The Hunting Behavior of Black-Shouldered Kites (Elanus Caer Ule Us Le Ucur Us) in Central Chile ’

SHORT COMMUNICATIONS 907 The Condor89:907-911 0 The CooperOrnithological Society 1987 THE HUNTING BEHAVIOR OF BLACK-SHOULDERED KITES (ELANUS CAER ULE US LE UCUR US) IN CENTRAL CHILE ’ FABIAN M. JAKSI~, RICARD~ Row, ANTONIETA LAEIRA, AND JAIME E. JIM&WE Departamento de Biologia Ambiental, UniversidadCatdlica de Chile, Casilla I1 4-D. Santiago, Chile Key words: Hunting behavior;hunting success; hov- recordings,to determinewhether prey items were caught ering; Black-shoulderedKite; central Chile. by the kite, and to keep track of the kite when it flew beyond the rangeofthe nakedeye. We devised a system Kites of the genus Elanus are found throughout the of single-letter key words to record the different be- world principallyin open areassuch as grasslands, sparse haviors of the kites, thus obtaining an alphabetically- shrublands,and agricultural fields (Brown and Ama- codedethogram similar to Walter’s (1983) “actigram.” don 1968). Becauseof their characteristichover-hunt- The recordingswere later played in the laboratory to ing, and their widespreaddistribution, thesekites make time the observations with a stopwatch (precision = interesting subjectsfor analyses of their hunting be- 0.0 1 set). The two teams used the same model of tape havior. Such studies have been conducted in several recorder,and communicatedby walkie-talkiesto avoid regions,including North America (Waian and Stendall confusingthe target birds when flying in the same gen- 1970, Warner and Rudd 1974, Koplin et al. 1980) eral area. Europe (Amat 1979, Heredia 1983), Africa (Tarboton We quantified the behavior of the kites bimonthly 1978. Mendelsohn 1982). and Australia (Baker-Gabb between 1 April 1983 and 24 January 1984, dividing 1984).However, quantitative informationon the hunt- this time spaninto four seasonsas follows: fall (1 April ing behavior of South American kites was nonexistent to 18 June), winter (25 June to 10 September), spring until now, and is reportedhere from a locality in central (24 September to 4 December), and summer (23 De- Chile. cember to 24 January). We obtained a total of 2,613 min (= 43.5 hr) of continuous monitoring of kites. MATERIAL AND METHODS During the fall season,we tracked two kites, but could not make surethat they were the sameindividuals from STUDY SITE day to day, becauseat least four kites were present in We chose the same area from which Meserve (1977) the study area. However, only two individuals win- reported the food habits of Chilean kites (Polpaico: tered, and later nested in the area, thus making us 33”09’S, 70”54’W, about 60 km NW of Santiago by confident that > 75% of our observationswere of only road). Our studysite was composedof three contiguous two individuals of different sex. Black-shoulderedKites fenced agriculturalplots planted initially with alfalfa, are not strongly sexually dimorphic, so we could cat- and later with wheat. Large trees of Prosopischilensis egorizetheir genderonly after they courted and nested, and Acacia cavenwere sparselydistributed in the open and then, by focusing on particular molting patterns, fields. Along the edges,dense rows of poplars (Populus we could determine their sex through spring and sum- sp.) were interspersed with scattered willows (Salix mer. sp.). All four tree species in addition to fence posts We observed that kites in our study area have bi- were used by the kites for perching and feeding, and modal hunting activity periods: early in the morning poplars and willows also for nesting.Black-shouldered (3 to 4 hr after dawn) and late in the evening (3 to 4 Kites in Chile belong to the subspeciesE/anus caeru- hr before dusk). They seemed to spend most of their leus leucurus;miscellaneous information on their bi- day resting,perhaps to a largerextent than nonraptorial ology can be found in Housse (1935), Johnson (1965), birds (see Herbers 1981). During fall and winter, we Meserve (1977) and Schlatter et al. (1980). only worked in the evenings, but during spring and summer both in the morning and in the evening. FIELD TECHNIQUES We formed a four-person field crew with three per- BEHAVIORS ANALYZED manent members (the co-authors of this paper) and We recognizedthe following behavioral categories: different temporary volunteers. These four people in Activeperching. Here, we do not refer to total time turn formed two-person teams, each assignedto a sin- perching,which apparently takes the most substantial gle bird (“focal-animal sampling,”Altmann 1974) with part of the kite’s day. On arriving at the study site we one person recording observationson a tape recorder, started scanningthe field with binoculars. Apparently, and the other provided with binocularsto confirm the kites were hidden in the trees, resting, and thus invis- ible to us. When about ready to start hunting, they moved to a more conspicuous perch and started ’ Received 13 October 1986. Final acceptance 16 grooming themselves for a few minutes. We did not March 