THE AUK A QUARTERLY JOURNAL OF ORNITHOLOGY VoL. 100 J^•qv^I•¾1983 No. 1 FRUGIVORY AND POLYGAMY IN BIRDS OF PARADISE 1 BRUCE BEEHLER• Departmentof Biology,Princeton University, Princeton, New Jersey08544 USA ABSTRACT.--Istudied fruit-feeding by nine speciesof birds of paradisein Papua New Guinea from July 1978through November 1980and gathered1,187 recordsof foragingat 31 speciesof treesand vines from 14 botanicalfamilies. Fruit consumedwas consistentlysmall- to moderate-sized (mean: I cm diameter), but fruit of different speciesof plants showed high morphologicaldiversity. I classifythe fruit of 31 plant speciesinto three morphological groups:capsule, fig, and drupe/berry.Each of the primarily frugivorousbirds of paradise was recordedtaking fruits from 10-21 plant species,including representativesfrom each class. The monogamousTrumpet Manucode and Crinkle-collaredManucode were fig specialists. More than 80% of their diet was figs. The polygamousspecies of paradisaeidswere more "generalized"fruit-feeders and took significantamounts of fruit from all threemorphological categories.The most important types of fruit among the polygamousbirds were capsular species(49% of diet). While fig specieswere visited by birds from many families, most nonfig trees hosted a narrower range of foragers,and two speciesof trees, Chisocheton weinlandii(Meliaceae) and Gastoniaspectabilis (Araliaceae), were visited only by birds of paradise. The frugivoroushabits of birds of paradiseare similar in severalrespects to thoseof the neotropicalcotingids and manakins.It is arguedthat while frugivory is an important com- ponent of the evolutionof polygamousarena display in thesebirds, it cannot,by itself, explain why some birds are polygamousand others monogamous.Frugivory in the tropics is a complexsyndrome that offers a number of ecologicalalternatives that, in turn, promote different behavioraladaptations. Received 22 March 1982, accepted30 June1982. D. SNOW (1962a, b, 1971a, b) and B. Snow which malesare emancipatedfrom the nestand spend (1970, 1972, 1973, 1977) in their studies of the most of their time in epigamic display.... It is neotropical cotingas (Cotingidae) and mana- probablethat the evolution of the birds of paradise kins (Pipridae) discoveredan apparentrelation in the Australianregion was made possibleby a sim- ilar relationship between the birds and their food linking the habit of fruit-eating to non-pair- supply. bonding polygamy. D. Snow (1980: 1197) writes: There are fundamental differences between the demandsof frugivory and those of insec- Probably as a consequenceof the very nutritious tivory. Insectsare elusive, dispersedthrough fruitsthat they eat, and of theshort tim e perday that the habitat, and difficult to harvest, while fruit they need spendin foraging, somespecialized neo- tropical frugivores have evolved social systemsin is locally abundant, "patchy," and relatively simple to harvest in quantity (Lill 1976). Ani- mals that forage for insectsmust spend a large • Dedicated to the memory of J. Linsley Gressitt, portion of eachday satisfyingtheir dietary de- founder of the Wau EcologyInstitute. 2 Present address: MNH 114 (NHB Room 336), mands, while frugivorescan quickly fill their Smithsonian Institution, Washington, D.C. 20560 cropswith fruit and invest the remaining day- USA. light hoursin other activities,such as self-ad- The Auk 100: 1-12. January 1983 2 BRUCEBEEHLER [Auk, Vol. 100 TABLE1. The birds of paradiseencountered at fruit treeson the Mount Missim study site. Abun- Englishname • Latin binomen Weightb Wingc dance• Crinkle-collaredManucode Manucodiachalybatus 183 + 18 (3) 173 _+8 2-3 Trumpet Manucode M. keraudrenii 171 + 10 (8) 169 _+4 7-10 MagnificentRiflebird e'f Ptilorismagnificus 194 _+16 (2) 187 _+2 1-2 Black-billed Sicklebill Epimachusalbertisii 108 (1) 156 1-2 Superb Bird of Paradiseg Lophorinasuperba 89 _+ 5 (4) 136 _+2 2-4 Lawes' Six-wired Bird of Paradise Parotia lawesii 166 _+ 4 (4) 158 _+4 4-5 MagnificentBird of Paradise Diphyllodesmagnificus 90 + 8 (12) 112 + 2 6-7 RaggianaBird of Paradise Paradisaearaggiana 246 _+12 (3) 181 _+2 5-6 Blue Bird of Paradiseg P. rudolphi 178 (1) 156 1-2 • Nomenclaturebased on Diamond (1972)with someemendations to be used in a checklistof New Guinea birds presentlyin preparation(B. Finch, H. Bell, and B. Beehler). •' Data includeweights of adult malesonly; listed are meanweight, SD, and samplesize. ½Males only; wing arc. dAbundance as measuredby the numberof individualsobserved using a fruiting tree duringa singleday. • Weightsfrom Gilliard and LeCroy(1967). f Wing measurementsfrom skins of threeadult males,preserved as studyskins, National Museum of NaturalHistory, Washington, D.C. • Data from Diamond (1972). vertisement, mate competition, and defense of as well