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Identification of Adult Male Rufous and Allen's Hummingbirds, with Specific Comments on Dorsal Coloration

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Identification of Adult Male Rufous and Allen's Hummingbirds, with Specific Comments on Dorsal Coloration IDENTIFICATION OF ADULT MALE RUFOUS AND ALLEN'S HUMMINGBIRDS, WITH SPECIFIC COMMENTS ON DORSAL COLORATION PAUL M. McKENZIE,U.S. Fishand WildlifeService, 608 E. CherrySt., Room 200, Columbia, Missouri65201 MARK B. ROBBINS,Division of Ornithology,Natural History Museum, University of Kansas,Lawrence, Kansas 66045-2454 Our understandingof the statusof vagranthummingbirds across eastern North America has changed dramaticallyover the past three decades (Conway and Drennan 1979; see fall and winter seasonalreports in American Birds/Field !¾otes).Although an increasein hummingbirdfeed- ers and observers'expertise undoubtedly has contributedto our knowledge of extralimitalhummingbirds, Hill et al. (1998) hypothesizedthat the significantincrease in transient and wintering Rufous Hummingbirds (Selasphorusrufus) in the East is primarilya resultof a relativelyrecent changein thishummingbird's innate migratory behavior. Regardless of the reason(s),not all Selasphorushummingbirds in the easternUnited States have been Rufous;banding and in-handmeasurements have documented Allen's (S. sasin) in several states east of the Rockies (Newfield 1983, Andrewsand Baltosser1989, Stedman1992, Grzybowski1993, Jackson 1993, Davis 1994, Texas OrnithologicalSociety 1995). There are now more than 15 recordsfor this speciesin both Mississippiand Alabama(R. Sargentpers. comm.). The conventionalfield charactersfor distinguishingadult males of the Rufousand Allen'shummingbirds have been dorsal coloration and aggression displays:the Rufoushas a rufousback and an ovaldisplay flight, whereas Allen'shas an all-greenback and an "archingpendulum-like (•- J-shaped)" courtshipdisplay (Pough 1957, Johnsgard1983, National Geographic Society 1983, Peterson1990). These authors,however, apparently over- lookedcautionary statements in the literatureabout the dorsalcoloration of adultmales. An exhaustivecompilation of molt,age, and identificationcriteria for hummingbirdsdoes not mentionthe possibilityof mostlyor whollygreen- backedadult male RufousHummingbirds (Pyle 1997). LoyeMiller (in Willett 1933) wasthe firstto statethat someadult male Rufous Hummingbirds have entirelygreen backs.Phillips et al. (1964) reiteratedthis same point, and Phillips(1975) specificallymentioned a wholly green-backedadult male specimenthat he identifiedas a RufousHummingbird. More recenfiy, Kaufman (1990) underscoredthat dorsal colorationof adult males is not diagnostic,and he advancedthe notionthat Allen'sis not identifiableunder fieldconditions away from its breeding grounds. Because none of thesepapers presentedsupportive data, coupled with manyauthors' apparent oversight of this literature,the merit of back colorationas a diagnosticfield character remainscontroversial. Therefore, some ornithologists and statebird records committeeshave been reluctant to acceptfield identifications of adultmales of thesetwo specieswithout additional measurements obtained in the hand (see Langridge1988, Lasleyand Sexton 1991, Lasleyand Sexton 1992). In this 86 WesternBirds 30:86-93, 1999 IDENTIFICATION OF ADULT MALE RUFOUS AND ALLEN'S HUMMINGBIRDS paperwe addressvariation in the backcolor of adultmale Rufous and Allen's hummingbirdsand its bearingon fieldidentification. METHODS We examined202 specimensof adultmale Rufous and Allen'shumming- birdsfrom 14 museumsand universities(see Acknowledgments for list of institutions).All specimenshad completegorgets with the lateralfeathers elongated(Pyle 1997, fig. 99H) and lackedbill corrugations(Ortiz-Crespo 1972,Yanegaet al. 1997). Thereforewe presumedthem to be in at leasttheir secondcalendar year (Pyle 1997). Robbinsmeasured wing chord (unfiattened), tail length(central rectrices), exposed culmen, and width of the fifth (outer- most)rectrices with calipersto the nearest0.1 mm. Althoughwe measured the width of rectrix 1 (central),we considerthis characterto be too variable, becauseit varies considerablyas the result of how the specimenwas prepared.We excludedspecimens lent by the Museumof VertebrateZoology, Universityof California(15 specimensof each species),from our morpho- logicalanalysis so that our samplewould be independentof Stiles'(1972). Our examinationof 153 adultmale specimensof the RufousHumming- birdclearly demonstrated a continuumin dorsalcoloration from individuals with almostentirely rufous backs (most have a few greenfeathers) to those with entirelygreen backs (Figure 1). To minimizethe inclusionof potential hybrids,we analyzedspecimens with <50% and >50% of the backgreen separately,using only those with <50% of the backgreen to characterizethe measurements of the adult male Rufous. We characterized adult male