AGE AND SEX DETERMINATION IN THE CALLIOPE

WILLIAM H. BALTOSSER,Department of Biology,University of Arkansasat Little Rock, 2801 SouthUniversity, Little Rock, Arkar•sas72204

The informationavailable to distinguishadult female and youngCalliope (Stellu la ca11iope) is incomplete.Using any one of the many fieldguides currently on the market,one can identifyadult males with ease, butadult females and young often present more of a problem.Few attempts have been made until now to separateadult females from youngbirds of either sex becausethe technicalinformation this requireshas not been available.Such knowledge is particularlycritical given the increasingnum- ber of peoplelicensed to captureand bandbirds and the need to document properlythe growingnumber of vagranthummingbirds. Of the major worksdealing with hummingbirdidentification, relatively few have dealt with the Calliope Hummingbird.Elliot (1881), Ridgway (1892, 1911), Coues(1903), andJohnsgard (1983) all notedthe diagnostic shape of the middle rectrices, contracted in the middle and wider subterminally,i.e., somewhatspatulate or pandurate.Banks and Johnson (1961) addressedidentification as it relatesto presumedhybrid adult males, while Stiles(1971) providedcriteria allowing one to distinguishboth male and femaleCalliope Hummingbirds from other species. Stiles' (1971) criteria to separateCalliope Hummingbirdsfrom other hummingbirdspecies include small size, very short bill, and a short, broad tail containingvery little rufous. He also cited behavioralmannerisms, particularlythe positionof the tail while the is hovering(nearly perpendicularto the plane of body)and the degreeof tail movement(held very still). The barbs of the rectrices(stiflened and flattened)differ from those of other species,as do many standardmeasurements. Stiles was unable, however,to find consistentplumage differencesbetween adult femaleand youngCalliope Hummingbirds. It can now be shownthat there are consistentdifferences allowing distinction between young of either sex and adultfemales from young.

METHODS

! collectednumerous Calliope Hummingbirds over a ten-yearperiod and, through dissection,aged and sexed them. Having establisheda set of criteriafor identification,! expandedmy samplesize throughthe use of museum specimens. Ortiz-Crespo(1972) developedand I (Baltosser1987) further refineda method for aging hummingbirdsbased on the presenceand extent of corrugationson the bill.!n juvenilebirds, bill corrugations are obvious,being deeplyincised and extending the lengthof the bill.This is in sharpcontrast to the billsof adultbirds, which lack corrugations and appear to be smoothly polished.Corrugations in subadultbirds are shallow,confined to the baseof the bill, and often very faint; older subadultsmay lack corrugations(see Baltosser1987 for figures). 104 Western 25:104-109, 1994 CALLIOPE HUMMINGBIRD PLUMAGES

I usedbill corrugations as my primarymeans of agingCalliope Humming- birds,supplementing it to some extent by featherwear and plumage characteristics(e.g., bully featherfringes, often characteristicof young birds).The molt of CalliopeHummingbirds takes place on the wintering groundsin ,so in the U.S. bully-tippedplumage is generallyuseful to indicatehatching-year birds only during summer and fall. Measurementswere made with 10-cm dial calipers,accurate to the nearest0.05 mm. I testeddifferences among the age and sexclasses for statisticalsignificance with one-wayanalyses of variance(SAS Institute 1988). For each characterI calculated95% confidenceintervals about the mean. Quantitativemeasurements used to characterizehummingbirds were describedby Baldwinet al. (1931) and depictedby Baltosser(1987). I measuredthe lengthof the exposedculmen from its tip to the pointwhere

