Ornithological Monographs 27

ECOLOGY LEK AND EVOLUTION MATING IN THE BEHAVIOR LONG-TAILED HERMIT HUMMINGBIRD BY F GARY STILES Escuela de Biologla, Universidad de Costa Rica, Ciudad Universitaria, Costa Rica AND LARRY L WOLF Departmentof Biology, SyracuseUniversity, Syracuse,New York 13210 ORNITHOLOGIC'•L MONOGRAPHS NO 27 PUBLISHED THE AMERICAN BY ORNITHOLOGISTS' WASHINGTON, 1979 D.C UNION OF ECOLOGY LEK IN AND MATING THE HERMIT EVOLUTION BEHAVIOR LONG-TAILED HUMMINGBIRD OF ORNITHOLOGICAL MONOGRAPHS This series,publishedby the AmericanOrnithologists' Union, has been establishedfor major paperstoo long for inclusionin the Union'sjournal, The Auk Publicationhas been made possiblethroughthe generosityof Mrs Carll Tucker and the Marcia Brady Tucker Foundation,Inc Correspondence concerningmanuscriptsfor publicationin the seriesshould be addressedto the Editor, Dr Mercedes S Foster, Department of Zoology, University of California, Berkeley, California 94720 Copies of OrnithologicalMonographsmay be ordered from the Assistantto the Treasurerof the AOU, Glen E Woolfenden,Department of Biology, University of South Florida, Tampa, Florida 33620 (See price list on back and inside back cover.) OrnithologicalMonographs,No 27, viii + 78 pp Editor of AOU Monographs,MercedesS Foster Editor of this number, John William Hardy SpecialAssociateEditors of this issue,MercedesS Foster, Department of Zoology,Universityof California,Berkeley,and Barbara K Snow, The Old Forge,Wingrave,Aylesbury,Bucks,England Authors,F Gary Stiles,Escuelade Biologia,Universidadde CostaRica, Ciudad Universitaria,Costa Rica, and Larry L Wolf, Department of Biology,SyracuseUniversity,Syracuse,New York 13210 First received, 15 January 1976; accepted,9 September1976; final revision completed, 15 March 1977 Issued September24, 1979 Price $8.50 prepaid ($7.50 to AOU members) Library of CongressCatalogueCard Number 79-67267 Printed by the Allen Press,Inc., Lawrence, Kansas 66044 Copyright @ by American Ornithologists' Union, 1979 ECOLOGY LEK AND EVOLUTION MATING IN THE OF BEHAVIOR LONG-TAILED HERMIT HUMMINGBIRD BY F GARY STILES Escuelade Biologla, Universidadde Costa Rica, Ciudad Universitaria, Costa Rica AND LARRY L WOLF Departmentof Biology, SyracuseUniversity, Syracuse,New York 13210 ORNITHOLOGICAL MONOGRAPHS PUBLISHED THE AMERICAN BY ORNITHOLOGISTS' WASHINGTON, 1979 NO D.C UNION 27 TABLE INTRODUCTION OF CONTENTS MORPHOLOGY AND GENERAL BIOLOGY OF PHAETHORNIS SUPER½ILIOSUS METHODS AND MATERIALS STVVY AREAS COLOR MARKING LEK 3 OBSERVATIONS FORAGING DATA AND NECTAR SAMPLING COLLECTING AND OTHER OBSERVATIONS LEKS, TERRITORIES, AND LEK BEHAVIOR SEX OF LEK RESIDENTS CHARACTERISTICS OF LEK SITES 7 SONG PERCHES AND TERRITORIES 10 VOCALIZATIONS 12 VISUAL DISPLAYS MATINGS, TRUE AND FALSE FORAGING PATTERNS FOOD PLANTS INTERSPECIES RELATIONS 15 18 21 21 25 STRATEGIES OF FLOWER EXPLOITATION 28 NECTAR 30 VS INSECTS TEMPORAL PATTERNING OF LEK ACTIVITY BREEDING AND LEKKING SEASONS DAILY PATTERN OF LEK ACTIVITY LEK DYNAMICS 32 32 35 43 SEASONAL VARIATION IN LEK COMPOSITION 43 SURVIVORSHIP AND RECRUITMENT 49 INTERMALE OF LEK RESIDENTS RELATIONS ON THE LEK INTER- AND INTRALEK MOVEMENTS DISCUSSION LEK EVOLUTION 56 58 SUPERCILIOSUS 58 COMPARISONS WITH OTHER HERMIT SPECIES 64 EVOLUTION OF LEK BEHAVIOR IN HUMMINGBIRDS 69 ACKNOWLEDGMENTS SUMMARY LITERATURE IN PHAETHORNIS 51 CITED 71 71 74 LIST Figure 11 FIGURES Map of La Selva property Monthly variation in temperature and rainfall at Finca La Selva History of spatial relations of three subleks in lek I from 1969 to 1972 Typical song perch Relation betweenterritory size and distanceof clear visibility from central song perches 11 Location of four songtypes on lek II in 1971 and 1972 14 Visual displaysof P superciliosusgiven around songperchesin lek territories 16 Number of speciesof food plants of P superciliosusin good bloom in different months, according to use categories 24 Daily nectar production of eight plant speciesfrequently visited by P superciliosus 10 OF 26 Cumulative use of food plants by P superciliosusin relation to corolla morphology and use by other hummingbirds 27 Records of distances at which individual male P superciliosus foraged from their territories 31 12 Estimates of the breeding seasonof P superciliosus 13 14 Annual variation in calling activity among residentmales on lek Ic 34 Daily variation in calling activity on leks II, Ia, and Ib for one day early and 15 Variation in daily calling activity of five males resident on lek Ic on 29 March, late in the 1970 lek season 1971 16 33 36 37 21 Variation in daily calling by male RY on lek Ic, end of 1971 lek seasonand beginning of 1972 season 38 Frequencyof chaseactivity on areasobservedduring all-day watchesat lek Ic 39 Seasonalvariation in daily calling activity from one territory on lek Ic 41 Presenceand territorial occupancyof male P superciliosuson lek I, February 1971 to April 1973 42 Locationsof lek Ia, "El Surfi," and lek Ic, "Surprise,"showingvegetationtypes, major landmarks, and distribution of major food plants 43 Locations of territories of males on leks Ia and Ic in March, May, June, July, 22 Locations 17 18 19 20 1971 23 24 25 26 of territories of males on leks Ia and Ic in December uary-March, 1972 Locationsof territories of maleson leks Ia and Ic in April, May, and August 1972 Locations of territories of males on leks Ia and Ic in January and March, 1973 Proportions of P superciliosusmarked at one site that were recorded at other sites different distancesaway Hypothesizedrelationshipof dominanceand/or fitnessto lek positionin leks of grouse and Ruff vs leks of P superciliosus vi 44 1971 and Jan- 46 47 48 56 62 LIST Table I OF TABLES Mensural characteristicsof Phaethornis superciliosus Numbers of territorial male Phaethornissuperciliosuson each of four leks during February-March in five seasons Observed temporal relationships of displays in 85 behavioral interactions in Phaethornis superciliosuslek territories 19 Morphology, period of good bloom, and hummingbird visitation of food plants of Phaethornis superciliosus 22 Feeding records of Phaethornis superciliosusat La Selva 23 Dominance relations of Phaethornis superciliosusat several food plants 28 Dominance relations of Phaethornis superciliosusand other hermits at different food plants 29 Observedflower visitsby lek males and other individualsalong a 450-m transect between lek I and the field station I0 I1 Daily activity patternsof Phaethornissuperci#osus in different