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Evolution in the Family Dicruridae (Birds)

Ernst Mayr and Charles Vaurie
Evolution
Vol. 2, No. 3 (Sep., 1948), pp. 238-265
DOI: 10.2307/2405383
Stable URL: http://www.jstor.org/stable/2405383
Page Count: 28
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Evolution in the Family Dicruridae (Birds)
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Abstract

(1) The family Dicruridae (drongos) consists of 20 Old World species, most of them tropical. Their classification is discussed. (2) The evolution of the taxonomic characters of the family is investigated. The characters of the more specialized species, such as large size, frontal crests, long tails, and modifications of the outermost tail-feathers have arisen independently in different branches of the family. Evolution within the family has been restricted to a realization of a limited number of trends. (3) Every species character varies geographically. This is shown for general size, pigmentation, proportions, and special structures (crests, tail-rackets). (4) The geographical variation of many characters is not haphazard, but correlated with such features of the environment as temperature and humidity. Island birds are frequently larger or smaller than the populations on the adjacent mainlands. (5) The number of subspecies per species varies from 1 to 32, averaging 5. Some of these subspecies are very young since they have formed on new islands on the recently emerged Sunda Shelf. (6) The most distinct subspecies, including all borderline cases between subspecies and species, are found along the periphery of the species range or at other very isolated locations. (7) Double invasions of the same parental stock have led either to the existence of two sympatric species, as are D. montanus and D. hottentottus leucops on Celebes, and on the Andamans D. andamanensis and D. paradiseus otiosus, or to the formation of hybrid flocks (D. caerulescens and D. paradiseus on Ceylon). (8) Two species groups, adsimilis and hottentottus, freely colonize oceanic islands. The other species, though not differing in their physical equipment, are limited to continental shelves and a few nearby islands.

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