(Aves: Trochiiidae). 5. Probable Hybrid Origin of Amazilia Distans Wetmore & Phelps
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6 April 1998 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON 111(1)28-34 1948. Diagnoses of hybrid hummingbirds (Aves: Trochiiidae). 5. Probable hybrid origin of Amazilia distans Wetmore & Phelps Gary R. Graves Depart men I of Vertebrate Zoology. National Museum of Natural History, Smithsonian Institution. Washington. DC. 20560, U.S.A. Abstract.—Amazilia distans Wei more & Phelps, 1956, is believed to be a hybrid between Hylocharis eyamts and Amazilia fimbriata. The hybrid, col- lected in Estado Tachira. Venezuela, exhibits a blended mosaic of plumage characters of the parental species. External measurements of the hybrid fall between the character means; of the parental species which overlap in size. The unique holotype of Amazilia distans attributed to mutation or developmental Wetmore & Phelps, 1956 was collected by variation of any known taxon. Nor does it Ramon Urbano at "El Salao" (300 m) near seem to represent a morphologically dis- Burgua, Estado Tachira, Venezuela, on 17 tinctive or geographically isolated popula- July 1954. Originally deposited in the Co- tion of another species of Amazilia. Con- leccidn Omitologica Phelps (No. 60790). sequently, A. distans appears either to be a Caracas, the type was cataloged on 9 Oc- valid species or a hybrid. As hybrids have tober 1956, in the National Museum of Nat- no standing in zoological nomenclature, the ural History (USNM 461695), Smithsonian burden of proof lies with the taxonomist to Institution. Collar et al.'s (1992) report of a reject conclusively the hybrid origin of A. second specimen in the Coleccion Phelps distans before bestowing species status on was based on a misreading of the Phelps it. I was unable to reject I he hypothesis of card catalog (fide M. Lentino, N. Collar). hybridity. References treat A. distans as a valid spe- Hybridization between species from dif- cies (e.g.. Morony et al. 1975, Meyer de ferent subfamilies, Phaethornithinae and Schauensee & Phelps 1978, Hilly & Brown Trochilinae. is unknown (Graves 1990). As- 1986. Sibley & Monroe 1990, Collar et al. suming a hybrid origin for A. distans, the 1992). Analyses reported here suggest that pool of potential parental species ( = geo- it represents a hybrid between Hylocharis graphic pool) can be limited to the species cyanns and Amazilia fimbriata. I provide a of trochiline hummingbirds (« — 23; see detailed hybrid diagnosis employing the Appendix 1) that occur regularly below methods and assumptions outlined in 1000 m elevation in the region immediately Graves (1990) and Graves & Zusi (1990). south and east of the Andes in Estado Tach- ira and Estado A pure. Venezuela (Phelps & Materials and Methods Phelps 1958, Meyer de Schauensee & Phelps 1978. Hilty & Brown 1986). 1 com- The holotype of Amazilia distans was pared A. distans directly with specimens of sexed as male (testes drawn on original la- all hummingbird species in the collections bel). The unstriated maxillary ramphotheca of the National Museum of Natural History. (see Ortiz-Crespo 1972) and brilliant plum- Smithsonian Institution, paying particular age of the specimen indicate that it is an attention to those listed in Appendix 1. adult in definitive plumage (Pigs. 1, 2). The Notes, photographs, and videotape of the unique appearance of A. distans cannot be holotype were compared with the extensive VOLUME III. NUMBER I 29 table I.—Ranges and means (± one standard ile- ferred to as a hybrid in the remainder of viation) of measurements (mm) of representative spec- this paper. imens i.i.liilr male) of Hylm-harix cyanus, Amazitutfim- lustiiii, and the Hybrid, Hylwhans cvanus x Amazilia fiinhriaia i= Amazilia distorts Wctmore & Phelps. Results and Discussion 1956: USNM 461695). Several characters of the hybrid permit fi'tih mil*! in = I*) Hybrid its parental species to be identified: (a) bill red tipped with black in life; (b) base of bill Win^ ehord 47.1-53.0 52.4-56.5 51 0 49.8 ±15 54.7 t 1.4 conspicuously swollen, nasal flanges un- Bill length 14.8-18.5 17,3-22.0 IS,6 feathered and exposed; (c) crown glittering 16.9 ± I.I 19,8 ± 1.3 bluish-green; (d) throat glittering bluish- Reetrix 1 24.1-27.4 26.2-30.1 26.6 green, chin and upper throat streaked with 25.9 i 1.2 28.8 ± 1.0 white; (e) indistinct white pectoral spot; (f) Reetrix 5 25.1-28.1 27.7-32.5 27.4 26.7 ± 1.0 30.6 ± 1.4 abdomen gray along midline; and (g) rec- trices black, innermost and outermost about •Colombia <n = 5). Venezuela (n = 4), Guyana the same length (Appendix 2; Fig. I, 2; Ta- (n = 3) ble 1). None of the potential parental spe- "Colombia (n = 8), VenezueJa (n = 8). cies considered one at a time exhibits this suite of character states in definitive or sub- definitive plumage. series of Amazilia and Hylocharis in the The red bill of the hybrid appears to be American Museum of Natural History. New the most useful character for initially nar- York. rowing the held of potential