Species limits in the woodpecker genus Centurus (Aves). Bulletin of the AMNH ; v. 124, article 6

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New York : [American Museum of Natural History]
"This study is concerned with the systematic relationships among certain populations of woodpeckers of the genus Centurus occurring in the United States, México, and Central America. Significant conclusions arising from this investigation, which has involved field work in México in 1958 and examination of large numbers of museum specimens, are as follows: The generic name Tripsurus is regarded as a synonym of Centurus, since there is no known character or combination of characters that distinguishes species currently assigned to these two nominal genera. Moreover, one species, chrysogenys, that is invariably assigned to Centurus is actually more closely related to species currently assigned to Tripsurus. Centurus (sensu lato) is closely allied with, and possibly inseparable from, Melanerpes. Quantitative analysis of morphologic characters of specimens that represent populations of the aurifrons complex fully supports the view of Ridgway (1881) and Griscom (1932) that these populations belong to a single, highly polytypic species, since even the most strongly differentiated forms (C. a. aurifrons and C. a. dubius) intergrade in zones of contact. It is advocated that the number of subspecies for continental populations be limited to five; these are C. a. aurifrons (including C. a. incanescens of recent classifications), C. a. dubius (including C. a. leei of Cozumel Island, Yucatán), C. a. grateloupensis (including C. a. veraecrucis), C. a. santacruzi (including C. a. pauper and C. a. fumosus), and C. a. polygrammus (including C. a. frontalis). The color and pattern of the plumage in Centurus species are presumably cryptic, and geographic variation in these characters shows a reasonably close correlation with regional variation in climate and vegetation type. The brightly colored, sexually dimorphic areas of the head (and perhaps also the brightly colored belly region) presumably have epigamic significance. It is probable that Centurus hoffmanni of Costa Rica and Nicaragua is specifically distinct from C. aurifrons. Field work in restricted zones of sympatry between Centurus aurifrons and C. uropygialis in Aguascalientes and Jalisco indicates that the two forms are specifically distinct. Approximately 5 per cent of the specimens taken in the zones of sympatry show evidence of hybrid origin, but gene exchange between the two forms is not extensive, if in fact it occurs at all. The presence of traces of yellow pigment on the nape of specimens of C. uropygialis throughout its range is interpreted not as evidence of present-day introgression of genes from C. aurifrons but as a vestige of a character more fully developed in a population ancestral to C. uropygialis and currently being lost in that species. A specific relationship of Centurus aurifrons and C. carolinus is demonstrated by their sympatry without interbreeding in a narrow zone in Texas. Contrary to the suggestion of Peters (1948), Centurus hypopolius is probably not conspecific with C. uropygialis, and it may be more closely allied to C. chrysogenys, with which it is sympatric in Puebla and Morelos. The Haitian woodpecker, Chryserpes striatus, which has been assigned to Centurus by Bond and others, is not closely allied to any species of Centurus or Melanerpes and should be placed in the monotypic genus Chryserpes, as advocated by W.D. Miller, pending further study of its relationships. The significance of ecologic range or amplitude in distribution and speciation in birds is discussed. For Centurus it is suggested that the evolution of reproductive isolating mechanisms tends to proceed more rapidly than does the evolution of ecologic isolation, with the result that competition and other interspecific interactions prevent extensive sympatry of closely related species of the genus. The possible ecologic significance of increased degrees of sexual dimorphism in size, particularly in bill length, in certain insular woodpeckers is discussed, but, in the absence of comparative ecologic and behavioral studies, no satisfactory explanation of the phenomenon can be given"--P. 267.
p. 217-273, [4] p. of plates : ill., maps ; 27 cm.
Includes bibliographical references (p. 268-273).