1987. startrecording active perchingobservations until a giv- 908 SHORT COMMUNICATIONS TABLE 1. Time allocated(in percentagesof total time TABLE 2. Time allocated(in percentagesof total time recorded)by Black-shoulderedRites to different activ- recorded) by male and female Black-shoulderedRites ities; only evening observations are reported. Results to different activities during spring and summer. Both are for both sexescombined. morning and evening periods are reported. Activity Fall Winter SPnng Summer Morning Evening Seasonand actwity Male Female Male Female Active perching 44.6 34.9 76.8 41.2 ~ Hunting flight - 46.8 37.1 18.1 49.3 Spring Cruising flight 8.6 28.0 3.8 1.1 Active perching 54.6 93.5 84.6 94.4 Other flight* 0.0 0.0 1.3 1.8 Hunting 30.2 0.0 10.1 3.3 Feeding nestlings 0.0 0.0 0.0 6.6 Cruising flightflight 5.1 5.5 2.8 2.0 Time observed Other flight* 10.1 1.0 2.5 0.3 (min) 558.7 71.8 857.7 393.4 Time observed *Courtshipand territorial displays. (min) 300.7 265.1 388.8 242.6 Summer Active perching 22.8 96.9 43.9 38.7 Hunting flight 76.6 0.0 48.8 44.9 en kite took off and returned to a perch. By symmetry, Cruising flight 0.6 3.1 0.9 0.8 we discardedthe last observation of perchingwhen we Other flight* 0.0 0.0 3.7 0.0 decided that a kite was not going to hunt any more Feeding behaviorduring that here period. refers Consequently,to the time spentthe perching active perchingbetween nestlings 0.0 0.0 2.7 15.6 Time observed flights. (min) 131.9 32.1 184.7 134.6 Hunting flight. This includes those hunting bouts between the moment a aiven kite left a verch until it * Courtshipand territorial displays. perched again. We recognizedseveral subcategoriesof hunting flight: (a) hovering: the well-known stationary flight typical ofkites: (b) interhovers:the glidesbetween RESULTS AND DISCUSSION a hovering position and another; (c) strike: the descent Allocation of time by Black-shoulderedRites to dif- from a hovering position to the ground; this behavior ferent activities throughout the year (eveningsonly) is was sometimes punctuated by one or more stops in reported in Table 1. These evening records add up to mid-air before the final descent, but we did not cate- 1,882 min (= 3 1.4 hr) of continuous monitoring (i.e., gorize it as a separatebehavioral act; (d) ground: the 72% of the total observations). The remainder were time spent by a kite on the ground after a strike; (e) recorded during morning periods. Becausekites could pre/posthovering: the time spent by a kite between not be separated by sex during both fall and winter, leaving the perch and the first hover, plus the time results from spring and summer (when kites could be between the last hover and the kite’s alighting on a assignedto either sex) were pooled into an unsexed perch. On three occasions(during spring) we observed categoryto render figurescomparable. Active perching a different hunting technique: aerial pursuit, which a time was constant at about 40% throughout the year, male kite usedfor capturingsmall birds. On four other except for spring, when kites devoted almost twice the occasions(also during spring)we observedperch hunt- time (77%) to this activity. Perhaps the incidence of ing, with a male kite dropping directly from a fence hunting from perchesincreased during this season,but post to the ground;presumably this techniquewas used we have no data to substantiatethis. Time allocated to capture large insects(coleopterans or orthopterans). to hunting flight decreasedfrom fall to spring,returning Cruisingflight. This refers to a fast, direct mid-al- to the original levels during summer, when kites were titude flight, apparentlyused to move betweendifferent raising nestlings.Cruising flight was generally rare ex- perchesor hunting grounds. cept during winter when kites shifted hunting positions Otherflight. This was recordedonly during the pair- more frequently and over greater distances. Perhaps ing and nesting period (spring and summer) involving this reflected the lower availability of prey resources mainly the male. In some casesflight seemed to serve during winter (Glanz 1977, Jaksic-et al. 1981). Other some courtshiv function: it consistedof an aerial dis- fliaht involved courtship or territorial displays. and play in front of the mate, approachingit frontally with was observed only during spring and summer.- a slow flight and with wings flapping in an undulating It was possible to separatebehavioral activities by fashion. Sometimes this approachwas followed by the sex during spring and summer months, when morning transferofa prey item, and its subsequentconsumption observations(73 1 min = 12.2 hr of monitoring) were by the mate. In some other casessimilar aerial displays made (Table 2). The female spent more time perching were made in front of intruding kites, resulting in ex- and less time hunting in flight than did the male, par- pulsion of the intruder (the sex of which we could not ticularly during summer mornings, when the male did determine).

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