIN 23 7 part 3 



broods averaged only 2.4 song sparrows, indicating that each cowbird was reared 

 at the expense of one song sparrow. In one instance Nice *** found that a pair 

 of song sparrows raised a young cowbird together with five of their own young. 

 Apparently here no loss of sparrows was involved. In another paper, Nice (1936) 

 noted that, in all the song sparrow nests which she had watched during a period 

 of five years, adult cowbirds removed 5.7 percent of the song sparrow eggs and 

 nestling cowbirds crushed or starved 3.5 percent of the young sparrows. The 

 cowbird eggs did not succeed as well as those of the host; only 30.7 percent of 

 the former, but 35.8 percent of the latter, reached the fledgling stage. In 1930-31, 

 there was one female cowbird to about 11.5 pairs of suitable hosts, but in 1934-35 

 there was one to 8.6 pairs of suitable victims. 



Of all song sparrow nests parasitized, Nice reported that 70 percent held a 

 single cowbird egg each, 27 percent held 2 each, and 3 percent held 3 each. In 

 the area of study — near Columbus, Ohio — the song sparrow was the most impor- 

 tant host of the paeasite [sic]. Norris (1947***) noted that 11 out of 27 nests 

 (40.7 percent) in Pennsylvania were parasitized, and Berger (1951***) recorded 

 37 out of 59 nests found in Michigan (62.7 percent). In the Detroit area, as 

 reported by the Detroit Audubon Society (1956***), the average frequency of 

 parasitism of the song sparrow was 40.1 percent of all the nests found * * *. 



One is drawn toward attempting an over-all estimate of the frequency with 

 which the song sparrow is victimized, but to do so with any feeling of accuracy 

 is difficult because the incidence of parasitism appears to vary geographically 

 (or, at least, the frequency with which it is reported varies). From this it follows 

 that the over-all percentage depends on how many geographically different areal 

 data are used in the estimation. [With one group of studies from the eastern 

 United States] ***, we come up with a total of 323 parasitized nests out of 804 

 nests observed, or a little over 40 percent. On the other hand, in southern Quebec 

 (Terrill, 1961, p. 11), out of 486 nests observed, only 62, or 12.7 percent, were para- 

 sitized. If we put all these studies together, we get a total of 382 out of 1,285 

 nests victimized, or 29 percent. This figure becomes yet smaller when we attempt 

 to include data from other parts of the continent. 



[One color-banded song sparrow in a single summer] *** had no fewer than five 

 consecutive nests * * *. It would seem that, if none of these nests had been 

 interfered with, there would not have been sufficient time for four or five in one 

 season. * * * It appears that one of the effects of parasitism may be to increase 

 the "nesting potential" of the host. * * * 



As many as 7 cowbird eggs have been found in a single nest of this sparrow; 

 there are numerous records of 3, 4, and 5 parasitic eggs to a nest. Occasionally, 

 but not often, song sparrows may partly bury cowbird eggs by building a new 

 nest lining over them — if the alien egg is laid before any eggs of the host. 



Salmon (1933, p. 100) has reported seeing a song sparrow feeding three fledgling 

 cowbirds; no young sparrows were mentioned. Lees (1939, p. 121) recorded that 

 near Wetaskiwin, Alberta, he watched a song sparrow feeding no less than five 

 young cowbirds. Tins must be a record of fledgling success for any host species. 



Friedmann (1963) lists no instances of parasitization by the bronze 

 cowbird of subspecies of the song sparrow covered by these life 

 histories. Only the Mexican race mexicana has been involved. 



Other enemies of the song sparrow are at least four species of 

 hawks (Munro, 1940; Randall, 1940; Hamerstrom and Hamer- 

 strom, 1951; Heintzelman, 1964) and at least five species of owls 

 (Allen, 1924; Hawbecker, 1945; Johnston, 1956; Fisler, 1960; Graber, 



