PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON 112(3):491-502. 1999. Diagnoses of hybrid hummingbirds (Aves: Trochilidae). 8. A provisional hypothesis for the hybrid origin of Zodalia glyceria (Gould, 1858) Gary R. Graves Department of Vertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560, U.S.A. Abstract. — Zodalia glyceria (Gould, 1858), supposedly from the vicinity of Popayan, Colombia, is hypothesized to be a hybrid between Lesbia victoriae and Chalcostigma herrani, which are sympatric in shrublands and timberline ecotones in the Andes from southern Colombia to northern Peru. Those por-tions of the capital, spinal, and ventral feather tracts that exhibit green irides-cence in the parental species are greenish-blue to purple in the hybrid, de-pending upon the angle of observation. For example, the dominant wavelength reflected from back plumage is much shorter in the hybrid (505 nm) than in either of the parental species (561-576 nm). This color shift is thought to have been caused by a developmental aberrancy, possibly associated with hybrid-ization, which affected melanin granules that produce iridescence in feather keratins. Rectricial measurements of the hybrid fall between the character means for L. victoriae and C. herrani whose tails differ markedly in shape. Among the many puzzling species of hummingbirds described by John Gould, Cometes glyceria stands apart in taxonomic obscurity (Gould 1858: opposite plate 176): "During the many years that I have given atten-tion to the Trochilidae, I have not met with a bird which has caused me more thought, and I may say perplexity, ... it is intimately allied to the members of the genera Lesbia, Cometes and Cynanthus, par-taking as it does, either in form or colouring, of characters pertaining to each of those genera. Some-times it has occurred to me that it might be a hybrid between either two of them, but I am perfectly at a loss to say which two species would be likely to produce such a cross. Such an idea has entered my mind, but when I have again and again reconsidered the matter, it has appeared to me that it is a distinct species, and that it may ultimately prove to be the female or young male of some gorgeous bird with which we are at present unacquainted." As a consequence of evolving generic definitions, glyceria was placed first in Sparganura (Cabanis & Heine 1860, Scla-ter & Salvin 1873) and later transferred to Zodalia (Mulsant & Verreaux 1876, Elliot 1878, Salvin 1892, Boucard 1893, Sharpe 1900, Oberholser 1902, Cory 1918). Simon (1921) considered Zodalia glyceria to be a senior synonym and immature plumage of Z. ortoni (Lawrence 1869), a position em-braced by Peters (1945). The taxonomic va-lidity of Zodalia glyceria was not formally challenged until Meyer de Schauensee (1947) declared both Z. glyceria and Z or-toni to be hybrids of Lesbia victoriae and Ramphomicron microrhynchum. This con-clusion was followed by subsequent authors (e.g., Morony et al. 1975, Greenway 1978, Fjeldsa & Krabbe 1990, Sibley & Monroe 1990, Collar et al. 1992). Meyer de Schauensee's (1947) evaluation of Z ortoni appears to be valid (Graves 1997); however, the holotype of Zodalia glyceria seems to represent a different, and previously unre-ported, intergeneric hybrid. Here I provide a detailed hybrid diagnosis employing the methods and assumptions outlined in Graves (1990) and Graves & Zusi (1990). In recognition of its 120-year association
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