The Auk 114(3):396-404, 1997 FORAGING ECOLOGY OF THREE SYMPATRIC TURACOS IN A MONTANE FOREST IN RWANDA CHIN SUN • AND TIMOTHY C. MOERMOND Departmentof Zoology,University of Wisconsin,Madison, Wisconsin 53706, USA ABSTRACT.--Westudied the foragingecology of three sympatrictufacos (Great Blue Tu- raco [Corythaeolacristata], Ruwenzori Turaco [Musophagajohnstoni], and Black-billedTuraco [Tauracoschuettii]) in a tropical montaneforest in Rwandabetween November 1991 and De- cember1992. All three speciesfed primarily on fruit. WhereasBlack-billed Turacos were strictlyfrugivorous, Great Blue and Ruwenzorituracos were partially folivorous;leaves con- stituted25% and 6.3%of their overalldiets, respectively. The overalldietary diversity was highestfor GreatBlue Turacos and lowestfor Black-billedTufacos. Most fruits eaten by tu- racoscame from trees.Although most leaveseaten by Great Blue Turacosalso camefrom trees,leaves eaten by RuwenzoriTuracos mainly camefrom lianasand epiphytes.For the Ruwenzoriand Black-billedtufacos, the two territorialspecies, monthly dietary diversity increasedwith increasingfruit abundancein the environment,but this relationshipdid not hold for GreatBlue Turacos. During periods of fruit scarcity,all threespecies depended more heavilyon theirmost frequently used foods; this trend was particularly evident in the two territorial species.Like most frugivores,these turacos probably were generaliststhat ex- ploited a great varietyof fruit sources.Received 24 June1996, accepted 24 January1997. TURACOS(FAMILY MUSOPHAGIDAE) are large ecologyof theseturacos between 2,000 and birds endemic to woodland and forested habi- 2,500m, where they coexist.Specifically, we tats of sub-Saharan Africa and are considered addressthe following:(1) Whatis the diet com- to be principallyfrugivorous (Brosset and Fry positionfor eachspecies of turaco?(2) Whatis 1988).Given their large body sizeand poten- the dietaryresponse of eachspecies to tempo- tially frugivoroushabits, forest turacos may be ral changesin resourceabundance in the en- important seeddispersers in African tropical vironment? forests.However, the ecologyof mostturacos is poorly known (Dowsett-Lemaire1983, 1990; METHODS Candy 1984;Brosset and Erard 1986;Brosset and Fry 1988).Here, we examinethe foraging Studysite and birds.--The Nyungwe NaturalForest ecologyof threesympatric turacos in a tropical Reserve is a 950-km 2 montane forest located in south- montane forest in Rwanda. western Rwanda, Africa (ca. 2ø35'S,29ø15'E). The Threespecies of turacosoccur in theNyung- generaltopography of the forestis highlydissected, with steepslopes and few levelareas. The studysite we Forest Reserve, Rwanda. The Great Blue Tu- encompassesan area of approximately3.5 km2 and raco(Corythaeola cristata) exists throughout the rangesfrom 1,950to 2,500 m in elevation.Extensive entire elevationalrange of the forest(1,760 to trail systemswithin the study siteprovide access to 2,950 m; Dowsett-Lemaire1990). The Ruwen- the home rangesof all focalbirds studied. zori Turaco (Musophagajohnstoni) is common The Great Blue Turaco weighs approximately between2,000 and 2,920m and may descendto 1,000g and is the largestspecies in the family.The 1,800 m in some wetter areas (J.-P. Vande Great Blue Turaco lives in social groups of 6 to 20 Weghepers. comm.,C. Sun pers. obs.).The individuals (Brossetand Fry 1988,C. Sun pets. obs.). Black-billedTuraco (Tauracoschuettii) is found Fifteenbirds formed the focalgroup that we studied. up to 2,500 m but is more abundantat lower Ruwenzori and Black-billed turacos each weigh elevations and reaches the lowest limit of the about250 g. Individualsof both specieslive in pairs that defend year-round territories (Brossetand Fry forest (Dowsett-Lemaire 1990, C. Sun pers. 1988, C. Sun unpubl. data). obs.).In this paper we comparethe foraging Between November 1991 and December 1992, C.S. followedfocal groupsof turacosmonthly and re- • Presentaddress: Department of Plant Pathology, corded their activities, movements,and diets. Each University of Wisconsin,Madison, Wisconsin 53706, specieswas followed for two to fivedays each month, USA. E-mail: [email protected] during whichdata were collectedfor 25 to 40 h. On 396 July1997] ForagingEcology ofFrugivorous Turacos 397 A A=0.5 C=0.5 Food scores A--1 A=I B=0.5 B--1 B=I B=I C=1 B=0.5 A A B B C B Feeding pattern I I I I I I I I I I I I I I I I I I I I I Time 00 03 06 09 12 15 16 21 24 27 30 min Activity FORAGE B A=0.5 Food scores A=I B=I B=0,5 B=I B=I AAB B B AB B B Feedingpattern,, Time 00 03 06 09 12 15 16 21 24 27 30 min Activity REST I FORAGE--•- F•G.1. Schematicsof activitiesand feedingpatterns of two focalbirds and their food scores. (A) depicts a focalbird activelyforaging, (B) depictsa bird mostlyresting. "Activity" indicates