4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I4O, 



Black-capped vireo 



Vireo atricapilla Woodhouse 



Graber's study (1961) greatly extends our knowledge of this vireo. 

 She reported on 76 nests in which a total of 243 vireo eggs were 

 deposited. Of these, 134, or 55.1 percent, were lost before hatching, 

 and of these 134 Graber considered cowbird parasitism accounted for 

 97, or 72.3 percent. In addition, eight vireo chicks were lost because 

 of the presence of cowbird chicks in the nests. The percentage of 

 parasitism of the 76 nests is not given, but it must have been con- 

 siderable as Graber wrote that, ". . . during the nestling period, as 

 during laying, the chief loss was due to cowbird parasitism. In all 

 cases in which a cowbird chick occupied the nest, no vireo chicks 

 survived. . . ." 



Bell's vireo 



Vireo bellii Audubon 



Additional data on this frequent victim of the cowbird is included 

 only to emphasize the statistically unsatisfactory nature of present 

 methods of evaluating the quantitative aspects of host-parasite rela- 

 tions. In my 1963 summary (pp. 84-85) I noted some 82 instances 

 of cowbird parasitism on Bell's vireo, but added ". . . these consti- 

 tute only a fraction of the number that lie back of the numerous esti- 

 mates put forward by various authors . . ." (i.e., authors who ex- 

 plicitly mentioned a number of instances but added loose statements 

 to the effect that the vireo was victimized far more frequently in their 

 area). Since then I have learned of nearly half as many cases more, 

 no less than 28 from two papers alone (Ely, 1957, unpublished thesis; 

 Overmire, 1962). The increase is not a measure of any change in the 

 relationship between the vireo and the cowbird but merely an indica- 

 tion of additional observation and more increments to the recorded 

 data. 



Dwarf vireo 



Vireo nanus Nelson 



Three more cases of parasitism of this vireo at Irapuato, Guana- 

 juato, Mexico, have been found in the Moore collection by Dr. J. W. 

 Hardy. These, and the one noted in my 1963 book (p. 83), were 

 found within one week, June 17 to 26, 1943, indicating a high fre- 

 quency of parasitism locally. 