parental spe- Color descriptions were made under Ex- cies. Adult males of several species in Ap- amolites (MacBefh). Measurements of wing pendix 1 have pink or red mandibular (low- chord, bill length (from anterior extension er jaw) ramphothecae (Lophornis delattrei, of leathers), and reetrix length (from point L. stictolophus, Chrysumnia oenone, Hy- of insertion of the central rectrices to the tip locharis cyanus, Amazilia versicolor, A. of central and outermost rec trices) were fimhriata, and A. viridigaster), and some taken with digital calipers and rounded to specimens of A. fimbriata have pinkish- the nearest 0.1 mm (Table 1). Measure- brown maxillary ramphothecae (upper jaw). ments and least squares regression lines However, bright red maxillary ramphothe- were projected on bivariate plots to illus- cae are found in only three species, L. de- trate size differences (Wilkinson 1989). lattrel, L. stictolaphus, and Hylocharis cy- The hybrid diagnosis was approached in anus. Lophornis can be eliminated as pos- a hierarchical manner. The presumed paren- sible parents of A. distans because they tal species of A. distans were hypothesized possess elongated rufous crests and pre- through the comparative analysis of plum- dominately rufous rectrices. which would age pattern and color, feather shape, and bill almost certainly be expressed in a hybrid. colon As a second step, the restrictive hy- Hylocharis cyanus is thus identified as the pothesis was tested with the quantitative parental contributor of the red maxillary analysis of size and external proportions. raniphotheca of the hybrid. Concordance of results is regarded as Identifying the second parental species is strong support for the hypothesis (Graves most easily accomplished by focusing on 1990, 1993a, 1993b, 1996a; Graves & Zusi the plumage characters of the hybrid that 1990). Atavism or hybrid luxuriance has are lacking in Hylocharis cyanus. Plumage not been demonstrated in hybrid humming- of the head, chin, throat and upper breast birds (Banks & Johnson 1961. Graves of H. cyanus is glittering purple. The in- 1990). For brevity. A. distans will be re- heritance of iridescence in hybrid hum- \0 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON Fig, I. Lateral and ventral views of male Amazilia fimhriam (top), Hylmhuris cyanus (bottom), and llieir putative hybrid, A. dhtans Wetmore & Phetps (USNM 461695I, VOLUME 111, NUMBER 1 33 Fig. 2. Lateral view of head and hill of the type of AmuzitUt distorts Wemiore & Phelps (USNM 4AloV5). mingbirds is poorly understood (Graves undertail coverts), Chalybura buffonii 1990, Graves & Zusi 1990). In this case, (lengthened silky white undertail coverts). however, I assume that hybridization be- Heliomaster (ongirostris (tail spots, brilliant tween two purple-crowned species would magenta gorget). Thalurania furcata (pur- not result in offspring with a bluish-green ple lower breast, deeply forked tail), Heiiu- crown. The glittering bluish-green crown doxa leadbeateri (violet crown patch), Ster- and throat of the hybrid suggest that the noclyta cyanopectus (violet breast patch, second parental species has iridescent green white-tipped rectrices, heavy curved bill), plumage in these areas, ruling out Klais Coeligena coeligena (brown plumage), guimeti (purple chin and upper throat) as a Ocreatus underwoodii (racket-tipped rectri- parental species. In another example, the ces, tibial "puffs"), Agtaiocercus kingi rectrices of Chrysuronia oentme are shining (greatly elongated rectrices with metallic coppery-gold on both dorsal and ventral bluish-green dorsal surfaces), and Chaeto- surfaces, whereas the rec trices of the hybrid cercus jourdanii (rufous shafts of rectrices. are black, similar to those of H. cyanus rose throat), can be removed from the list (bluish-black). Hybridization of C. oenone of potential parental species because they and H. cyanus would likely produce off- exhibit plumage characters not expressed in spring with bronze-colored or dark brown the hybrid. By the process of elimination, rectrices that are significantly paler, less the second parental species appears to be melanized, than those of the hybrid. In a one of three species of Amazitia that are similar fashion. Campy lopterus falcatus sympatric with Hylocharis cyanus in Taeh- (chestnut rectrices, thickened primary ra- ira. Venezuela (Appendix I). chises), Colibri thalas.tinus and C. corus- Wetmore & Phelps (1956:4) noted that cans (purple auricular tufts, banded rectri- the type of A. distans had the general ap- ces), ChtorostHbon poortmani (shining pearance of Amazjlia fimbriata. differing golden-green tail), Chlorestes notatus (bril- from that species "in the glittering blue liant bluish-green plumage from breast to foreneck and upper breast, and in possess- 32 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON 22 A A V . 20 A ^0*^• A A *f*A IB - • • ** A ^--* • s 16 * * 24 26 28 30 32 34 Length Reclrn 5 Fig. 3. Bivariatc plots of selected measurements (see Table 1) of mate Hyttxharis cyanus (diamonds I.