This study of the parasitic weaverbirds is an entity in itself, complete as far as available data permit. It is also a part of a general survey of the problem of avian brood parasitism, in the course of which, besides many pertinent short papers, monographs dealing with other families of parasitic birds were issued by me on the cowbirds (1929), on the African cuckoos (1946), and on the honey-guides (1955). To complete the series I hope eventually to publish a comprhrnsive comparative an interpretive summation of the biological aspects of the subject.
For many years I hesitated to write the present portion of the survey because the available information was fragmentary, and there was little reason to expect that the accounts resulting from this information would lend themselves to clarifying comment. Although new information has been exceedingly slow in coming into print and our present knowledge is still obviously fragmentary, now, after 35 years of patiently watching for such items in the literature, and of extensive correspondence with resident observers in the homelands of the birds involved, in addition to personal fieldwork in Africa, I venture to present the picture, incomplete to be sure, but sufficiently filled in to reveal in general outline the nature of brood parasitism in] the weaverbirds.
In the first part of this study is presented the evolution of brood parasitism, and in the second the data on which I have based my interpretation. The study should, I hope, stimulate observers to supply further data and at the same time expedite their work by directing them to the gaps that I have not been able to close.
During the course of my studies, many persons and organizations have assisted me in many ways, all of which contributed to the degree of completeness attained in the following pages. Not that I consider the problems fully worked out or the solutions arrived at as definitive, but I would not have been able to come as far as I have without these contributions. My personal field work in southern and eastern Africa was supported first, in 1924-25, by the National Research council through funds supplied by the Rockefeller Foundation, and later, in 1950-51, by grants from the John Simon Guggenheim Memorial Foundation, the American Philosophical Society, and the Smithsonian Institution. Without the generous support of these sponsoring groups the field work would not have been possible, and the study would not have been undertaken.