the behavior state of the focalbird during each3-min interval.Dots and linesabove the time barsdepict the feedingpatterns; dots denotefeeding "incident," linesdenote continuous feeding. Letters above each dot or line indicatesthe food type(s)eaten during that feeding episode. "Food scores" records the type of foodeaten and its corresponding scorein each3-min interval. The dashed vertical lines protruding from the time bar (B) divide 3-min intervals into half. average,one group of Great Blue Turacos,2.2 pairs foodtypes eaten by eachbird weregiven a totalscore of RuwenzoriTuracos, and 1.6 pairs of Black-billed of one.If a bird ate two typesof foodwithin a 3-min Turacoswere followedmonthly. Results presented period,each food type was scored0.5 for that bird herewere based on 433,476, and400 h of systematic duringthat interval(Fig. 1A). Wedid not distinguish observationson one group of Great Blue Turacos(15 how long a bird fed on eachfood type during a 3-min birds), four pairs of Ruwenzori Turacos, and two interval.Birds often ate only onefood type duringa pairs of Black-billedTuracos, respectively. foragingbout and never were observedto feed on Recordingactivities.--We used a focal-animalsam- more than two food typeswithin a 3-min interval. pling procedure(Altmann 1974)to documentthe ac- During long restingperiods, a focalbird occasion- tivity patterns of territorial Ruwenzori and Black- ally tookone or two fooditems. Foods taken at such billed turacos. For the Great Blue Turaco, we used a feeding"incidents," when the bird wasnot "forag- focal-group scan sampling procedure.We used a ing," were recordedonly if the feeding occurred 3-min instantaneoussampling method to recordthe during the first half of a 3-min interval (Fig. lB). behavior"states" (Altmann 1974) of focalbirds. Be- Foodeaten at a feedingincident that began in thesec- havior "events" of short duration (e.g. calls and ond half of a 3-min interval would have been record- fights) were recordedas frequencieswithin each ed in the subsequentinterval(s) if the feedinginci- 3-min interval (Martin and Bateson1986). dent turned into a continuous bout that extended Recordingdiets.--A food type wasdefined as a dis- into a subsequenttime interval(s). On average,then, tinct kind of item eatenby turacos(e.g. fruits of spe- foodseaten at thesefeeding incidents were recorded ciesA, leavesof speciesB). Fruits, leaves, and flowers only50% of thetime. Foods recorded at thesefeeding of the sameplant specieswere treatedas different incidentswere scored equally as those recorded dur- food types.To quantifythe differentialuse of food ing continuousfeeding (i.e. when birds were "for- types,we usedthe followingprocedure. When focal aging"). birdswere activelyforaging, the behaviorstate (i.e. By consideringfoods eaten at shortfeeding inci- "foraging") and the numberof foragingindividuals dentsequally with thoseconsumed during contin- wererecorded at 3-min samplingpoints. During the uous feeding,we might have biasedour results. 3-min interval following each samplingpoint, all However,this practicewas necessary given that ob- 398 SUNAND MOERMOND [Auk, Vol. 114 serving several birds simultaneouslynecessitated (numberper ha) of reproductivelymature treesof that we recorddata quicklyand consistently,and we speciesi. For community-widefruit abundancein- could not predict at the outsetwhether a feeding dices,i includesall speciesof treessampled in the would be an extendedfeeding bout or a short inci- phenologysurvey. Because animals use only a subset dent. Our procedurerepresented the best compro- of resourcesin their environment,community-wide misebetween neglecting and overestimating the im- fruit abundanceindices may be a poor measureof portanceof food typeseaten at theseincidents. the quantityof resourcesactually available to a par- Becausethe daily overallnumber of foodtypes eat- ticularspecies. Therefore, we calculatedfruit abun- en by a group or pair of turacosusually was small, danceindices specific to eachturaco species, includ- and the foodtypes eaten at feedingincidents usually ing only plant speciesactually consumedby the were not different from thoseeaten during continu- birds. Unless indicated otherwise, all fruit abun- ous feeding, our samplingscheme was unlikely to danceindices applied in the followinganalyses are havemissed recording the rare food types. the indicesspecific for eachturaco species. Estimatingfruit abundance.--Todocument tempo- Data analyses.--Weused the Simpsonindex (D), ral changesin community-widefruit abundance,we the reciprocalof Simpson,soriginal formula (Simp- conductedmonthly surveys on the phenologyof 568 son 1949), to describedietary diversity of each tu- reproductivelymature trees of 49 species.As part of raco species: a study of seeddispersal