habitats 32 Phaethornis superciliosusmist-netted at lek I, 1971-1973 40 Survivorshipof resident male Phaethornis superciliosuswithin and between lekking seasons: lek I, 1971-1972 12 13 52 Shifts in lek territories of resident male Phaethornis superciliosusin relation to previous status 15 50 Age structureof Phaethornissuperciliosuson lek I in 1971-1973 lekking seasons50 Subsequentstatus of young male Phaethornissuperciliosusfirst appearing on lek I in 1971 and 1972 14 32 53 Morphological and behavioral parametersof male Phaethornissuperciliosusin relation to lek position vii 55 INTRODUCTION In a lek matingsystem,severalmalesgatherin a localizedarea in the breeding season,where they display to other males and to females, the latter displays sometimes leadingto matings.Male courtshipassemblies occurin a variety of birds (e.g., Lack 1968), many frogsand toads (e.g., Emlen 1976), somemammals(Buechner1961;Leuthold1966;Bradbury,pers.comm.),and certaininsects (Wynne-Edwards 1962; Alexander 1975) In anurans and some insects, the concentrations of malescompetingfor matingprivilegesoccurwhere femalesare predictablylocalizedin spacedue to ovipositionrequirements.Although these aggregations may have a complexsocialstructure(Duellman 1967; Parker 1970; Campanellaand Wolf 1974; Emlen 1976), their evolutionaryhistory is distinct from that of certain birds and mammals,in which the male aggregations are generatedwithin the socialsystemitself The actual site of bird and mammal communaldisplaygrounds,or leks, is traditionalwithin the population Only a few of many potentialsitesare used over long periods In most of the species, at least the initial stagesof mating occur solely or principallyon the leks It generallyis assumedthat a numberof malesdisplayingtogetheris more attractive or stimulatingto femalesthan would be the sum of an equal number of males displayingseparately(Robel 1967); thus a male could potentiallyfather more offspringby joiningan assemblythan by displayingor waitingfor femalessolitarily In lek speciesan individual male, to maximize his chancesof mating, must be availablewhenevera receptivefemale arrives on the lek The evolutionof leks thusprobablyis limited to speciesin which malescan devotemost of their nonmaintenance time and energyto advertisingand defendingareasand courting femalesas they arrive This practicallyrequiresthe partial or total emancipation of the male from the reproductiveeffort beyondthe inseminationof the female (D Snow 1962, 1963) The strong selectivepressureon males for effective aggressive and courtshipcharacteristics, togetherwith the emancipationof the male from reproduction, have producedexaggerated sexualdimorphismin many lek species(Sibley 1957; Wynne-Edwards1962) Hummingbirdsand at least some speciesof grouse, shorebirds,manakins, cotingas,and birds-of-paradisemeet the prerequisitesfor the evolution of leks (D Snow 1963) Lek socialsystemsapparentlyare not uncommonin hummingbirds, but seemparticularlycharacteristicof the genusPhaethornis,the hermit hummingbirds.This is somewhatanomalousin that the speciesof this genusare rather dull colored,mostlywithoutmarkedsexualdimorphism.Publishedaccounts of Phaethornisdeal with general descriptionsof lek behavior (Nicholson 1931; Davis 1934, 1958; Skutch 1951, 1964a; Arp 1957; B Snow 1974) and song typeswithin and betweenleks (D Snow 1968; Wiley 1971) The patternof resourceexploitation of the populationrarelyhasbeenintegrated into any analysisof lek behavior (but see Kruijt et al 1972; Campanellaand Wolf 1974; Lill 1974, 1976; Pitelkaet al 1974) Hummingbirds are knownto be highlydependent uponnectarresources for breeding(reviewin Stiles1973), andcompetition for nectarin hummingbirds is welldocumented (e.g.,Cody1968; Wolf 1969, 1970; Stilesand Wolf 1970), yet thesefactorshave not been consideredin discussions of the evolutionof lek behaviorin hummingbirds In this ORNITHOLOGICAL TABLE MONOGRAPHS NO 27 MENSURAL CHARACTERISTICS OF PHAETHORNIS SUPERCILIOSUS Sample Sex N ,• SD Range 6` 6` 146 32 29 6.08 6.13 5.87 0.25 0.25 0.23 5.5-6.7 5.6-6.7 5.4-6.3 6' 146 37.49 1.18 34.0 40.0 6' 32 29 37.68 36.10 1.01 1.23 35.5-39.5 33.0-38.5 143 32 29 59.96 60.07 57.22 1.46 1.46 55.0-64.0 57.0-63.5 1.44 54.0-60.0 139 31 27 66.82 66.61 66.54 2.11 2.38 2.26 61.5-74.0 62.0-71.5 62.0-70.5 Weight (g) Known lek residents Collected birds x Bill length-•exposed culmen (mm) Known lek residents Collected birds Wing length flattened wing (ram) Known lek residents Collected birds Tail leng• -central rectrices (mm) Known lek residents Collected birds Sexed by dissection paperwe describein detailthe lek behaviorof the Long-tailedHermit (Phaethornis superciliosus)in Costa Rica and showhow its socialsystemis intimatelyrelated to patternsof flower exploitation;these are in turn stronglyaffectedby interspecificcompetitionfor nectar MORPHOLOGY AND GENERAL BIOLOGY OF PHAETHORNIS SUPERCILIOSUS Phaethornis superciliosus is a medium-sized hummingbird(6 - g) with a long, decurvedbill (37 mm) and generallydull-coloredplumage The underpartsare grayishbrown anteriorlyshadingto buff on the abdomen The dorsumvaries from dull bronzygreento dull purplishbronze,the feathersof the lower back and rump havingbroad buffy edgings.The face is conspicuously patternedwith a bully postocularstripe,a whitish-buffmalar stripe,and a buff stripedown the center of the throat; these contrast with the dark brown of the rest of the face and crown The maxilla is black, the mandible mostly dull pinkish orange The mouthlining is orange,and, togetherwith the facial stripes,producesa striking patternwhenthe bill is open The outer rectricesare grayishbrownbasally,and brownishblack medially,with narrow buffy tips The two central rectricesare greatlyelongatedand conspicuously white tipped Plumagesof the sexesare identical;however,most individualscan be sexed by measurements (Table 1) The plumageof immaturesdiffers from that of adults chiefly in having much more conspicuous buffy feather edgingson the back, crown, and tertials;no markedchangein plumagecolor occurswith age In addition,in the horny sheathof the maxilla immatureshave corrugations that graduallydisappearover a period of months(Ortiz-Crespo1972), making it possible to determine the approximate agein monthsfor manyyoungbirds (See Stilesand Wolf 1974 for detailsof the agingprocedure.) P superciliosus lacks 66 ORNITHOLOGICAL MONOGRAPHS NO 27 and Threneteshoverwith the longaxisof the bodyvertical,but in Gla'ucisand the