130 U.S. NATIONAL MUSEUM BULLETIN 233 



eggs. During the four years of his study, 1,981 redwing eggs were 

 laid in the 653 nests with these 15 cowbu"d eggs. These data show 

 an expected distribution of 2.1 percent of nest parasitism and an 

 incidence of parasitism of 0.8 percent per redwing egg. Of the cow- 

 bird eggs, 14, or 93.3 percent, failed to hatch. Six of them were 

 doomed by the situation in which they were laid: 3 in abandoned 

 nests, 2 deposited at least six days after the incubation of the hosts' 

 eggs had begun, and 1 laid on cattail stalks just below a nest. The 

 hmited distribution of parasitized nests and the very low survival 

 success of the cowbud eggs indicate that the redwinged blackbird is 

 not a favorable host species. 



In Decatur County, Kansas, L. R. Wolfe (in litt.) found that the 

 redwings very frequently were parasitized. He wrote me that "prob- 

 ably 90 percent of the redwing nests contained one or more eggs of 

 the cowbird, and I remember frequent extended searches to find a 

 nest without eggs of the parasite. During the years 1909 to 1914 I 

 probably collected twenty or more sets of the thick-billed redwing 

 with cowbird eggs." The incidence of cowbird parasitism in Decatur 

 County as summarized by Wolfe is much higher than has been reported 

 in any other area. From Nebraska have come more than 30 records, 

 a fact which suggests a high incidence there as well. In Colorado, 

 Lincoln (1920, p. 69) considered the redwing one of the species most 

 frequently parasitized, but he gave no quantitative data. It appears 

 that at Brenham, Texas, the Gulf Coast race of the redwing, littoralis, 

 frequently is victimized by the dwarf race of the cowbird. Nye (1936, 

 p. 87) refers to the eggs of this redwing as consisting of the "usual 

 sets of three plus a dwarf cowbird egg or two." 



About 180 records have been noted, distributed among provinces of 

 Canada — Alberta, British Columbia, Manitoba, Ontario, Quebec, 

 Saskatchewan — ^and the following of the United States: Arizona, 

 Arkansas, California, Colorado, Connecticut, Illinois, Indiana, Iowa, 

 Kansas, Maryland, Michigan, Minnesota, Missouri, Montana, Ne- 

 braska, New Jersey, North Dakota, Ohio, Oklahoma, Pennsylvania, 

 Rhode Island, Texas, Utah, Washington, Wisconsin, and Wyoming. 

 All three races of the cowbird are involved, and nine races of the red- 

 wing: phoeniceus, littoralis, megapotamus, arctolegus, fortis, nevadensis, 

 calif ornicus , neutralis, and sonoriensis. The racial combinations so far 

 recorded are as follows: M.a. ater has been found to parasitize phoeni- 

 ceus, littoralis, megapotamus, arctolegus, and Jortis; M.a. artemisiae is 

 parasitic on arctolegus, fortis, nevadensis, and calif ornicus ; M.a. obscurus 

 victimizes megapotamus, californicus, neutralis, littoralis and son- 

 oriensis. If the proposed race utahensis should be accepted offi,cially, 

 to it would have to be referred a record of cowbird parasitism published 

 by Bee and Hutchings (1942, p. 82). 



