J. Field Ornithol., 61(1):41-46 PHEASANT CUCKOO FORAGING BEHAVIOR, WITH NOTES ON HABITS AND POSSIBLE SOCIAL ORGANIZATION IN PANAMA KATHRYN E. SIEVING Departmentof Ecology,Ethology, and Evolution Universityof Illinois ShelforalVivarium 606 East Healey St. Champaign,Illinois 61820 USA Abstract.--I describethe terrestrial foragingmaneuver of PheasantCuckoos (Dromococcyx phasianellus)for the first time from 2.5 h of observationon two foragingindividuals in central Panama. Rattling sounds,apparently producedby feather and bill vibrations,ac- companythe first two (of three) phasesof the basicforaging maneuver. These noises, together with body and flight feather movements,may flush organismsfrom coverin the forestlitter, thereby enhancingprey capture rates during the final phase of the maneuver. Pheasant Cuckooswere encountered44 times on a 30 ha censusgrid in lowland secondgrowth forest during 1987 and 1988. Forty percentwere observedon the ground and 60% were perched or flyingin the sub-canopy.My observations,accounts from the literature,and morphological comparisonswith other membersof the Cuculidae indicate PheasantCuckoos are semi- terrestrial.Three intraspecificinteractions suggest one of two likely matingsystems involving intrasexualdominance; male controlof mating and singingareas, or female controlof laying territories containing host nests. COMPORTAMIENTO DE FORRAJEO EN DROMOCOCCYX PHASIANELLUS Y NOTAS SOBRE H•BITOS Y POSIBLE ORGANIZACI(•N SOCIAL DEL AVE EN PANAM.• Sinopsis.--Describola conductade forrajeo terrestrede Dromococcyxphasianellus de la observaci6nde dos avespor un periodode 2.5 horasen Panam/t.Sonidos aparentemente producidospor la vibraci6nde plumasy el pico, acornparianlas primerasdos rases (de un total de tres) de las maniobrasde forrajeo.Los sonidosen uni6n al movimientodel cuerpo y las plumasdel ave,muy bien podrianhacer moverse a los organismosque seencuentran en la hojarazca,facilitando la capturade presuntaspresas por parte del ave en la rasefinal de las maniobrasde forrajeo. Durante 1987 y 1988 se contaron44 avesen un /trea de 30 ha. caracterizadacomo bosque bajo de crecimientosecundario. E1 40% de las aves se observaronen los suelosy el 60% restanteposadas en la vegetaci6no volandoen la parte inferior de la vegetaci6n(sub-docel). Mis observaciones,informes en la literatura y compao racionesmorfo16gicas con otros miembros de la familia Cuculidae,indican que D. phasianellus es semi-terrestre.La observaci6nde tres interaccionesintraespec•ficas sugiere uno de los siguientessistemas de apariamiento:(a) controlpor parte del machode fireasen dondecanta o se aparea, o (b) controlpor parte de la hembra de •treasen dondeaova y que contengan nidos. The PheasantCuckoo (Dromococcyx phasianellus, subfamily Neomor- phinae, Cuculidae)is a broodparasite ranging from southernMexico to parts of Bolivia,Argentina, and Brazil (Hilty and Brown 1986). Though the speciesis not particularly rare, its localizeddistribution and cryptic habits have limited study of its natural history. Basedon analysesof stomachcontents, Sick (1953) suggestedthat PheasantCuckoos obtain arthropodand small vertebrateprey from leaf litter on the forestfloor. Sick alsonoted that PheasantCuckoo foraging behavior had neverbeen 41 42] K.E. Sieving j. FieldOrnithol. Winter 1990 described.I confirm Sick's speculationwith a detailed account of the foraging techniqueused by D. phasianelluswhile searchingfor prey on the ground. The basic maneuver is of particular interest as it involves both soundsand feather movementsthat may flush prey from cover, therebyincreasing feeding efficiency. I alsodiscuss additional observations made from Panama, and accounts from the literature, in an effort to summarizewhat is currentlyknown (or indicated)of PheasantCuckoo natural history, including generalhabits and socialorganization. STUDY AREA AND METHODS I observedPheasant Cuckoos in mature secondgrowth forest (80 to 100 yr old) of Parque Nacional Soberanlaalong the east side of the PanamaCanal, especiallyin moistseepage areas where a generallyopen understoryis interspersedwith densetangles of vinesand bamboo.Dom- inant understoryplants in theseareas include oil palm (Elaeis oleifera), smaller membersof the Palmae, wild pineapple (Aechmeamagdelena), and variousHeliconia species. Other descriptionsof D. phasianellushabitat broadly concur(Smithe 1966, Land 1970, Hilty and Brown 1986). I encounteredPheasant Cuckooswhile walking forest trails on and near a 30 ha grid (50 x 50 m blocks),which enabledme to estimate distances relevant to observations of focal animals. I recorded location and time of day for singingand/or perchedcuckoos. If individualsen- counteredon the grounddid not flush when approached,I followedthem for as long as visual contactcould be maintained, and made observations through8 x 40 powerbinoculars from 10 to 15 m distance.I tape recorded one focal individual using a Marantz cassetterecorder with a Sony di- rectional microphone. RESULTS AND DISCUSSION Foragingbehavior.