smallerPhaethornis the bodyaxisis horizontal,andthe tail is raised the so-called "boat"posture(Skutch1951) A back-and-forth movement is mosttypical,but P longuemareus andP rubermayturn completecirclesin somesituations(Skutch 1951;Arp 1957;Davis1958) In general,the aerialdisplays of thesesmallspecies are considerably more elaboratethanthoseof the largerhermits,includingadditionalsoundeffects(Davis1958;B Snow1973a) Interestingly, percheddisplays suchas side-by-sidehave not been reportedin the small hermits The extension of the tongueplaysa role in the hoverdisplaysof P tuber (Davis 1958) andGlaucis(B Snow1973a) In a Guyanapopulationof P superciliosus, B Snow(1973b) observed that the bird visitinga territorialmaletypicallyperched besidehim andtouchedthe insideof his displayed gapewith its tongue.We never observedthis in the Costa Rican populationof P superciliosus, althoughthe displayotherwiseseemssimilar to a side-by-side.Guyananpopulationsof P superciliosus alsohave a specialflight call usedonly on the lek; we never heard sucha call in CostaRica It is worth notingthat the conspecificity of the Central and SouthAmericanbirdsis in question(Meyer de Schauensee 1966) Tock or pop soundsare producedby P guy, P supercilious,and rarely, by Glaucishirsuta(B Snow 1973a) The associated gapedisplayis more elaborate and spectacularin P guy than in P superciliosus, involvinga more conspicuous spreadingof the mandibularrami; the gape is bright red in P guy The tock displayof P guy has both side-to-sideand dartingmovements;the rock or pop is given at the endsof rapid sidewaysarcs In additionto usingthe rock in all of the samesituationsas P superciliosus use the bill-pop, male guy also characteristicallytock-displaywhen changingperchesin their territories,or may hover and tock-displayrepeatedlyover a perch Tock or bill-pop soundsmay be produced by a suddenexpulsionof air from the glottisin conjunctionwith a snappingopen of the bill B Snow (1974) describedseveral casesof loss of voice in P guy and suggested that the tock is producedvocally in that speciesbecauseon losingits voice, a bird no longercould tock Becauseair comingfrom the lungsor air sacs must passthroughthe syrinx en route to the glottis, the two explanationsare not mutually exclusive Perch exchangesequencesare known for P superciliosus, P guy (B Snow 1974), P longuemareus(D Snow 1968), and Threnetes leucurus (B Snow 1973a); they probablyoccurin mosthermitsas they seemto be a ritualizedform of precopulatorymountingthat occursregardlessof the sex of the sittingbird Copulationin most or all speciesresemblesthat in P superciliosus(Fig 7H); Davis' (1958) reportof aerial copulationin P tuber has not been confirmedby other authors (B Snow 1973a) Severalauthorsattemptto discriminatebetweendisplaysgivento femalesand thosegivento othermalesby lek residents.In the sexuallydichromaticspecies (P ruber, P guy) this may be feasible,but it is complicatedby the fact that in at least the latter, young malesare indistinguishable from femalesby plumage and approachthe lek like females(B Snow1974) Many of the supposed female visitsto the lek endingin chasesmay have been by yearlingmalesthat had not yet obtaineda lek territory In view of the variabilityin displaysequences found in P superciliosus (Table 3), thereis no satisfactory evidencethat the displays LONG-TAILED HERMIT HUMMINGBIRDS 67 of a lek residentto a visitingmaleor femaleare qualitatively different,andevidence for even a quantitativedifferenceis weak (B Snow 1974) The similarity may includeeven mountingand attemptedcopulationif a perchingmale sits still Homosexualmountingand similarityof mating and male aggressive displaysin P superciliosusare consistentwith the limited information for other hummingbirds,includingnonlekspecies(Stilesand Wolf 1970; Stiles1973; Wolf 1975a; Stilesand Ortiz-CrespoMS) The brief, rare, and unpredictableappearances of femaleson male territories (B Snow1974; this study)are probablymajorfactorsin the frequencyof leaf copulations or falsematingsin mosthermitsand manyotherhummingbirds.Such behaviorhasbeenreportedfor variousspecies of Phaethornis (Arp 1957;D Snow 1968;B Snow1973a, 1974; presentstudy),Threnetes(B Snow1973a), Glaucis (B Snow1973b), andhasbeenseenin Eutoxeres(Stiles,pers.obs.) The analogy to masturbation in mammals is obvious The only other study of lek behavior in hummingbirdsthat deals with such parametersas survival,recruitment,molt, and foragingof lek residentsis the work of B Snow(1974) on Phaethornis guyin Trinidad P guy is a fairly closerelative of P superciliosus but showsmarked sexualdimorphism,and young males pass through several more or less intergradingplumagestagesbefore acquiringthe definitive plumage B Snow did not work with marked birds, but stated that "differencesin head markings,combinedwith differencesin calls (songs), made it possibleto identifya numberof individualswith a high degreeof certainty." Her interpretationof plumagesequences, whichis crucialto her evaluationsof survivorship and recruitment,is basedlargelyon territorialoccupancyby birds of similar songtype in differentyears In P superciliosus, at least, it may not be safeto assumethat a bird singingfrom the sameterritory with the samesong asthe previous years'residentis in factthe sameindividual.We havemanycases of individualturnoverin whichthe songtype of the territoryholder remainsthe same(seeFig 6, esp.BRG and WPB) Therefore,certainof Snow'sconclusions requireconfirmation from studieswith markedbirds In general,temporalandspatialpatternsof lek activityin P guyresemble those of P superciliosus Territory sizein P guy averagedslightlylarger, but from B Snow'scommentsregardingfrequentvisualcontactof singingmaleswe infer that the vegetation on the guy leks wassomewhatmore openthan that on our superciliosusleks The lekking seasonof guy began in November,but less suddenly than that of superciliosus; only by mid-Decemberwere all males attendingthe lek regularly Highestdisplayintensities in guy (numberof tocksper minute)wereattained at the startof the lekkingseasonand declinedslightlythereafter,as in superciliosus Thedailypatterns of lek activityof individual maleguyfell intolatemorning and afternoonperiodsas in superciliosus, but no data are availablefor guy before 0630, so an early morningactivity period is conjectural.Most adult male guy regularlyattendedthe lek from late DecemberthroughMay or June P guy and superciliosus differedgreatlyin the timingof the annualmolt In guy the molting