Allen's with specimensof the nominatesubspecies only; all of thesespecimens had entirely green backs. We excludedsubspecies sedentarius because our sampleof it wassmall; however, as Stiles (1972) notedand our inspection of nine specimensalso indicated, the onlydifference between the two subspe- ciesis culmenlength. RESULTS Our measurements of the 125 adult male Rufous with <50% of the back green and 28 Allen's are very similar to Stiles' (1972) (Table 1). As mentionedabove, Stiles' sample (30 individuals/species)was independent of ours. In additionto the significantdifference in the width of rectrix 5 (outermost)(Table 1; t test = 16.14, df = 148, P < 0.025), we found that adultmale Rufoushave longerwings (t test = 13.78, df = 150, P < 0.025) andtails (t test = 16.08, df = 149, P < 0.025) than adultmale Allen's.In our samples,the two species'exposed culmen lengths did not differstatistically (t test = 1.19, df = 137, P > 0.05). In none of the 125 Rufousspecimens with <50% of the back green did measurementssuggest hybridi•:ation. Furthermore,all malesin thisgroup had the "deepemargination" at the tip of rectrix2 characteristicof adultmale Rufous(Stiles 1972; Figure2). All 28 specimensused for defining the measurementsof Allen's had a non- emarginatedtip on rectrix 2. Of the 16 Rufous with >50% of the back green, only three have characterssuggesting they may be hybrids(Table 2). Ironically,the specimen 87 IDENTIFICATION OF ADULT MALE RUFOUS AND ALLEN'S HUMMINGBIRDS Figure1. Variationin dorsalcoloration of adultmale RufousHummingbirds from all greento all rufous.Specimens (from left to right):UAM 5664, CMNH 115470. MVZ 5411. UW 38697, and LSUMZ 40256. that Phillips(1975) reportedas an adultmale Rufouswith an all-greenback is likelya hybrid.Although he did not cite the numberof the specimentaken at San FranciscoPeaks, north of Flagstaff,Arizona, on 26 July 1969, it is obvious that Northern Arizona University 708 is the specimen. This spe½imen'swing length,40.5 mm, and widthof the fifth rectrix,2.6 mm, fall within the variationfor Rufous.whereas the tail length. 23.5 mm. is short even for adult male Allen's (Table 1); however,the very tip of the tail is somewhatworn. Unfortunately.several millimetersof the tips of both second rectrices are missing, apparently destroyedwhen the bird was collected,precluding assessment of this importantcharacter. We foundtwo other likelyhybrids. One, collectedon 28 February1937 at Yuma, Arizona (San Diego Natural History Museum[SDNHM] 17485). has an all-greenback and the wing length (38.7 mm) of Allen's. Its tail length (26.6 mm), however,is intermediate.Furthermore, the shapeof the tip of the right rectrix 2 (the left is missing)is also intermediate--it is slightly emarginated.A secondbird (LouisianaState UniversityMuseum of Natural Science[LSUMZI 89623), taken on 6 January 1979 at Metairie, Jefferson Parish, Louisiana, was initially identified as a hybrid Rufous x Allen's (Hamilton 1979). but A. R. Phillipslater annotatedthe specimenas an Allen'swith the tip of rectrix2 anomalouslyemarginated. We suspectthat LSUMZ 89623 is a hybridbecause its rectrix 2 is even more emarginated thanthat of SDNHM 17485. The wingchord (38.0) fallswithin the variation of Allen's; however, the wings are badly worn. But the tail is in good conditionand is intermediate(25.7) in length (Table 1). 88 IDENTIFICATION OF ADULT MALE RUFOUS AND ALLEN'S HUMMINGBIRDS Table I Measurements (mm) of Adult Male Rufousø and Allen'sb Hummingbirds This study Stiles(1972) n Mean SD c n Mean SD Wing length(chord) Rufous 124 40.62 0.87 30 40.32 0.87 Allen's 28 38.11 0.89 30 38.08 0.84 Tail length Rufous 123 27.90 0.90 30 27.36 0.91 Allen's 28 24.96 0.74 30 24.37 0.74 Width of rectrix5 (outer) Rufous 123 2.64 0.29 -- -- -- Allen's 28 1.70 0.20 -- -- -- øSpecimenswith <50% of the backgreen only. bSubspeciesSelasphorus sasin sasin only. CStandard deviation. Figure2. Tailsof adultmale Allen's(right) and Rufous(left) hummingbirds. Compare the width of the fifth rectrices(outer): narrow in Allen's versusrelatively broad in the Rufous.Also note the differencein the shapeof the tip of rectrix2: nonemarginated in Allen's versusnotched or emarginatedin the Rufous. 89 IDENTIFICATION OF ADULT MALE RUFOUS AND ALLEN'S HUMMINGBIRDS Finally,although our samplesizes from the breedingrange are small,we foundno geographicalcomponent to the amountof green on the back of adultmale RufousHummingbirds. Breeding birds near the zone of contact with Allen'sin southwesternOregon and northwesternCalifornia show no increasein green on the back. DISCUSSION Our resultsreveal considerablevariation in back color, from all rufousto entirelygreen, in adultmale Rufous Hummingbirds (Figure 1). In our sample of 153 presumedpure RufousHummingbirds, seven (5%) havethe backat least75% green,and two havethe back95-100% green(Table 2). ThusMiller (in Willett1933), Phillipset al. (1964), and Kaufman(1990)
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