. Bulletin of the British Ornithologists' Club. some islands. The high proportion of intermediate birds indicates consider- able successful breeding and genetic recombination. Perhaps some differen- tiation of the herons occurred on different islands with subsequent inter- island reinvasion and interbreeding, or more likely the islands were invaded successfully by more than one wave of immigrants from South America in the past: either history might account for the variation among the Galapagos herons. The Galapagos herons are variable, but nearly all adults are separable from adults of the con
. Bulletin of the British Ornithologists' Club. some islands. The high proportion of intermediate birds indicates consider- able successful breeding and genetic recombination. Perhaps some differen- tiation of the herons occurred on different islands with subsequent inter- island reinvasion and interbreeding, or more likely the islands were invaded successfully by more than one wave of immigrants from South America in the past: either history might account for the variation among the Galapagos herons. The Galapagos herons are variable, but nearly all adults are separable from adults of the continental populations. The Lava Heron is probably best considered a distinct subspecies, B. striatus sundevalli, at least until studies on breeding pairs have been made in the islands. Acknowledgements: For loaning or providing access to their material I thank W. E. Lanyon, J. Farrand, and J. J. Morony (American Museum of Natural History), L. C. Binford (California Academy of Sciences), R. L. Zusi (Nation- al Museum of Natural History), and M. A. Traylor (Field Museum of Natural History). I thank the F. M. Chapman Memorial Fund for support. L. C Binford, E. Eisenmann, K. C. Parkes, R. W. Storer, and A. Wetmore read the manuscript and offered helpful criticism. The figures were drawn by Patricia J. Wynne. References: Amadon, D. 1953. Avian systematics and evolution in the Gulf of Guinea. Bull. Amer. Mus. Nat. Hist. 100: 393-452. Bangs, O. 1915. Notes on dichromatic herons and hawks. Auk 32: 481-484. Bock, W. J. 1956. A generic review of the family Ardeidae (Aves). Amer. Mus. Novit. 1779. Eisenmann, E. 1952. Annotated list of birds of Barro Colorado Island, Panama Canal Zone. Smiths. Misc. Coll. 117(5): 1-62. — 1955. The species of Middle American birds. Trans. Linn. Soc. 7. Griscom, L. 1929. A collection of birds from Cana, Darien. Bull. Mus. Comp. Zool. 69: 147- 1190. Harr s, M. P. 1973. The Galapagos avifauna. Condor 75: 265-278. Hartert, E. 1920. Gattung Butorides Blyth
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