seasonfollowedthe lekkingseasonwith little or no overlap;adult malesleft the lek for the year as they startedto molt The slow molt and possiblyuniquetiming mechanismof superciliosus (Stilesand Wolf 1974) resultin extensivemolt-breeding 68 ORNITHOLOGICAL MONOGRAPHS NO 27 overlapand correlatewith a somewhatlongerlekking seasonthan in guy (8-9 versus6' months) Most youngguy malesfirst appearedon the lek in April or May and moved into centralterritoriesas the adultsleft; their behaviorcloselyresembledthat of young male superciliosus.At this time they were in fresh plumage,and Snow concludedthat they had just completeda molt and must, therefore,be in their secondseason.From our experiencewith superciliosus, includingagingof young malesby bill corrugations, we think it more probablethat the fresh plumageof youngmale guywas the first-yearplumage,and that thesemaleswere only a few monthsold B Snowstatedthat theseyoungmaleswent througha secondseason in this sameplumage.If our interpretationof their agesis correct,theseyoung male guywore their juvenalplumagefor 15-18 monthsand moltedannuallythereafter Preciselysucha molt schedulehas been documentedin P idaliae (Ruschi 1967) In P superciliosus the juvenal plumagealso is worn for slightlylonger than any succeeding feather coat (Stiles and Wolf 1974) B Snow (1974) distinguished threeother plumagesof youngmales,whichshe interpretedas differentyear classes.Theseclassesappearto us to intergradeand may even representonly a single,variable second-yearplumage Thus the adult male plumagein P guy is attained somewherebetweenthe secondand fourth completeannual molt; this is the most elaborateplumagesequenceyet known for the genusPhaethornis Accordingto B Snow,annualturnoverof lek malesin P guy was 10% or less, a far lower figure than we found for P superciliosus.Part of this differencecould reflect inherentbiasesin our respectivemethods The use of territory location and song type to identify individualscertainly is unsafe in P superciliosusand might well underestimateturnover in P guy On the other hand, our marking systemcouldhave reducedsurvivorshipin P superciliosus.However, most mortality occurredwhenwe handledthe birdsleast,and we excludedfrom the analysis all individualsthat we felt mighthavebeenadverselyaffectedby the tags Conceivably,the tag couldweakena bird just enoughto affect its survivorship over the lean season,but such effectswere probablyvery minor at best Each tag weighedless than 0.1 g, far lessthan a crop of P superciliosuswhen filled with nectar (Hainsworthand Wolf 1972b), and the plasticwas too stiff and short to become tangled easily invegetation Thetagsmayinterfere withnesting byfemales (Waser and Calder 1975), but our data on survivorshiptreat only lek males Even allowingfor thesepossibleerrors of estimation,we feel that a real demographicdifferenceexistsbetweenP guy on Trinidad and P superciliosus at La Selva, reflectingdifferingrates of both reproductionand mortality The longer breedingseasonof P superciliosus makespossible morenestingattempts.Indeed, there is time for up to three successful nestingsin the breedingseasonof P superciliosus,two in the breedingseasonof P guy Thus the annualreproductiveoutput of the former could be as much as 50% greater than the latter, althoughthe differenceprobablyis less due to the low nestingsuccessin both populations Regarding mortality,at leastoneimportantpredatoron adulthummingbirds (Stiles 1978b), the Tiny Hawk (Accipitersuperciliosus), is absentfrom Trinidad (ffrench 1973) However, most other potential predators, including snakes, are well representedon Trinidad (D Snow and B Snow 1964) More important than LONG-TAILED HERMIT HUMMINGBIRDS 69 differencesin predationbetweenthe two areasmay be differencesin the seasonal distributionof nectar resources.In Costa Rica the seasonof low nectar availability from late Octoberto early Decemberwas very severe,with no abundantfood plant availableover mostof La Selva The relativelyshorthiatusbetweenthe blooming seasonof the two major food plants of P guy on Trinidad was bridgedby the bloomingof a third species(B Snow1974) To judgefrom the numberof feeding recordsfor the latter, it wasfairly abundant(B Snowand D Snow 1972) Without the high mortality during October and November, annual survivorshipin superciliosusat La Selvawould approachthat claimedby B Snow for P guy on Trinidad If one acceptsB Snow'sestimatesof turnover in P guy and considersthe differencein reproductiveoutput of the two populationsto be 50% or less,then there mustbe a relativelygreatersurplusof youngmalesproducedeachyear in P guy that not obtainlek territories A possibleindicationof this is the high frequencyof "female" visitsto P guy leks Snow did not considerthe fate of suchmales,or of the demographicconsequences of sucha low recruitmentrate The presenceof numerousnonbreedingmales may limit reproductionof the populationby depletingnectarsuppliesthat otherwisecouldbe availableto females It would be most useful to know the interval between successive clutches in females of the two populations,but suchdata are virtually impossibleto obtain in such a dense habitat EVOLUTION OF LEK BEHAVIOR IN HUMMINGBIRDS TWOconditionsseemnecessary for the evolutionof lek behaviorin any organism: (1) the emancipationof the male from participationin the reproductiveeffort beyondinsemination and (2) sufficienttimebeyondthat requiredfor maintenance to controla lek territory (D Snow 1962, 1963) A variety of animal species, includingvertebratesand invertebrates, meet the first condition.For birds and mammals,Orians (1969) suggested ecologicand demographic situationsin which to expectmale emancipation.Amonghummingbirds, almostall speciesmeet the prerequisites for the evolutionof lek behavior,apparentlyrelatedto the fact that the clutchis two eggsthroughoutthe family (Van Tyne and Berger 1959; Orians 1969) However, severalinstancesof apparentlysecondaryreestablishment of male aid in reproduction have been discovered recently(Wolf and Stiles 1970; B Snow 1973a) Male aid, howeverindirect,is probablyincompatiblewith the time and energydemandsof a lek socialsystem.One thereforeshouldnot expect leks to occurin speciesin whichthe femalescan producemore offspringwith aid from the male than without it (cf Orians 1969) Once emancipatedfrom the reproductiveeffort, male hummingbirdsare under selectionchieflyto increasematingfrequencyand reducemaintenancecosts Males of manyspeciescombinefeedingand matingby holdingflower-centered