ISSeptembci 1998 PROCEEDINGS OF THK BIOLOGICAL SOCIETY OF WASHINGTON 1IK3):511-520. 1998. Diagnoses of hybrid hummingbirds (Aves: Trochilidae). 6. An intergeneric hybrid, Aglaiocercus kingi x Metallura tyrianthina, from Venezuela Gary R, Graves Department of Vertebrate Zoology. National Museum of Natural History. Smithsonian Institution. Washington, DC. 20560. U.S.A. Abstract.—An intergeneric hybrid hummingbird. Aglaiocercus kingi X Me- tallura tyrianthina. is described. External measurements of the hybrid are in- termediate of those of the parental species. Back plumage iridescence is bluer {511 nm) in the hybrid than in either of the parental species (553-571 nm). This color shift is thought to he caused by a developmental aberrancy or mu- tation which affects melanin granules thai produce iridescence in feather ker- atins. Under certain circumstances, interspecif- Here I describe an intergeneric hybrid com- ic hybridization may be an important source bination, Aglaiocercus kingi x Metallura of genetic exchange among avian lineages tvriaiuhina. that may create favorable conditions for rapid and significant evolutionary change Materials and Methods (Grant & Grant 1992). From an analysis of data in Panov's (1989) catalog of avian hy- The unsexed specimen (American Mu- brids. Grant & Grant (1992) reported that seum of Natural History [AMNH] 146645) 19,1% (6t of 319) of hummingbird species was collected by S. Gabaldon in Esiado has hybridized in nature. A surprising Men da. Venezuela. The exact locality, ele- 69.2% (36 of 52) of the hybridizing pairs vation, and date of collection are unknown. is intergeneric (taxonomy of Sibley & Mon- The specimen appears to he a male in sub- roe 1990). a finding consistent with Prager definitive plumage as evidenced by the I aim & Wilson's (1975) thesis thai interspecific strialions on the maxillary ramphotheca hybridization potential is slowly lost during (see Ortiz-Crespo 1972) and by its elongat- avian evolution. The true extent of hybrid- ed tail (Fig. 1 & 2). Five different identifi- ization among hummingbirds, however, is cations have been written in ink and pencil imperfectly known. Panov's (1989) compi- (in quotations below) on the two attached lation includes numerous poorly document- AMNH labels since the specimen was cat- ed or erroneous records, as did its antece- aloged in 1927 (in probable order of occur- dent (Gray 1958). Moreover, many new hy- rence): (a) "Cyanolesbia" [—Aglaiocer- brid combinations have been reported re- cus]: (b) "Aglaiocercus Icaudata" cently (e.g.. Graves 1990, 1996a, 1998a: [=Aglaiocercus kingi caudatux]: (c) "Me- Graves & Zusi 1990: Hinkelmann 1996: rallura purpureicauda" [ = Chalcostigma Welter & Schuehmann 1997). A definitive purpureicauda]: (d) "?Hybrid?, Aglaiocer- analysis of hybridization and phyletic retic- cus caudata X Ramphomicron" [=Agtaio- ulation must await a robust phylogeny and cercus kingi caudarus X Ramphomicron a systematic survey of purported hybrids, microrhynchum\\ and (e) "Aglaiocercus type specimens, and museum collections. emmae caudata, (melanistic aberration), 512 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON Fig. 1. Vciural views of mule Agtaiocenux kingi ctiudittux I lop 1. Metullurtt tyritmthinu oreopoiu (bottom), and a probable hybrid, A. kingi caudatus x M. ryrumihina oreopolti (AMNH I46h45). Fig. 2, Probable hybrid. AgUuocerais kingi caudatus X Metallura lyrimuhina onapofa (AMNH I4h(vt5j. VOLUME 11). NUMBER 1 513 fide J. Berlioz, Apr. 1975" \=Ag!aiocercus ues are dark, high values are light. In other kingi caudattts]. words, the more light reflected from the I compared the oft-identified specimen plumage the higher the L value will he. It with series of all species in the subfamily should be noted that visual systems in hum- Trochilinae, the typical hummingbirds (Zusi mingbirds (e.g.. Goldsmith & Goldsmith & Bentz 1982. Sibley & Monroe 1990. 1979) differ significantly from those of hu- Bleiweiss el al. 1997), in the collections of mans. The relevance of opponent color co- the American Museum of Natural History ordinates to colors perceived by humming- and the National Museum of Natural His- birds is unknown. Dominant wavelengths tory (USNM), Smithsonian Institution. For re lice ted from plumage surfaces are listed the purpose of hybrid diagnosis. I consid- for comparison. Data in Table I were com- ered all hummingbirds (Trochilinae: taxon- piled from the averages of five independent omy of Sibley & Monroe 1990) that occur measurements (specimen moved from ap- in Estado Merida as potential parental spe- erture between trials) for each plumage area cies {Phelps & Phelps 1958, Meyer de per specimen. Schauensee & Phelps 1978) (Appendix I). Measurements of wing chord, bill length In addition, I compared the specimens di- (from