Avian systematics and evolution in the Gulf of Guinea : the J.G. Correia collection. Bulletin of the AMNH ; v. 100, article 3

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New York : [American Museum of Natural History]
"Systematic notes on a large collection of birds made on three of the four islands in the Gulf of Guinea, West Africa ... by Mr. and Mrs. J.G. Correia are presented. Complete lists of the land and fresh-water birds of the four islands are given, and it is indicated which forms are endemic on the various islands, and which races (three in number) are described from the islands (in every case Fernando Po) as new in this paper. In addition, Cyanomitra cyanolaema octaviae and Oriolus nigripennis alleni are described as new from the mainland of West Africa. The following additional taxonomic changes are proposed: that the genera Lampribis and Hagadashia be united with Bostrychia; that Creciscus be united with Crex; that the following races, usually synonymized, be recognized: Accipiter castanilius beniensis, Tyto alba poensis, Stizorhina fraseri rubicunda from West Africa to separate it from the nominate race, which proves to be restricted to Fernando Po, Chalcomitra rubescens stangerii from Fernando Po, Malimbus rubricollis rufovelatus from Fernando Po, and Lamprocolius splendidus lessoni from Fernando Po. Two insular kingfishers, thomensis and nais, of the genus Alcedo (Corythornis) are made races of leucogaster, rather than of cristatus. Fernando Po has an avifauna like that of West Africa with which it was once united, but less rich. Isolation has been great enough to produce endemic races in about 30 percent of the resident species, but there is only one endemic species and no endemic genus. Principe and São Tomé are much more isolated and were never connected with the mainland, from which they differ ecologically to a considerable extent. A number of endemic species and a few endemic genera, as well as endemic races, are found on these two islands. Two of the genera, one genus from each island, are distinct enough to offer some difficulties as regards family assignment. Principe and São Tomé share a number of endemic species, yet each has a number of characteristic endemics lacking on the other. Faunal relationships to Fernando Po are very slight, and each of the three islands has, to a large extent, derived its fauna independently from the mainland. No consistent trends in color character are apparent in the avifaunas of these islands. The birds of Fernando Po are often slightly larger and longer billed than those of West Africa. On Principe and São Tomé similar trends are noticeable and have progressed further, so that several of the endemic forms are very large for the groups in which they belong. But there are exceptions, for example, the dwarf ibis of São Tomé (Bostrychia bocagei). None of the environmental rules seems adequate to explain the trend towards larger size in such a large segment of the birds of the Gulf islands, and it is suggested that intraspecific rivalry for mates or for food under insular conditions (empty ecological niches, relative absence of predation) may have selected for increased size. In a few cases only, where double colonizations are involved, does interspecific competition appear to have been important in this respect. In such cases, one of a pair of competing species will, of course, be selected for smaller rather than larger size. Increase in size of the bill, a common phenomenon in these insular birds, is in some cases due to allometric correlation with general size. In other cases it may be due to direct selection for a larger bill, either for feeding or for gaining dominance over other individuals of the same species. 'Compensation' may be involved. The São Tomé giant sunbird, Cyanomitra thomensis, is shown to be an excellent example of several aspects of allometry and also of the increase in sexual dimorphism in size which, as Rensch has recently pointed out, often characterizes the larger species of a related group"--P. 449.
p. 397-451, 4 p. of plates : ill., map ; 27 cm.
Includes bibliographical references (p. 449-451).