territories duringthebreedingseason.Generally,malehummingbirds are dominantto females and controlthe bestfeedingareas,sofemalesattemptto forageon male territories Most matingsare initiatedon theseterritoriesas a resultof foragingby females (Wolf and Stiles 1970; Stiles 1973; Wolf 1975a) The number of flowers a male can control on such a territory affectsnot only his energybudgetbut probably 70 ORNITHOLOGICAL MONOGRAPHS NO 27 his mating successas well; the flowers in effect constitutea secondarysexual character (Wolf and Stiles 1970; Stiles 1973) Thesematingand feedingterritoriesand lek territories,representing complete coincidence and completeseparationof defendedmatingsitesand feedingareas, obviouslyare but the ends of a continuum Within a single speciessome males controlenoughflowerson territoryto satisfyall of their energyrequirements,and othersthat hold fewer flowers are requiredto forage outsideof their territories for varyingperiods(Stiles 1971a, 1973) In fact, in Calypte anna of California, changesin the dispersionof flowers can producelocal social systemsthat run the entiregamutfrom food-centered matingterritoriesto essentially leks In the latter case,males hold flowerlessterritoriesin chaparralvegetationand commute to Eucalyptustrees to feed (Stiles 1973) In view of time and energy,the optimumstrategyfor a male wouldbe to hold a food-centeredmating territory rich enoughto supporthim for a day This would enablehim to forageefficientlyand to be presentcontinuously so as not to missvisitsby females Whether a male can hold such a territory dependson the abundanceand dispersionof suitable flowers, the number of competing hummingbirds,the male's dominancestatus among his conspecifics,and the positionof his speciesin the interspecificdominancehierarchy(Stiles and Wolf 1970) When it is consistentlyimpossiblefor males of a given speciesto hold such rich breeding-feeding territories,selectionmay favor the evolutionof lek matingsystems.Certainadvantages of flower-centered territorieswith regardto the criteria availableto femalesfor male choice are also offered by lek systems, andthesemay not be offeredby otheralternativestrategies, suchas malesdisplay- ing solitarily.Theseincludethe fixed,constantlocationsof male matingstations and an indexof male'sdominancestatusindependentof his personalcharacteristics -•his positionin an activity gradient Lek social systemsand food-centered territoriesshouldthus representadaptivepeaks,and one may expectthat more hummingbirdspeciesof a given area showthesetypesof matingsystemsthan other,intermediatetypes At La Selvaat least,this predictionis upheld At least species (Chalyburaurochrysia andprobably Amaziliatzacatl)showfood-centered matingterritories, while6 (Eutoxeres aquila,Phaethornis superciliosus andlonguemareus,Threnetesruckeri,Klaisguimeti,and,,Imaziliaamabilis)form leks Glaucis aeneamayholdindividualterritories(cf B Snow1973a) The matingsystems of the other commonresidentspecies,Florisugamellivoraand Thaluraniafurcata, are unknown The criticaldeterminantof the adaptivepeak toward which a species mayevolveappears to be whetherbreedingmalescancontrolrich feedingareas which then serve as mating stations To understandthe evolution of lek behavior it is thus important to identify factorsthat may preventmales of a given speciesfrom holdingfood-centered matingterritories.Lek-formingCostaRican hummingbirds include(1) subordinatespecies in the community that are forcedfrom defensible food supplies by dominantspeciesand (2) speciesthat havespecialized on a food supplywhose spatialand/ortemporaldistributions makeit nondefensible (Brown 1964; Gill and Wolf 1975; Wolf et al 1975) Included in the latter category are very large, dominantspecies that useresources defendedby subordinate speciesbut for which sufficientlylarge concentrations of flowersto justify territorialityseldomor never LONG-TAILED HERMIT HUMMINGBIRDS 71 occur Speciesin this categoryincludePhaeochroa cuvierii(Skutch1964b;Wolf 1970, pers obs.), Campylopterus hemileucurus (pers obs.) and, in Guyana, Topaza pella (Davis 1958) The lek-forming hermits,as a group,fit intothe category of subordinate species (Stiles 1975, presentstudy) The two nonhermitsat La Selva that form leks, Klais guimeti and Amazilia amabilis, are small, subordinatespeciesthat are excludedfrom mostrich nectarsources(pers obs.) Suchspeciesare forcedto exploita wide rangeof food plants,manyof whichgrowin nondefensible spatial arrangements or haveinsect-pollinated flowersthat produceverylittle nectar(Wolf 1970; B Snowand D Snow 1972; Hainsworthand Wolf 1972a; Wolf et al 1976) It is importantto note that the two categoriesaboveare not exclusiveand that subordinate statuswith exclusionfrom rich nectarsourcesand specialization for feedingat nondefensible food plantscan evolveconcurrently.This clearlyhas occurredto a high degreein the hermits,includingP superciliosus, and has led to the coevolutionof hermitsas route-foraging, nonterritorialpollinators,and a groupof flowersecologically andmorphologically specialized for hermitpollination (B SnowandD Snow1972; Wolf et al 1972; Linhart 1973; Stiles1975) Clearly the exploitationsystemsof hummingbirdsare intimately related to their social systems; the two are tightlyintegratedin the ecologyof any hummingbirdspecies We contendthat the evolutionof leks in P superciliosus and other hummingbirds cannotbe adequatelyunderstoodwithout detailedconsideration of selectiveforces arisingfrom the foragingstrategy,interspecies relations,molt, and resourcedistribution in time and space ACKNOWLEDGMENTS This studywas supportedby a Chapman-Naumberg Postdoctoral Fellowship from the American Museum of Natural History to Stiles, and National Science FoundationgrantsGB-7611, 19200, 40108, and 28956X to Wolf We are grateful to the CostaRican officeof the Organizationfor Tropical Studies(O.T.S.) especially J Campabadal,for logisticalsupportat La Selva Help in the field was providedby P Campanella,F R Hainsworth,L Hurd, L F Kiff, D Lyon, S M Smith, and the participantsof severalO.T.S courses.Weather data for La Selvawere providedby R Chavardaand G Hartshorn Helpful discussions and commentson the manuscriptwere suppliedby J Bradbury,P J Campanella, D H Janzen,P Marler, G H Orians,S M Smith,D and B Snow,R H Wiley, and D Windsor To all of thesepeopleand institutionswe expressour sincere thanks SUMMARY The ecologyand lek matingbehaviorof the Long-tailedHermit, Phaethornis superciliosus, were studiedover