--On 14 May 1987 from 1700 to 1720 EST and on 31 Jan. 1988 from 1300 to 1515 h I observedsolitary PheasantCuckoos on the forestfloor engagedin stylizedand repetitive foraging sequences. On both occasionsmy attentionwas drawn by a low, "fiuttery," rattle, apparently producedby a combinationof wing and tail feather vibration and bill-clapping. Fluttering noisesaccompanied the first two of three distinctphases to the foragingmaneuver (see below). I tape recorded77 maneuverswhile following the secondforaging cuckooencountered. During the first phase,or "bob" (seeFig. 1), a foragingcuckoo stands in one place with its body, wings, and tail bobbingup and down; the movementssynchronized on the downbeat with pulsesof rattling noise. Pulsesand bobs occur once or twice per second,up to four times. The bird's head is level with its back and the neck is contracted. Its white- tipped tail is fanned and infrequently brushesthe litter surface.Then, for one second,the bird pauses;sound and movementsubside briefly beforethe secondphase ("rush"). During the "rush," the cuckooruns straight forward for 4-12 short, quick steps;its head outstretchedand low. The primaries, partially ex- Vol.61, No. 1 PheasantCuckoo in Panama [43 bob rush I I, I ,I ! ! seconds FIGURE1. Sonagramof the first two phasesof a PheasantCuckoo foraging maneuver with field sketches(above) indicating general postures and movementsduring eachphase. tended out and downward from the body, show small white patches (otherwiseconcealed) and flick forward intermittently.The alula is dis- tinctly visiblein front of the primaries.The lower mandibleclaps against the upper very rapidly, more visiblythan during the "bob." The fluttery rattle noiseincreases in intensitythroughout the "rush," without pulsing, as shownby a sonagram(Fig. 1). After 0.5-2 s the bird abruptly halts, all noise and movementscease, and the final phase is initiated. In phasethree ("peck"), foragingPheasant Cuckoos may peck in the litter, captureprey items,or just look at the groundwhile walking. This stagemay last 2-15 s, occasionallylonger if prey require excessivehan- dling, beforeanother "bob-rush-peck" sequence commences. The average "peck" period of the tape recordedanimal was 6.8 s (n = 77, SD = 2.8 s). Approximately half of this individual's "peck" phasesinvolved an actual peck, or attemptedprey capture. In low-light forest conditionsI was able to identifyonly the followingprey itemstaken; one smallAnolis limifrons(or gecko)and 17 unknown arthropods. Experiments would help determine whether the feather movements and rattle soundsimmediately preceding the "peck" actually facilitate predationby flushingprey. The cuckoo'smaneuver does, however, share elementsof techniquesused by other speciesto flush prey. American Redstarts(Setophaga ruticilla) and Sulfur-rumpedFlycatchers (Myiobius sulphureipygius)wing-flick and tail-fan while walking alongbranches in searchof arborial insects(Ehrlich et al. 1988, Ficken and Ficken 1962, Hilty and Brown 1986, Robinsonand Holmes 1982). Similarly, Greater Roadrunners(Geococcyx californianus) often splay their flight feathers 44] K.E. Sieving J.Field Ornithol. Winter ]990 explosivelyto startleintended insect or lizard prey from cover(Bent 1964). (Closely related Striped Cuckoos[Tapera naevia]spread their primaries and alula-fiick when displayingfrom branches(Wetmore 1968), but to my knowledgenot while foraging.)With respectto soundproduction, Rufous-ventedGround-cuckoos (Neomorphus geoffroyi) bill-snap loudly as they feed at army ant swarms(Hilty and Brown 1986), but whether this enhancescapture efficiencyis unknown. To establishif non-vocal soundproduction I observedis usedto flushprey, playback tape recordings of Pheasant Cuckoo soundsto litter organisms, and measurementof feedingsuccess of cuckoossilenced in someway might be instructive. Generalhabits.--Eighteen (40%) of 44 individualsI observedduring May 1987 and January-June 1988 were either foraging on the ground (as noted), running away from me through the undergrowth,or in the act of flushingfrom the litter to horizontalperches 2-15 m high.Twenty- four singingand two silentindividuals were seenflying or perchedin the sub-canopy.Previous authors agreed that PheasantCuckoos are some- what terrestrial(Sturgis 1928, Wetmore 1968). My observationsindicate the bird is habitually so, foragingfor hourseach day in the leaf litter. Morphologicalcharacteristics of D. phasianellusgenerally support ob- servationalindications of terrestrial habits. Comparedto cuckoosthat run fast and far on open