A B C D

E F G H

Scale

0 25 50 I , • I , , I I

Figure1. Diagnosticsize and shape of rectrix1 in the CalliopeHummingbird (sexes similar)compared to the sizeand shape of rectrix1 in other,potentially confusing, hummingbirdspecies (females only). A, Ruby-throated(Archilochus colubris); B, Black-chinned(A. alexandri);C, Anna's(Calypte anna); D, Costa's(C. costae);E, Calliope (Stellula calliope); F, Bumblebee(Atthis heloisa); G, Broad-tailed (Selasphorusplatycercus); H, Rufous(S. rufus)and Allen's (S. sasin). 105 CALLIOPE HUMMINGBIRD PLUMAGES the feathersof the foreheadimpinge on the culmen.Length of wing chord was measuredfrom the anterioredge of the wrist joint to the tip of the longestprimary (number10), withoutthe primariesbeing flattened.Tail length,only to the nearestmillimeter, was measuredfrom the insertionof the two middlerectrices to the longestfeather of the unspreadtail. The "area"of white at the tip of the thirdrectrix (rectrices numbered from center out)was calculated by multiplyingthe lengthof whitealong the rachisby its maximumwidth (seeBaltosser 1987).

RESULTS AND DISCUSSION

In femaleand youngCalliope Hummingbirds the size of rectrix 1 in conjunctionwith itsshape (expanded near the tip) is species-specific(Figure 1). In iramatures,the presenceof rufousalong the edgesof rectrix1 is

Subadult & Juvenile

Males

Rufous '•'••'' Green Black

Subadult & Juvenile

Females

Figure 2. Diagnosticcolor patternsof rectrix 1 distinguishingmale and female juvenileCalliope Hummingbirds. Three examples of eachto showrange of variation. 106 CALLIOPE HUMMINGBIRD PLUMAGES

TaBle 1 Measurementsof Adult CalliopeHummingbirds a

Exposed Wing culmen chord Tail (mm) (mm) (mm)

Male Mean 14.20 39.55 20.20 Standard deviation 0.35 0.70 0.90 N 10 10 10 Range 13.75-14.65 38.65-40.70 19-21 95% Confidence interval 13.95-14.45 39.05-40.05 19.55-20.85 Female Mean 15.40 42.00 21.80 Standard deviation 0.50 0.60 0.70 N 15 15 15 Range 14.65-16.35 41.05-43.30 21-23 95% Confidence interval 15.10-15.70 41.65-42.35 21.40-22.20

aDifferencesbetween males and femalessignificant in everycase (P < 0.05). diagnosticof males;absence of rufousis diagnosticof females(Figure 2). Adult females,however, like thoseof many other westernhummingbirds (Baltosser1987), showthe entirespectrum of variabilityin rectrix1, though they frequentlyexhibit at least some rufous. Sex determinationis thus complicatedand can be establishedonly after aging,which in summerand

Table •- Measurementsof JuvenileCalliope Hummingbirds a

Exposed Wing Whitetip culmen chord Tail rectrix 3 (mm) (mm) (mm) (mm2)

Male Mean 13.25 41.35 21.65 5.60 Standard deviation 0.50 0.90 0.75 2.00 N 16 15 14 16 Range 12.40-13.95 39.25-42.70 21-23 3.20-10.00 95% Confidence interval 13.00-13.50 40.85-41.85 21.20-22.10 4.55-6.65 Female Mean 14.55 43.70 22.75 17.95 Standard deviation 0.50 0.50 0.90 4.15 N 10 11 11 10 Range 13.80-15.20 42.85-44.30 21-24 11.35-26.50 95% Confidence interval 14.20-14.90 43.35-44.05 22.15-23.35 15.05-20.85 aDifferencesbetween males and femalessignificant in everycase (P < 0.05).

107 CALLIOPE HUMMINGBIRD PLUMAGES fallis accomplishedon the basisof billcorrugations, feather wear, and buff- tippedplumage (primarily that of the headand neck). Further complicatingidentification are adult femaleshaving iridescent rose-colored feathers on the throat. Such females are undescribed in popularfield guides; I confirmedtheir sexonly throughcareful dissection. Females with iridescentthroat feathers I presume, on the basisof their extensivelyworn billslacking corrugations, to be relativelyold. Fortunately, few birdsexhibit this conditionand their smalliridescent rose feathers only superficiallyresemble the brighterand broadergorget feathers frequently foundon youngmales. Measurementsof adultmales and femalesare presentedin Table1, those of immaturesin Table 2. Note that all comparisonsbetween adultsare significantlydifferent (? < 0.05), as are those betweenimmatures. In additionto differencesin standardmeasurements, young males and females are separableon the basisof the amountof white at the tip of the third rectrix.