a four-yearperiod at Finca La Selva, in the wet Caribbeanlowlandsof Co.staRica The sexesof this hummingbirdare alike in plumagebut differ in measurements; all lek residentsare males Most of our observations were made on color-marked birds Densityof P superciliosus leks at La Selvawasaboutone per km2 Four leks had 5-6 to 20-25 malesduringthe studyperiod In undisturbed forest,lekswere 72 ORNITHOLOGICAL MONOGRAPHS NO 27 located in dense thicketsalong streams,which provided convenientflyways as well as habitat for importantfood plants Lek territorieswere mating stations only,nevercontaining enoughflowersto affectthe male'senergybudget.A territory consistedof a male'ssongperchesand the area betweenthem The foci of lek activitywere the songperches.Territory sizevaried directlywith the opennessof the vegetation Songwas the major meansof territorial advertisement; maleson territory were rarelyin visualcontactand spentmostof their time singing.Distinctsongtypes or dialectsoccurredin P superciliosus; malessinginga given dialectgenerally occupieda geographical subunitof the lek, and the numberof subunitsvaried directlywith lek size In spiteof turnoverof individualmales,thesesubunits tendedto retaintheir integrityfrom year to year; maleson particularterritories sangthe samedialectsas their predecessors Visual displayswere givenonly whentwo birdswere in closecontact,usually at a songperch The conspicuous facial stripes,orangemouth-lining and lower mandible,andperhapsthelong,white-tipped tail werethe mostimportantmorphological structuresusedin visualdisplays,someof which were associated with distinctivesounds.Allowing for differencesin colorationof head and bill, the displays of P superciliosus are fairly similarto thoseof otherhermits.No regular sequence of displayswas evidentin all interactions, but certaindisplaystended to precedeor follow otherswith someconsistency The displaysand aggressiveness of an intrudingmale peakedwhen he first invadedanother'sterritory Duringthe ensuingexchange of displays,the resident becameprogressively moreactive,in mostcasesfinallydrivingthe intruderfrom the territory We found no differences in displaysgiven to male and female intruders,and observedhomosexual aswell as heterosexual copulations.A female apparently signaled her sexby simplysittingstillandallowingthe maleto mount; a male treatedanythingthat sat still as a willingfemale Mating sequences were alwaysinitiatedin the males'territories,althoughcopulationmighttake place elsewhere Lek malesforagedmostlywithin 200-500 m of the lek, dependingon the distributionof suitableflowers The remainingareas were used mainly by non- residents, mostlyfemales;all nestswerefoundwell awayfrom established leks P superciliosus foragedmainlyat flowerswith long,curvedcorollasthat were usedinfrequently by nonhermithummingbirds that were dominantto hermits andusuallydisplaced themat flowers.IndividualP superciliosus visiteda series of small,nondefensible clumpsof flowers,apparentlyalong a regularforaging route The mostimportantfoodplantsof P superciliosus at La Selvawereseveral species of Heliconia, especially H pogonantha, andCostus The lekkingseasonof P superciliosus commenced abruptlyin late November or December,mostmalesreturningto thelek withina few weeks.Onsetof lekking wasclosely correlated withtheonsetof goodbloomby H pogonantha Lek activity peaked by January, andhighlevelsweremaintained through Juneor July The nesting andlekkingseasons corresponded closely, but nesting did not peakuntil Februaryor March, as otherdry-season flowersbeganto bloomprofusely.A sharpdropin lekkingand nestingoccurredin Augustwhile flowerswere still abundant,perhapsreflectingselectionagainstlate nestings.Flower availability LONG-TAILED HERMIT HUMMINGBIRDS 73 declinedprecipitously afterlate August,and the annualminimumof lekkingand nestingcorresponded with a periodof extremescarcityof flowersin Octoberand November Duringmostof the breedingseason,daily peaksof lek activityoccurredin early morning,late morning,and midafternoon.Males arrivedon the lek at dawnbefore feeding,and sangand interactedvigorously for 30-45 An hour of concentrated, synchronous foragingfollowed The late morningincludedintensesinging and lessovert aggressive activity, and in the afternoonmalesdid little more than sing This declinein activeterritorialaggression throughthe day paralleledthe declinein nectarsecretionof major food plants,and the early morningforaging periodcorresponded to the time of maximumnectaravailability Most of the rare, brief visits to the lek by femalesoccurredduring the late morningactivityperiod,when all observedcopulationsalso occurred We estimate that only about one female per day visiteda lek of 15 malesfor the purposeof mating,probablya resultof the long,asynchronous breedingseason.Males therefore had to be ready for monthsto mate at an instant'snotice, yet the number of matingsper male was relativelylow This may explain the males' willingnessto mate with anythingcompliantand their frequent copulationswith dead leaves Young maleshatchedearly in the breedingseasonbegan to appear on the leks in March, but did not becomenumerousuntil May or June At first theseyoung malessanghesitantly,with no fixed dialectand from any positionon the lek, and they were frequentlydisplacedby the residents.A few young.malesestablished peripheralterritoriesby May or June, but most did not becometerritorial until July when adultsbegan leaving the lek for the year Residentswere dominant until they departed By Augustmost territorial,singingmaleson the lek were youngof theyear No singlefactorcouldaccountfor the departureof the residents; molt played a role in somebirds but not in others The decline of flowers on a bird's foragingroute may also have been important;birds that had to find new feeding areas may have had lesstime to spendon the lek The annualturnoverof lek residentsin the La Selvapopulationof P superciliosus wasabout50%, far higherthanreportsfor otherneotropicalbirds,includingP guy in Trinidad About 75% of the annual mortality occurred during October and Novemberwhen flowerswere scarce Survivorshipof adult and first-year males was similar, perhapsreflectingthe pronouncedyear-to-yearvariationsin flower availabilitythat decreasethe valueof previousforagingexperienceto adults Nearly all recruitmentof new residentswas from the ranks of yearlingmales The more experiencein territorialbehaviora youngmale had duringhis first season,the betterhischancesof becominga