anterior extension of feathers), and rectly with the hoiotypes of Chalcostigma rectrix length (from point of insertion of the purpureica uda (A M N H 483931), Lesbia central rectriccs to the tip of each rectrix) ortoni (AMNH 156651), Zodalia thattmas- were taken with digital calipers and round- ta (USNM 173911), and Aeronympha pro- ed to the nearest 0.1 mm (Table 2). Mea- xantis (Field Museum of Natural History, surements and least squares regression lines FMNH 11852), and with notes, photo- were projected on bivariate plots to illus- graphs, and videotape of the holoiype of trate size differences (Wilkinson 1989). Hefiangelus zuxii (Academy of Natural Sci- There are three alternatives to consider- ences of Philadelphia, ANSP 159261). the specimen represents an aberrant color Color descriptions given in Appendix 2 morph of A. kingi or some other species, a were made under natural light. 1 evaluated hybrid, or an tmdescribed species. The the color of dorsal plumage (center of back) specimen differs significantly in size and and the ventral surfaces of the rectrices with shape from all species in Appendix I. In a reflectance spec trap ho to meter equipped particular, the rec trices of the specimen are with a 11.0 mm aperture (Color Mate Col- considerably wider, flatter in cross section, orimeter. Milton Roy). The colorimetric and more iridescent on the ventral surfaces characters were described in terms of op- than in A. kingi, indicating that it is not sim- ponent-color coordinates (L, a, b) (Hunter ply a melanistic example of that species as & Harold 1987). This system is based on suggested by Berlioz on the specimen label. the hypothesis that signals from the cone Because hybrids have no standing in zoo- receptors in the human eye are coded by the logical nomenclature, the burden of proof brain as light-dark (L), red-green (a), and rests on the investigator to refute this pos- yellow blue (/;). The rationale is that a color sibility before bestowing species status on cannot be red and green or yellow and blue a unique specimen. Because the evidence at the same time. Therefore "redness" and points to hybridization, I refer to the spec- "greenness" can be expressed as a single imen as a hybrid in the remainder of the value a, which is positive if the color is red paper. and negative if the color is green. Likewise, The diagnosis was approached in a hi- "yellowness" or "blueness" is expressed erarchical manner. The presumed parental by b for yellows and —b for blues. The species of the hybrid first were hypothe- third coordinate L, ranging from 0 to 100, sized through the comparative analysis of describes the "lightness" of color; low val- plumage pattern, as well as from feather 514 !>RC>| I I DINliS , »l THI UK II OCJICAl. SUClliTY OI- WASHINGTON Table I.—Ranges and means (rstandard deviation) of opponent color coordinates (L a. b) and dominant wavelength reflected from dorsal plumage (enter of back) and the venmil surface of reel rices in male Aglaio- cercus kingi ctmcJtilits. Mrlallum tyriamhinu orwpttitt. and their probable hybrid (AMN'H 146645). M Ivntinltiiuii Vtritbta (n - IZ hi - IZ) IMmJ Back plumage L (LightNcssi (i) 23.6-30.1 21.5-26.6 24,1 27.1 ± 1.8 24 2 r 1.4 a (Red | + |/Grcen [-]) (a) - l4.8-(-6.6) -7.l-t-0.6l -7.9 - 10.9 + 2.9 -3.7 ± 1.8 t (Yellow [+yBkie (-]> (A) 15.4-20.2 12.6-20.9 2.9 17.8 t 14 17.3 ± 2.3 Dominant Wavelength Inml 553.1-563.8 562.8-570.5 511.3 557.8 ± 3.5 566.7 ± 2.6 Ventral surface of reel rices t (Lightness) CM 18.8-21.1 20.3-23.9 20.6 20.1 ± 0.7 21,7 ± 1.0 a (Red [ +(/Green [-)) fa) 3.8-5.9 11.5-17.0 10.6 4.9 ± 0.6 14.6 ± 1.6 ft (Yellow | +I/Blue (-]) (*) -4.3-1.5 5.5-14.9 -7.1 -0.9 ± 1.9 9.5 ± 2.9 Dominant Wavelength Inm) 487.2-652.1 588.9-622.7 541.0 520.7 ± 47.7 602.5 ±11.2 and bill shape. The restrictive hypothesis port for the hypothesis (Graves 1990. then was tested with a quantitative analysis Graves & Zusi 1990). of size and external proportions. Concor- dance of results is regarded as strong sup- Results and Discussion Plumage characters,—Salient characters Table 2.—Ranges and means (±standard deviation) of the hybrid that permit its parental species of measurements (mm) of males of Agkiiinvnus kingi to be identified include: (a) moderately caudatus isuhdefinitive plumage, see Appendix 2). elongated outer rectrices (fork depth = 23.7 Metatlura lyritintfiino oreapola. and their presumed hvhrid(AMNH 146645). mm), nearly flat in cross section; (b) un- marked rectrices exhibiting metallic irides- M (ynnnttiiint cence on the dorsal and ventral surfaces; (c) Chaiaurr (n »3t) Ml HyhnJ short tibial plumes (not extending to hal- Wing chord 59,7-63.6 54.0-61.5 61.4 lux); and (d) short straight bill (11.1 mm). 61.8 ± 1.0 57.7 * 2.2 Two species in the pool of potential paren- Bill 11.0-13.6 9.1-10.6 11.