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 , 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 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 (“focal- 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 (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). all the hunting. No clear differenceswere observed in Feeding nestlings.This was the time spent by the cruising flight between the sexes.The male was more female (early in the nesting season)passing food to the frequently involved in displays than was the female. nestlings,and by both male and female kites doing so Feeding of nestlingswas observedonly during summer later in the nesting season. evenings,with the female devoting more time than the SHORT COMMUNICATIONS 909

TABLE 3. Duration of different activities of Black-shoulderedRites by season(sexes pooled); only evening observationsare reported. None of the differencesbetween means in (A), (B), (C), or (D) are significant(all Ps > 0.20) by the test of equality of means when the variances are heterogeneous(Sokal and Rohlf 1981:409).

Fall Winter Spring Summer Activity + k 2 SE (see) n 1 + 2 SE (set) n R k 2 SE (set) n R + 2 SE (xc) n

(A) Active perching 339 * 105 44 215?182 7 599 + 212 66 648 + 505 15 (B) Hunting flight 391 + 175 23 250 f 144 5 345 ? 285 4 152 * - 1 Pre/posthovering 119 f 27 112 39 + 18 14 124 + 66 35?- 1 Hovering 115 * 14 460 75 ? 11 61 62 f 14 :: 4*1 4 Interhover 92 + 10 379 56+11 49 34kll 25 5+5 4 Strike 7*3 26 221 8 5&2 2 Ground 11 i9 7 11 *9 3 6*- 1 (C) Cruising flight 58 ? 31 12 1,205 ? - 1 26 + 7 36 2029 13 (D) Other flight* 37 ? 16 10 104254 4 (E) Feeding nestlings 520 f 223 3

*Courtship and territorial displays.

male to this activity. In general, the male was on the and ground) becausethese activities were sequential wing more in the mornings than in the evenings in and constrained by the total time spent in hunting both spring and summer, whereas the female did the flight, which was not significantly different anyway. opposite during summer, with no clear pattern during Consequently,these data are inherently nonindepen- spring. The proximate cause of differential time allo- dent, renderingthem inadequatefor statisticalanalysis cation by the male during the breeding period seemed (Gurevitch and Chester 1986, Swihart and Slade 1986, to be the need to collect enoughprey to feed the female and referencestherein). and nestlings. The incubation period apparently af- Similar results were obtained when scrutinizing the fected how the female used its time; during spring it mean duration of different activities in morning and was hardly seen on the wing, whereas during summer evening periods (Table 4). Except for a significantdif- eveningsit behaved similar to the male. ference observedin mean duration of cruisingflight in Mean duration of different activities throughout the spring,none ofthe other meansdiffered betweenmom- year (using only evening observations) is reported in ing and evening periods. Because mean duration of Table 3. There were no statistically significant differ- specifichunting activities did not vary between seasons encesbetween seasons in either perching,hunting flight, in Black-shoulderedRites, this indicates a relatively cruising flight, or other flight. Rites appearedremark- constantduration of the components of their hunting ably constantin the duration of thesespecific activities. repertoire,independent of climatic conditionsand prey We did not test for differencesin subcategoriesof hunt- abundances. ing flight (pre/posthovering,hovering, interhover, strike, Hunting successof Black-shouldered Rites, how-

TABLE 4. Duration of different activities of Black-shoulderedRites (sexes pooled) in morning and evening periods. There are no significant differences (all Ps > 0.40) between morning and evening periods in either spring or summer in (A), (B), (C) (summer only), or (D) by the test of equality of the means of two samples whose variances are assumedto be unequal (Sokal and Rohlf 1981:411). C differs at P < 0.02 during spring only.

Spring Summer Morning Evening Morning Evening Activitv i k 2 SE (set) n R k 2 SE (set) n R k 2 SE (set) n f k 2 SE (set) n

(A) Active perching 627 f 205 73 599 f 212 66 451 ? 252 9 648 f 505 15 (B) Hunting flight 428 f 287 7 345 & 285 4 990 ? 946 2 152 t - 1 Pre/posthover 171 + 38 45 35 -t - 1 Hovering 67 ? 17 98 12462 + 6614 :: 137167 +-t 273 :: 4*1 4 Interhover 89 + 19 80 341-11 25 125 ? 13 57 5+5 4 Strike 10 * 5 6 5?2 2 6+0 3 Ground 17 -c 5 4 5+- 1 43 i - (C) Cruising flight 79 + 40 23 26 + 7 36 15 ?Z 12 20 & 9 13 (D) Other flight* 48 + 25 8 37 k 16 10 104 * 54 4 (E) Feeding nest- 520 f 223 3 lings

*Courtshipand territorial displays. 910 SHORT COMMUNICATIONS

TABLE 5. Hover-hunting successof Black-shoulderedKites in different currencies(figures in parenthesesare percentages).