residentthe followingyear Youngmaleshatched late in the seasonand with little previouslek experiencealso had a chanceto becomelek residentsdue to the high mortality of older yearlingsor adults The mostdominantresidentson a P superciliosus lek occupiedterritoriesnear the center,with subordinateindividualstowardsthe periphery Central territories were the moststablein time and spaceand the moststronglycontested.Residents of the previousyear returningto the lek nearly always reoccupiedtheir old territoriesor vacantterritoriesmore toward the centerof the lek Young males returningat the start of their first full lekkingseasonwere able muchlessoften to reoccupy the siteson whichtheywereterritorialor interactedas yearlings but 74 ORNITHOLOGICAL MONOGRAPHS NO 27 usuallyhad to settle in more peripheralsites Most movementtowardsthe lek centeroccurredduringthe lekkingseasonas centralresidentsdied However,the dominancestatusof someindividualschangedlittle with age, even over several years We foundno morphological characterthat was consistently correlatedwith dominance,althoughsmall, short-billedmalesoften failed to obtain territories Becausethey were often in denservegetationwith defendedboundarieson all sides,central territoriestendedto be smallerand closertogetherthan peripheral territories.Centralmalessangmorethanperipheralmalesduringthe late morning when femaleswere likely to appear,in part becauseperipheralmaleswere persecutedmore by centralmales Thesefactorsproduceda gradientin activity and overallsongvolumeper unit areafrom the lek centertowardsthe periphery.Male P superciliosus tried to hold territorieswhere activitylevels were high If, as seemslikely,femalespreferto matewith the mostdominantmales,thentheir most reliablecue to a male'sstatusmay be his positionin the lek activitygradient In general,the dominance/fitness gradienton P superciliosus leks appearsto be muchlesssteepthan that on leks of certaintetraonidsand shorebirds.The proportionof all matingsaccountedfor by centralmalesis probablyless, and subordinatemales have some chance of mating Unless other factors intervene, anymatingadvantage at the centershouldsetup geneticfeedbackdrivinga hermittypelek towardmorestructured, grouse-type conditions.In P superciliosus these factorsincludethe high annualturnoverof residentsand the generalrarity and unpredictabilityof mating Nearlyall hummingbirds satisfythe basicprerequisites for the evolutionof leks: emancipationof the male from the nestingeffort and a highly predictablefood source(flowers) The mostenergetically efficientmatingstrategyprobablyis to controla rich flower supplyon the matingterritory Leks tend to evolvein hummingbirds whenthisis impossible, eitherbecausedefensible flowersare controlled by more dominantspecies,or becausesufficientlyrich, defensiblenectarsources not occurin the species'habitat As a group,the hermits,includingP superciliosus,fall into the first category.They have concurrentlyevolveda high degree of specialization for exploitingnondefensible flowers,and manysuchflowershave coevolvedmorphological and ecologicalspecializations promotinghermit pollination Leks and flower-centeredmating territoriesrepresentthe ends of a continuumof matingtypesin hummingbirds At La Selvamostspeciesshowone extremematingsystemor the other;relativelyfew speciesare intermediate.The two extremestrategiesmay well representadaptivepeaks LITERATURE CITED ALEXANtmR,R.D 1975 Natural selection and specialized chorusing behavior in acoustical insects In: Pimentel, D (ed.) Insects, Science, and Society Academic Press, New York Pp 35-77 ARe, W 1957 Observacionessobre el comportamiento en grupo del Phaethornis longuemareus (Aves-Trochilidae) Bol Soc Venezolana Hist Nat 17: 156-168 BROWN, J L 1964 The evolution of diversity in avian territorial systems Wilson Bull 76: 160-169 BUECH•ER,H.K 1961 Territorial behavior in Uganda kob Science 133: 698-699 , AND H D ROTH 1974 The lek system in Uganda kob antelope Amer Zool 14: 145-162 LONG-TAILED HERMIT HUMMINGBIRDS 75 CAMPANELLA, P J., ANDL L WOLF 1974 Temporalleksas a matingsystemin a temperate zone dragonfly (Odonata: Anisoptera) I Plathemislydia (Drury) Behaviour51: 49-87 Co)ắ,M L 1968 Interspecificterritoriality among hummingbirdspecies.Condor 70: 270-271 DANIELS,G S., ANDF G STILES 1979 The Heliconia taxa of Costa Rica: keys and descriptions.Brenesia15, suppl.1: 1-150 DAVIS, T A W 1934 Notes on display in the hummingbirdsPhaethornis superciliosus (Linn.) and Pygmornis ruber (Linn.) 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Ardea 54: 109-229 HOLDRIDGE, L R., W C GRENKE,W H HATHEWAY, T LIANG,ANDJ A TOSI, JR 1971 Forestenvironments in tropicallife zones: A pilot study New York, PergamonPress JANZEN, D.H 1971 Euglossine beesas long-distance pollinatorsof tropicalplants Science 171: 203-205 JEHL,J R., JR 1970 Sexualselectionfor size differencesin two speciesof sandpipers Evolution 24: 311-319 KRUIJT,J.P., ANDJ A HOGAN 1967 Social behavioron the lek in the black grouse, Lyrurus tetrix tetrix (L.) Ardea 55: 203-240 , C J DEVOs,ANDI BOSSEMA.1972 The arenasystemof Black Grouse,Lyrurus tetrix tetrix (L.) LACIC, D Proc 15th Intern Ornithol Congr.: 399-423 1968 Ecologicaladaptations for breedingin birds London,Methuenand Co., Ltd LEUTHOLD, W 1966 Variationin territorialbehaviorof Ugandakob ,4denotakob thomasi (Neumann 1869) Behaviour 27: 214-257 LILL, A 1966 Someobservations on socialorganizationand nonrandommatingin captive Burmesered junglefowl (Gallus gallusspadiceus).Behaviour26: 228-242 1974 Sexualbehaviorof the lek-formingWhite-beardedManakin (Manacusmanacus trinitatis Hartert) Z Tierpsychol.36: 1-36 1976 Lek behaviorin the golden-headed manakin,Pipra erythrocephala in Trinidad (West Indies) Adv in Ethology,Suppl 18 to J Comp Ethology LINHtmT,Y.B 1973 Ecologicaland behavioraldeterminants of pollen dispersalin hum- mingbird-pollinatedHeliconia Amer Naturalist 107: 511-523 MEYE• •)E SCHAOE•qS•, R 1966 The speciesof birds of South America and their distributions Narberth,Pennsylvania, LivingstonPress NICHOLSON, E.M 1931 Communaldisplayin hummingbirds.Ibis 1: 73-83 76 ORNITHOLOGICAL MONOGRAPHS NO 27 ONIKI, Y 1970 Nesting behavior of reddish hermits (Phaethornis ruber) and occurrenceof wasp cells in nests Auk 87: 720-728 ORGANS, G.H 1969 On the evolution of mating systemsin birds and mammals Amer Naturalist 105: 589-603 ORT•Z-CRESPO, F I 1972 A new method to separate adult and immature hummingbirds Auk 89: 851-857 PARKER,G.A 1970 The