CONCLUSIONS

In the CalliopeHummingbird the centralrectrix is sufficientfor species identification;plucking and preservingit can serveas documentation.The pandurateform of the centralrectrix will separateCalliope Hummingbirds from Rufous($elasphorus rufus), Allen's($. sasin),and Broad-tailed($. platycercus)hummingbirds and from membersof the genera Calypte, Archilochus, and Atthis. The Bumblebee(A. heloisa) and Wine-throated (A. ellioti) hummingbirdsof Mexicoresemble the Calliope,which occurs in the former'srange in migrationand winter,but their centralrectrices are smoothlytapered, not pandurate(Figure 1). CalliopeHummingbirds may be sexedon the basisof the centralrectrix oncethey havebeen aged. Aging is easilyaccomplished during summer and earlyfall by examiningthe billfor the presenceor absenceof corrugations. On winteringgrounds in Mexico,aging is more problematic,as knowledge of feather wear and molt sequencemust be considered. Wagner(1957) describedthe molt of CalliopeHummingbirds as occur- ringduring March and April. He reportedno datafor specieslike the Black- chinned(Archilochus alexandri), which nestsin the western and presumablyfollows a migratoryroute similarto the Calliope'sto winteringareas in Mexico.Most Black-chinsmolt betweenNovember and March(pers. obs.), so I suspectthat the Calliope'smolt is underwaybefore March.Determining the ageof femaleCalliope Hummingbirds may thus be difficultafter October if billcorrugations and bully feather fringes have been lost.

ACKNOWLEDGMENTS

I thankthe U.S. Fishand WildlifeService for continuedsupport of the manyon- goingresearch projects dealing with hummingbirdswith whichI am involved.Data suchas that presentedin the presentpaper would not be availablewithout the bandingand collectingprivileges extended to me. Variousstate wildlife agencies, 108 CALLIOPE HUMMINGBIRD PLUMAGES mostnotably the New MexicoDepartment of Gameand Fish,have also made this workpossible. For makingadditional comparative material available I thank the staff at the Denver Museumof NaturalHistory. Editorialsuggestions provided by Philip Unitt were very constructiveand much appreciated.

LITERATURE CITED

Baldwin,S. P., Oberholser,H. C., and Worley,L. G. 1931. Measurementsof birds. Sci. Publ. Cleveland Mus. Nat. Hist. 2. Baltosser,W. H. 1987. Age, species,and sexdetermination of four North American hummingbirds.N. Am. Bird Bander12:151-166. Banks, R. C. and Johnson, N. K. 1961. A review of North American hybrid hummingbirds.Condor 63:3-28. Coues,E. 1903. Key to North AmericanBirds, vol. 2, 5th ed. Dana Estesand Co., Boston. Elliot,D. G. 1881. A classificationand synopsisof the Trochilidae.Smithsonian Contr.Knowledge. 23:1-277. Johnsgard,P. A. 1983. The Hummingbirdsof .Smithsonian Inst. Press,, D.C. Ortiz-Crespo,F. I. 1972. A new methodto separateimmature and adulthumming- birds. Auk 89:851-857. Ridgway, R. 1892. The Humming Birds. Report of the United States National Museumfor 1890, pp. 253-383. Ridgway,R. 1911. The birdsof North and MiddleAmerica, part V. U.S. Natl. Mus. Bull. 50:300-681. SAS Institute.1988. SAS/STAT User'sGuide, version 6.03. SAS Inst., Cary, N.C. Stiles,F. G. 1971. On the fieldidentification of Californiahummingbirds. Calif. Birds 2:41-54. Stiles,F. G. 1972. Age and sex determinationin Rufousand Allen hummingbirds. Condor 74:25-32. Wagner,H. O. 1957. The moltingperiods of Mexicanhummingbirds. Auk 74:251- 257.

Accepted 14 January 1994

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