Currency Fall Spring

Strikes/hunts 14/23 (61) 315 (60) 23/27 (85) 21/25 (84) Kills/strikes o/14 (0) o/3 (0) 13123(57) 1l/21 (52) Kills/hunts O/23 (0) o/5 (0) 13/27 (48) 1l/25 (44) Minutes/kill 262/O 27/O 246/13 295/l 1 ever, changed markedly throughout the year (Table de1 elanio azul (Elanus caeruleus).Dofiana Acta 5). The number of strikes per hunt was relatively low Vertebrata (Spain) 6(l): 124-128. in both fall and winter (when each kite was hunting for BAKER-GABB,D. J. 1984. The feeding ecology and itself) and higher in springand summer (when the male behaviour of sevenspecies of raptor overwintering was feeding the nesting female). Kills per strike and on coastalVictoria. Aust. Wildl. Res. 11:517-532. per hunt were both surprisingly low during fall and BROWN,L., AND D. AMADON. 1968. Eagles, hawks winter, and much higher during spring and summer. and falcons of the world. Country Life Books, Fel- Kites observedhunting during fall and winter made no thorn, England. kills, but they made a kill every 19 and 27 min on the GLANZ, W. 1977. Small , p. 232-237. In averageduring springand summer, respectively.Black- N.J.W. Thrower and D. E. Bradbury [eds.], Chile- shoulderedKites appearedto be remarkably inefficient California mediterranean scrub atlas: a compar- at hunting when not raising nestlings. ative analysis. Dowden, Hutchinson, and Ross, Provided that the main prey of the kites in the study Stroudsburg,PA. area were the rodentsAkodon olivaceus and Mus mus- GUREVITCH,J., AND S. T. CHESTER. 1986. Analysis culus (Meserve 1977; pers. observ.) the differential ofrepeatedmeasures experiments. Ecology 67:25 l- hunting successof these kites through the seasonswas 255. a likely consequenceof temporal changesin the abun- HERBERS,J. M. 1981. Time resourcesand lazinessin dance of local prey resources. Indeed, both . Oecologia (Berlin) 49:252-262. speciespeak in numbersduring springand summer (cf. HEREDIA,B. 1983. Alimentacibn invemal de1elanio Glanz 1977 and JaksiCet al. 1981 for Akodon sp., azul (E/anus caeruleus)en la provincia de Sala- Ptfaur et al. 1978 forMus sp.), becomingscarcer during manta. Alytes (Spain) 1:255-266. fall and winter. The low numbers of strikes observed HOUSSE,R. 1935. Monografia de1 bailarin Elunus during these latter seasonsmay be a reflection of the leucurusleucurus (Vieillot). Revista Chilena de lower availability of those rodentsin the field. The fact Historia Natural 39:21-24. that most strikeswere unsuccessfulsuggests that winter JAKSI~:,F. M., J. L. Y&Ez. AND E. R. FUENTES.1981. months constitute a survival bottleneck for kites in Assessinga small community in central central Chile. However, given that the two overwin- Chile. J. Mammal. 62:39 l-396. tering kites in our study site remained paired instead JOHNSON,A. W. 1965. The birds of Chile and adia- ofdispersingto communalroosts (Meserve 1977)speaks cent regions of Argentina, Bolivia and Peru. V-01. againstthis interpretation. With increasedprey avail- 1. Platt EstablecimientosGrBficos. Buenos Aires. ability in spring and summer the number of strikes KOPLIN,J. R., M. W. COLLOPY,A. R. BAMMANN,AND (and their success)increased accordingly, in keeping H. LEVENSON.1980. Energeticsof two wintering with the higher impositions of the breeding period. It raptors. Auk 97:795-806. is interesting to recall that the duration of hunting did MENDELSOHN,J. M. 1982. The feeding ecologyof the not vary seasonally(Table 3). Consequently, changes BlackshoulderedKite (Elanus caeruleus)(Aves: in food requirements (breeding vs. nonbreeding)were ). Durban Museum Novitates (RSA) met entirely by changesin hunting yield (successper 13 (part 8):75-l 16. unit time, Table 5). Mendelsohn and Jaksik(unpubl.) MESERVE,P. L. 1977. Food habits of a White-tailed addressthis topic in a comparative study of kite hunt- Kite population in central Chile. Condor 79:263- ing behavior in North and South America, Europe, 265. Africa, and Australia. PBFAUR,J. E., F. JAKSI~,AND J. Y&&z. 1978. Estudio poblacional de Mus musculussilvestre en Santia- We are grateful to J. Agustin Iriarte, Pedro Maldona- go, Chile. Publicacibn Ocasional de1 Museo Na- do, Rodrigo Medel, and Herman Nfifiez, for helping cional de Historia Natural (Chile) 26:3-12. with the observation of kites. We also thank James R. SCHLATTER,R. P., B. TORO,J. L. Y~Ez, AND F. M. Koplin and John M. Mendelsohn for constructivecrit- JAKZX~. 1980. Prey of the White-tailed Kite in icisms on different versionsof this paper. The research central Chile and its relationship to the hunting was funded by grants DIUC 202183 and NSF’s INT- habitat. Auk 97: 186-l 90. 8308032. SOKAL,R. R., ANDF. J. ROHLF. 1981. Biometry. 2nd LITERATURE CITED ed. W. H. Freeman and Co., San Francisco. SWIHART,R. K., AND N. A. SLADE. 1986. The im- ALTMANN,J. 1974. Observational study of behavior: portance of statistical power when testing for in- sampling methods. Behaviour 49~227-267. dependence in animal movements. Ecology 67: AMAT, J. A. 1979. Notas sobrela ecologiaalimenticia 255-258. SHORT COMMUNICATIONS 911

