Reviews

9•A X 6•/• in., paper.$1.25.--Afterpublishing his classic study The cowbirds in 1929, Friedmann continued to accumulate information about this group of icterids.He reported some of it in supplemental notes that appeared from time to time down to 1949.Now he has pulled together all of it and much additional published material to prepare a comprehensive report.Like its forerunners, it is a scholarly work--careful, thorough, we]I-documented, and fully indexed.The 19-page bibliography should prove to be invaluable to every student of brood parasitism.Since Friedmann's list of hosts of the Brown-headed Cowbird alone includes 206 species, mostly small songbirds, there is scarcely a student of birds in North America who will not find something of interest in it.The greater part of the work consists of a discussion of each of the species reported to have received in its nests the eggs of the Brown-headed Cowbird, Molothrus ater, or Bronzed Cowbird, Tangavius aeneus, the North American members of the family.Briefer treatment is accorded the ]ess we]] known Shiny Cowbird, Molothrus bonarlensis, and Screaming Cowbird, Molothrus rufo-axillarls, of South America and the Giant Cowbird, Psornocolax oryzivorus, of Central and South America.It is much more, however, than an annotated list of host species.It contains also a general discussion of several aspects of the parasitic relationship--frequency of host selection, intensity of parasitism of frequent hosts, breeding success of host and parasite, and other topics.As might be expected, nearly three-fourths of the text is devoted to the Brown-headed Cowbird and its hosts in the United States and Canada, where the greatest amount of field work has been done.I know of no recent book more likely to stimulate ideas for research in the minds of amateur field students.It is impossible to read through it without seeing, at almost every turn of the page, questions awaiting investigation, some of which might be illuminated in the course of the study of other common species.One could argue convincingly that the Brown-headed Cowbird is the most inviting bird for study in North America.Although it is common in nearly all the populous parts of the continent and has captured the imaginations of ornithologists for more than a century, some of the most elementary facts of its behavior and ecology are still obscure.The number of eggs laid in a season by a cowbird is still uncertain.The effect of the cowbird on the reproductive success of its host has been examined critically for only a handful of host species.Whether individual Brown-headed Cowbirds specialize, except fortuitously, on certain host species is unknown.Why should the frequency of parasitism of one host vary astonishingly from one locality to another although the cowbird is common in both?In the American Redstart, for example, Friedmann reports an exceedingly wide variation in parasitism, 2 per cent to 70 per cent, in different localities.The inquiring mind will ask if the critical factor here could be the distance of the nest into the depths of a woodland, with the nests near the edge suffering more heavily.An extreme case of variation is the Red-winged Blackbird, which seems rarely to be molested east of the Mississippi River (parasitized nests often numbering ]ess than one per cent of Red-winged Blackbird nests) but becomes one of the principal hosts in the Great Plains (according to one report "probably 90 per cent").Friedmann suggests that the eastern Red-winged Blackbirds often nest colonially in cat-tail marshes where they protect each other's nests by "combined aggressiveness and 234 Reviews [ Auk Vol.81 broadly categorized or, for the most part, not mentioned.I have been given to understand, however, that the senior author is preparing a more comprehensive work dealing with the same area.As to be expected, the report includes a number of new records for the Pet•n.A sight record of a male Progne subis by the junior author does not eliminate the possibility that the bird seen may have been a similarly-plumaged form, such as cryptoleuca, previously recorded from Guatemala, or even the South American modesta, recently reported from Key West.A better acquaintance with the voices of the birds would no doubt have increased the frequency of a number of species and altered the relative status, say, of Megarhynchus pitangua and Pitangus sulphuratus.Contopus cinereus, as another example, could not be differentiated from C. virens during the period of migration, according to the authors, though I think it can be in tone of coloration, proportions, mannerisms, and voice.The statement that 37 forms consist of visitants which are all common Central American winterers should be modified to exclude some 10 species that are uncommon to rare or lacking in southern Central America.These qualifications do not detract from the usefulness of the paper as a check-list.The concluding Discussion analyzes the area faunally and subregionally, largely in numerical fashion, in relation to the drier Yucatan Peninsula and the wetter eastern Guatemalan lowlands.It indicates how the recent re-creation of cutover habitats and newly-made reservoirs have led to the arrival of some species but not as yet of others and, vice versa, how habitat destruction may be accompanied by the quick disappearance of some species and not of others.•P.SLvD.Pavo, The Indian Journal of Ornithology.•Publishedby the Society of Animal Morphologists and Physiologists.1963.3I. S.

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