as interspecific differences, and com- a territory, display perch, or mate(s) (Snow pare theseobservations with thosefor frugivo~ 1976, Foster1977). The logic of this argument rous songbirdsfrom the neotropics.Finally, I is persuasive,although the generalizationas I examine the characteristicsof fruit eaten by have presentedit is oversimplified.The rela- polygamousarena-displaying birds and com- tionship between fruit-eating and polygamous ment on the relation of diet to behavior. arena-displayis supportedby the simple ob- servationthat the vast majority of polygamous STUDY AREA AND METHODS arena birds in the humid tropics are fruit-eat- I studiedbirds of paradiseon a 17-haplot of forest ers (Snow 1976,Bradbury 1981). on the southwestslopes of Mount Missim, at about Several authors have shown that fruit is a 1,430 m. The site is 9 km north-northeast of Wau, prominent part of the diet of some speciesof Morobe Province, Papua New Guinea (7ø16'S, birds of paradise (Rand 1940, Gilllard 1969, 146ø42'E).I worked on this site from July 1978 to Schodde 1976), and, in a few instances,the fruit November 1980, for 249 field-days.The study-siteis consumedby these birds has been identified mature Pre-montane Moist Forest (Holdrige et aL botanically(Cooper and Forshaw1977, LeCroy 1971) on highly dissectedand well-drained ridge- et al. 1980). To date, however, no systematic and-ravine topography.The area receivesan annual rainfall of about 2,000 mm (McAlpine et al. 1975) in accounthas been published on frugivory by a moderatelyseasonal pattern, with more rain falling birds of paradise. from November to April. The 17-ha site supports While studying the behavior and ecologyof about 80 speciesof trees and a community of about four speciesof birds of paradise in the moun- 125 speciesof resident birds. The plot is unusual in tains of centralPapua New Guinea, I gathered having nine residentbirds of paradise(Table 1). A data on fruit-eating by all bird speciessharing tenth species,Loria's Bird of Paradise(Cnemophilus fruit resourceswith these birds of paradise. The loriae), is an occasionalvisitor. Additional details on avian fruit-eating community included more the habitat and biota of the study-site are presented than 30 speciesof birds. In this paper I docu- elsewhere (Beehler 1983). ment the types of fruit eaten by nine species I documentedthe diet of the birds by: (1) recording of birds of paradise (Table 1) that share this birds visiting fruiting trees, and (2) collectingand mid-montane study-site,and I show that, while •dentifyingthefruit remains in fecal samples taken from captured birds. I made repeated observations the fruit-crop of some trees is consumedby a of fruit-feeding at plants producingfruit eaten by wide range of avian foragers, certain tree birds of paradise.In the early monthsof the study I speciesproduce fruit eatenmostly, and in some monitoredvisits by birds to many speciesof fruiting instanceswholly, by birds of paradise.In the plantsthat my researchassistants encountered in the discussionI point out somefamily-wide trends, forest.When I found a tree or vine that was regularly January1983] Frugivoryin Birdsof Paradise 3 visited by birds of paradise, I began making stan- speciesof birds of paradisethat thesewere not lost dardized observations. I recorded all birds that en- in the sampling bias. tered the tree to feed; for selectedspecies of para- The unit of measurein this projectwas the "feed- disaeidsI recordedlength of feeding-bouts,number ing-bout": a recordof a bird enteringa tree and tak- of fruit consumed, and interactions with other for- ing at leastone fruit. I discoveredearly in the study agers.I was assistedin this work by two field tech- that birds of paradiseforaged for fruit in a behav- niciansemployed to find new treesand to help with iorally stereotypedfashion (see Resultssection). the foragingcensuses. Their help madepossible the Consequently,I treat paradisaeidforaging bouts as simultaneous observations of avian foraging at sev- equivalent. Avian use of fruit resourcesare quanti- eral fruit-trees. fied and comparedin terms of theseforaging bouts. We recordedfruit-foraging by sittingnear the fruit- I collectedadditional data on fruit eatenby birds tree and watching birds enter, feed, and depart. We of paradiseby examiningfecal samples. I mist-netted identified birds using 7 x 35 and 8 x 44 binoculars, birds and placed them in a darkenedholding cage as well as a 157<telescope, depending upon the con- with a wire-mesh floor of 1/z-inch hardware screen. ditions. We timed observationswith digital watches. Beneaththis was a tray with an aluminumfoil liner We observedat treesin the early morning, usually that trappedall excreta.Some of the materialtrapped for periods of 1.5-2.5 h, depending upon the