TARBOTON,W. R. 1978. Hunting and the energybud- WALTER,H. 1983. The raptor actigram: a general get of the Black-shoulderedKite. Condor 80:88- alphanumeric notation for raptor field data. Rap- 91. tor Res. 17:l-8. WAIAN,L. B., AND R. C. STENDALL.1970. The White- WARNER,J. S., AND R. L. RUDD. 1974. Hunting by tailed Kite in California with observationsof the the White-tailed Kite (Elunus leucurus).Condor Santa Barbara population. Calif. Fish Game 56: 76~226-230. 188-198.

The Condor89:911-913 0 The CooperOrnithological Society 1987

SEXUALLY MOSAIC PLUMAGE IN A FEMALE AMERICAN KESTREL’

JIMMIER. PARRISH Department of Zoology, 159 WID3, Brigham Young University,Provo, UT 84602 JOANNSTODDARD 4059 Diana Way, Salt Lake City, UT 84117

CLAYTON M. WHITE Department of Zoology, 161 WIDB, Brigham Young University,Provo, UT 84602

Key words: American Kestrel;Falco sparverius;bi- on the inner vane, near the margin, and immediately lateralgynandromorphism;plumage mosaic: endocrine proximal to a broad, subterminal black band. Rectrix abnormality. 5R is virtually identical in color pattern to rectrix 4R. Rectrix 6R is incompletely barred in black on either The plumage of the American Kestrel (F&o sparve- side of the vane with the inner vane more heavily rius) is well recognized to be dichromic between the barred, but the proximal black bars do not meet at the sexes(Meams 1892, Bent 1938, Bond 1943, Friedman rachis. Rectrix 6R terminates in a broad, black band, 1950, Parkes 1955, Cade 1982). On 24 July 1986, a proximal to a rust colored tip. Rectrices 1R to 5R are female American Kestrel was found along a roadside tipped in an ivory/whitish color, typical of males. Rec- in Salt Lake City, Utah, apparently having collided trices 6R, 6L, and 2L to 5L are tipped in a pale rust with an automobile. The right wing was missing, and color, typical of females. Rectrix 1L is tipped in an the bird was emaciatedand generallyin poor condition. ivory/whitish color similar to rectrix 1R. The bird was euthanizedand upon examination showed In general, rectrices 3R, 4R, and 5R are virtually both male and female plumage characteristics(Fig. 1). without female characteristics,with the exception of The breastplumage color pattern was characteristically the incomplete barring on the outer vane margin of female except for the lower left abdominal region (Fig. rectrix 3R. The length of the rectrices does not vary la), where dark brown/black spotting similar to male abnormally, but the vane of rectrices 2R to 5R is ap- breast plumage pattern was present. proximately 2 mm wider than rectrices2L to 5L. None The rectriceswere most aberrant (Figs. la, b, c), and of the tips of the rectricesshow signsof wear (Fig. lc). hereafter are numbered 1 (outermost) through 6 (cen- Basedon crown plumagecharacteristics (Parkes 1955) tral). Rectrix 1 right (1 R) is characteristicof a typical the kestrel was consideredto be a hatch-year bird. female, except the subterminal, black band is consid- The gonadswere paired, not an uncommon condi- erablywider (Fig. lc). Rectrix 2R is incompletelybarred tion that has been found in 30 to 50% of females of with black on the outer vane decreasingproximally to the genusFalco (seeWhite 1969). The left gonad mea- form tiny black spots on the margin. The inner vane sured 1.50 x 1.OO mm and the right measured0.66 x containsonly two partial black bars immediately prox- 0.66 mm. The right gonad was somewhat lighter in imal to a broad, subterminal black band. Rectrix 3R color and smootherin texture than the left, and neither is incompletely barred with black on the outer vane was enlargednor contained enlarged follicles. Results decreasingproximally to form tiny spots as in rectrix of a histological examination of the gonads proved 2R. The inner vane contains only a small black spot inconclusive in determining whether testicular tissue immediately proximal to a broad, subterminal black was present.Visually, both gonadsappeared to be ova- band, typical of males. Rectrix 4R contains no barring ries. on either side of the vane. One small, black spot occurs The occurrenceof sexuallymosaic plumageis some- what difficult to explain, since a variety of systems control secondarysex characteristicsin birds. One case ofgynandromorphism hasbeen reported for the Amer- ’ ’ Received 5 November 1986. Final acceptance 8 ican Kestrel (Brodkorb 1935), and generally refers to April 1987. individuals visually one-half male and one-half female