VIII IJ.S. NATIONAL MUSEUM BULLETIN 233 



been little change in our knowledge of the screaming cowbird, only a 

 short summary is given for this species. 



Inasmuch as the completeness of our knowledge varies with the 

 different species of cowbirds, the detailed discussion of such biolog- 

 ical matters as host selection, the relative frequency with which 

 different species of these hosts are utilized, the success rate with 

 which these birds serve as fosterers, and the various reactions they 

 give to the parasite and to the incidence of parasitism are all given 

 in the account of each species of cowbird. As might be expected 

 from the interest discussed above, the data are incomparably more 

 extensive, and thus more amenable to analysis and interpretation, 

 for the North American brown-headed cowbird than for any of the 

 others. Because of this, the chief biological discussion and sjmthesis 

 are given under that species, even though parts of the thoughts and 

 conclusions are applicable to the others as well. 



The present study of the host-parasite relations of the cowbirds 

 has been a long time in progress. Not only has a great mass of data 

 been accumulating slowly over several decades, but newer insights 

 and better methods of evaluating and interpreting the facts have 

 been brought to bear as the material permitted. Much of the present 

 data is due in large measure to the kind cooperation of many observ- 

 ers, collectors, and custodians of collections, all of whom have 

 generously sent me numerous interesting records that otherwise 

 would not have been available. 



As previously mentioned, my first discussion of the subject appeared 

 in 1929, and short supplements, chiefly of new host species, have 

 been issued at intervals between 1931 and 1949. Since acknowledg- 

 ments were made in each publication to the individuals who con- 

 tributed information, it is imnecessary to repeat them in the present 

 work. However, those contributors subsequent to my 1949 paper 

 are given here in alphabetical order. While it is true that many 

 deserve a greater measure of thanks, all sent me what they could, and 

 it is better to express my gratitude impartially. 



I am indebted to the following for their contribution to the prepara- 

 tion of this work: Mrs. F. C. K. Anderson, Georgetown, Barbados; 

 Dr. A. J. Berger, Ann Arbor, Michigan; Mr. D. A. Boag, Edmonton, 

 Alberta; Mr. T. D. Burleigh, Washington, D.C.; Mr. E. A. CardiflP, 

 Bloomington, California; Mr. E. J. Court, Washington, D.C.; Dr. I. 

 McT. Cowan, Vancouver, British Columbia; Mr. R. S. Crossin, 

 Tucson, Arizona; Mr. A. R. Davidson, Victoria, British Columbia; 

 Mr. W. E. Godfrey, Ottawa, Ontario; Dr. P. Harrington, Toronto, 

 Ontario; Mr. E. N. Harrison, Los Angeles, California; Mr. F. Haver- 

 schmidt, Paramaribo, Dutch Guiana; Gunnar Hoy, Salta, Argentina; 

 Mr. J. B. Hurley, Yakima, Washington; Mr. J. D. Hyatt, Anniston, 