reproductivebehavior and the nature of sexual selectionin Scatophaga stercoraria L (Diptera: Scatophagidae) I and II J Anim Ecol 39: 185-228 PrrELr•, F.A 1942 Territoriality and related problemsin North American hummingbirds Condor 44: 189-204 , R T HOLMES, AND S F MACLEAN,JR 1974 Ecology and evolution of social organizationin Arctic sandpipers.Amer Zool 14: 185-204 ROBEL,R.J 1966 Booming territory size and mating successof the Greater Prairie Chicken (Tympanuchuscupidopinnatus) Anim Behav 14: 328-331 1967 Significance of booming grounds of Greater Prairie Chickens Proc Amer Phil Soc 111: 109-114 RUSCHI, A 1950 O territ6rio e as ftreas de alimenta•fio e de nidifica•fio de Anisopterus pretrei (DeLattre and Lesson), observadasatrav•s algumasgera•6es Bol Mus Biol Prof Mello-Leitfio 8: 1-20 1961 Algumas observacoessobre: Phaethornis yaruqui yaruqui (Bourcier); etc Bol Mus Biol Prof Mello-Leitfio 27: 1-21 1967 A plumagem e a muda em Phaethornis idaliae Bol Mus Biol Prof MelloLeitfio 33: 1-5 SCHoENER, T.W 1971 Theory of feedingstrategies.Ann Rev Ecol Syst 2: 369-404 SIm.EY, C.G 1957 The evolution and taxonomic significanceof sexual dimorphism and hybridization in birds Condor 59: 166-191 SKUTCH,A.F 1951 Life history of Longuemare'sHermit Hummingbird Ibis 93: 180-195 1958 Life history of the Violet-headedHummingbird Wilson Bull 70: 5-19 1964a Life histories of hermit hummingbirds Auk 81: 5-25 1964b Life history of the Scaly-breastedHummingbird Condor 66: 186-198 1966 A breedingbird censusand nestingsuccessin Central America Ibis 108: 1-16 Life histories of Central American highland birds Publ Nuttall Ornithol 1967 Club Si•UD, P No The birds of Finca "La Selva," a tropical wet forest locality Bull Amer 1960 Mus Nat Hist 121: 49-148 1964 The birds of Costa Rica: distribution and ecology Bull Amer Mus Nat Hist 128: SMITrI, S M 1-430 1976 A field study of dominancehierarchiesin Black-cappedChickadees Auk 93: 95-107 SNow, B.K 1972 A field studyof the calfbirdPerissocephalus tricolor Ibis 114: 139-162 1973a Socialorganizationof the hairy hermit Glaucishirsuta Ardea 61: 94-105 1973b The behavior and ecologyof hermit hummingbirdsin the Kanaku Mountains, Guyana Wilson Bull 85: 163-177 1974 Lek behaviourand breedingof Guy's Hermit Hummingbird Phaethornisguy Ibis 116: 278-297 , ANDD W SNow 1972 Feedingnichesof hummingbirdsin a Trinidad valley J Anim Ecol 41: 471-485 SNow, D.W 1962 A field studyof the Black and White Manakin, Manacusrnanacus,in Trinidad Zoologica 47: 65-104 1963 The evolution of manakin displays Proc 13th Intern Ornithol Congr.: 553-561 1968 The singingassemblies of little hermits Living Bird 7: 47-55 , ANDB K SNOW 1964 Breedingseasons and annualcyclesof Trinidadland-birds Zoologica 49: 1-39 LONG-TAILED HERMIT , •,NI>-Ardea HUMMINGBIRDS 77 1973 The breeding of the Hairy Hermit Glaucis hirsuta in Trinidad 61: STILES,F.G 106-122 1971a Time, energy, and territoriality of the Anna Hummingbird (Calypte anna) Science 171: 818-821 1971b On the field identification of California hummingbirds California Birds 2: 41-54 1973 Food supply and the annual cycle of the Anna Hummingbird Univ Cali- fornia Publ Zool 97: 1-109 1975 Ecology, flowering phenology,and hummingbird pollination of some Costa Rican Heliconia species.Ecology 56: 285-302 1978a Temporal organizationof flowering among the hummingbirdfood plants of a tropical wet forest Biotropica 10: 194-210 1978b Possible specialization for hummingbird-hunting in the Tiny Hawk Auk 95: 550-553 , AND L L WOLF Auk 1970 Hummingbird territoriality at a tropical flowering tree 87: 467-491 , AND- 1973 Techniques for color-marking hummingbirds Condor 75: 244- 245 , riND 1974 A possiblecircannual molt rhythm in a tropical hummingbird Amer Naturalist VnN RmJN, J 47: 1973 108: 341-354 Behavioral dimorphism in male Ruffs, Philornachuspugnax Behaviour 153-229 VAN TYNE, J., AND A J BERGER 1959 Fundamentals of ornithology New York, John Wiley and Sons, Inc WARt>,P 1969 The annual cycle of the Yellow-vented Bulbul Pycnonotus goiavier in a humid equatorial environment J Zool 157: 25-45 WASER,N.M., AND CALDER,W.a 1975 Possible impairment of nest-building of hummingbirds by acetateleg tags Condor 77: 361 WILEY, R.H 1971 Song groups in a singing assemblyof Little Hermits Condor 73: 28-35 1973 Territorially and non-random mating in Sage Grouse, Centrocercus urophasianus Anim Behav Monogr 6: 87-169 1974 Evolution of social organization and life-history patterns among grouse Quart Rev Biol 49: 201-227 WOLF,L.L 1969 Female territoriality in a tropical hummingbird Auk 86: 490-504 1970 The influence of seasonalflowering on the biology of some tropical hummingbirds Condor 72: 1-14 1975a "Prostitution" behavior in a tropical hummingbird Condor 77: 140-144 1975b Female territoriality in the Purple-throated Carlb Auk 92: 511-522 , F R HAINSWORTH,AND F B GILL 1975 Foraging efficiencies and time budgets in nectar feeding birds Ecology 56: 117-128 , ., , ANDF G STILES 1972 Energetics of foraging: rate and efficiency of nectar extraction by hummingbirds Science 176: 1351-1352 ANDF G STILES 1970 Evolution of pair cooperationin a tropical hummingbird Evolution 24: 759-774 , , AND F R HAn•SWORTH 1976 Ecological organization of a highland, tropical hummingbirdcommunity J Anim Ecol 45: 349-379 , ANDJ S WOLF 1976 Mating systemand reproductive strategy of malachite sunbirds Condor 78: 27-39 WYNNE-EDWARDS, V.C Oliver and Boyd 1962 Animal dispersionin relationto socialbehaviour Edinburgh, 78 ORNITHOLOGICAL MONOGRAPHS NO Heliconia speciesdesignatedby taxon number in Tables 4-7, Figure 20, and elsewhere in the text are describedin a recentpublication (Daniels and Stiles 1979) that appearedtoo late for the names to be changedhere Names assignedare: H-3 •- H mathiasii; H-16 =H umbrophila; H-17 : H sarapiquensis;H-18 =H irrasa H sublataof Figure = H mathiasii. 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Tampa, Florida 33620 (See price list on back and inside back cover.) OrnithologicalMonographs,No 27, viii + 78 pp Editor of AOU Monographs, MercedesS Foster Editor of this number, John William Hardy... Biology, SyracuseUniversity, Syracuse,New York 13210 ORNITHOLOGICAL MONOGRAPHS PUBLISHED THE AMERICAN BY ORNITHOLOGISTS' WASHINGTON, 1979 NO D.C UNION 27 TABLE INTRODUCTION OF CONTENTS MORPHOLOGY... consideredin discussions of the evolutionof lek behaviorin hummingbirds In this ORNITHOLOGICAL TABLE MONOGRAPHS NO 27 MENSURAL CHARACTERISTICS OF PHAETHORNIS SUPERCILIOSUS Sample Sex N ,• SD Range