Observations on the Comparative Behavioral Ecology of Harris' Hawk in Central Chile
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j. Raptor Res. 27(3):143-148 ¸ 1993 The Raptor ResearchFoundation, Inc. OBSERVATIONS ON THE COMPARATIVE BEHAVIORAL ECOLOGY OF HARRIS' HAWK IN CENTRAL CHILE JAIME E. JIMgNEZ• Departmentof Wildlifeand RangeSciences, University of Florida, Gainesville, FL 32611 U.S.A. FABIANM. JAKSI• Departamentode Ecologfa,Universidad Catdlica de Chile,Casilla I Id-D, Santiago,Chile ABsTR•CT.--Throughoutone year we observedthe behavioralecology of Harris' Hawks (Parabuteo unicinctus)in central Chile. The hawks' activity period lacked diel or annual variation. Their most commonflight modewas soaringin thermalsand wind updrafts,rarely usingflapping flight, and never hovering.Harris' Hawks appearedto selectphysiographic features that favoredthe presenceof updrafts, particularlynorth- and west-facing slopes and ridgetops, but werealso commonly seen flying over ravines (wherethey perched frequently). Prey were primarily small- and medium-sized mammals, and secondarily medium-sizedbirds. Although not aggressive,Harris' Hawks were nonethelessattacked by two other sympatricraptors, Black-chested Eagles (Geranoaetus melanoleucus) and Red-backedHawks (Buteopo- lyosoma).These three species,which were studiedover the sameperiod and with the sametechniques, were similar in activityand behavior,although Harris' Hawks were slightlymore differentthan the latter were between themselves. Observacionessobre la ecologiaconductual comparativa de peucosen Chile central RESUMEN.--Porun afio observamosla ecologiaconductual del peuco(Parabuteo unicinctus) en Chile central.E1 periodode actividadde los peucosno difiri6 ni dentrodel dia ni a lo largo del afio. Su modo de vuelomils comfn fue el planeoen corrientest•rmicas y de obstrucci6n,raramento usando el vuelo batidoy nuncael revoloteo.Los peucos parecieron seleccionar caracteristicas fisiogrificas que favoreclan la presenciade corrientesascendentes, particularmente las laderas de exposici6nnorte y oestey las cimas, pero tambi•n se los veia volandosobre quebradas (en dondetambi•n se posaban).Sus presaseran principalmentemamlferos de tamafiospequefio y mediano,y secundariamenteaves de tamafiomediano. Aunquelos peucoseran pocoagresivos, eran atacadospor otrasdos especies simpltridas de rapaces,el iguila (Geranoaetusmelanoleucus) y el aguilucho(Buteo polyosoma). Estas tres especies,que fuerones- tudiadasen el mismoperlodo y conlas mismat•cnicas, eran similaresen actividady conducta,aunque los peucoseran ligeramentemils diferentesque las otrasdos entre elias. [Traducci6n Autores] The Harris' Hawk, Parabuteo unicinctus,is dis- 1980), food-nicherelationships with othersympatric tributed from the southwestern United States in the predators(Jaksifi et al. 1981), and conservationsta- north throughCentral and SouthAmerica to central tus (Jaksifiand Jimgnez 1986). Here we report on Chile and Argentina (Brown and Amadon 1968). aspectsof the behavioralecology of the Harris' Hawk The specieshas been relatively well studiedin North nearits southernmostdistributional limit. This study America (e.g., Mader 1975a, Bednarz et al. 1988 is basedon one year of observationsmade in central and referencestherein). By contrast,little has been Chile concurrentwith thosemade on two other sym- publishedabout the specieselsewhere in Central and patric raptors: Black-chestedEagle (Geranoaetus South America. To our knowledge,the only reports tnelanoleucus;Jimgnez and Jaksic 1989) and Red- come from Chile and cover its diet (Jaksifi et al. backedHawk (Buteopolyosoma; Jimgnez and Jaksifi 1991). Becausethis is the last report of this series, we take the opportunity to make comparisonsbe- • Presentaddress: Department of Biology,Utah StateUni- tween the behavioralecology of the Harris' Hawk versity, Logan, UT 84322 U.S.A. and the two other species. 143 144 JAIMEF•. JIMgNEZ AND FABIAN M. JAI•SI• VOL. 27, NO. 3 STUDY SITE AND METHODS titled with standardprocedures (Marti 1987), as exem- The studysite is describedin Jim•nezand Jaksifi (1989). plified by Jim•nez and Jaksifi(1989) and Pavez et al. Briefly,San Carlos de Apoquindo(33ø23'S 70ø31'W) is a (1992) for sympatricBlack-chested Eagles. ruggedarea 20 km E of Santiagoin the Andeanfoothills with elevationsranging from 1050-1915 m. The physi- RESULTS AND DISCUSSION ographyincludes both flat areasand numerousridges dis- sectedby deepravines. The climateis mediterranean,with Activity levels(measured in minutes) did not dif- cool,rainy wintersand dry, hotsummers. The wind blows fer amongtimes of the day (F = 1.74, df = 5, P > westwardlyfrom the valley to the mountainsduring the 0.12), nor with season(F = 1.73, df = 3, P > 0.16); daytime.The dominantvegetation is an evergreenscrub (very similar to the California chaparral)that changes the interaction betweenthese variables was signifi- physiognomydepending on topographyand orientation. cant (F = 1.91, df = 15, P < 0.03). Indeed, Harris' Based on the number and duration of sightings,the Hawks were observedthroughout the day with no Black-chestedEagle was the mostcommon raptor at the clear peaksof activityin any interval of the day, or site, having been sampled(timed with a stopwatch)for nearly93 hr over a calendaryear (Jim•nez and Jaksifi in any particular season.Thus, Harris' Hawks dif- 1989); the secondmost common raptor was the Red-backed fered from sympatricBlack-chested Eagles, which Hawk, observedfor nearly 29 hr timed (Jim•nez and had a bimodal activity period throughoutthe year, Jaksifi1991). Harris' Hawk rankedthird in this respect, and from Red-backed Hawks, which were more ac- having been monitoredfor 13 hr over the samesample tive during summer and least active during winter. period. Following the same protocol used for the other two Thermal soaringwas the mostcommon flight mode species,for each Harris' Hawk observedwe recorded:1) throughoutthe year, ranging from 47% (winter) to time of observationand duration of activity, 2) activity 16% (summer) of the observedtime (Table 1). Wind type, and 3) habitat beneathbird. We recognizedthe fol- soaringwas the secondmost prevalent flight mode, lowing activity types (cf. Jim•nez and Jaksifi 1989 for detaileddescription): thermal soaring,wind soaring,cruis- accountingfor 37% (fall) to 16% (summer) of the ing, hovering,harassing, perching, and miscellaneousbe- activity time. Harris' Hawks spentmost of their time havior. We recognizedthe followinghabitat types(cf. Ji- perchedduring summer(64%), but very little during m•nez andJaksifi 1989 for detaileddescription): fiatlands, winter (4%). The remainingactivities (Table 1) ac- ravines, ridgetops,and slopes(east-, west-, south-, and countedat the most (during winter) for 19% of the north-facing).We mapped thesehabitats and calculated their surfaceareas (slope-corrected) with a digital planim- daily activity period, and for lessthan 7% during eter from a high-resolutionaerial photograph.The phys- the remaining seasons.It should be noted that our iognomy of each habitat type, in terms of the vegetative samplingtechnique (observing from a hilltop) may coverrepresented by trees,shrubs, herbs, bare ground,and have biasedour detectionstoward soaringbirds and rocks, as well as estimatedprey numbers,were reported in Jim•nez and Jaksifi(1989). away from perchingHarris' Hawks and thosemak- We made observationswith binoculars from the top of ing shortlow flights.Unlike sympatricBlack-chested a hill, from dawn to dusk, with the day divided into six Eagles(Jim•nez and Jaksi• 1989) and Red-backed equal-timeintervals (see Jim•nez and Jaksifi1989). Ob- Hawks (Jim•nez and Jaksifi1991), Harris' Hawks servationstook place during one entire day every other apparently did not hover, and spent little time in week between 1 August 1984 and 1 August 1985. We pooleda total of 780 min of samplinginto four seasons: agonisticinteractions (Table 1). spring (1 August to 30 October), summer (1 November Observed occurrencesof Harris' Hawks (in min- to 31 January), fall (1 February to 30 April), and winter utes) differed both amonghabitat types(F = 18.06, (1 May to 31 July). We usedone- or two-way ANOVA df = 6, P < 0.0001) and amongseasons (F = 3.53, for unequalsample sizes (Sokal and Rohlf 1981:210,360), with PROC GLM in SAS (1985), and the Student-New- df = 3, P < 0.02); there was a significantinteraction man-Keuls test for a posterioricontrasts (SAS 1985:444). between these variables (F = 2.13, df -- 18, P < For analyzing frequency data, we used the G statistic 0.004). Throughout the year, Harris' Hawks flew (Sokal and Rohlf 1981:695). It should be noted that the more often over north-facingslopes (from 59% in assumptionof independenceof data is violatedin behav- summer to 19% in winter), secondarilyover west- ioral studies,because what a bird doesone minute is very hkely to influencewhat it will be doing the next minute. facing slopes,ravines, and ridgetops(from 35% to However, this should affect more strongly comparisons 3% in different seasons),and very little over flat- made within a season than between seasons. Still, the lands, south- and east-facingslopes (Table 2). Ex- P-values calculated should be consideredimprecise and cept for the latter three, there were clear seasonal our interpretations of differencesand similarities taken shiftsin the use of the remaining four habitat types cautiously. We identified prey remains found under perchesand (SNK a posterioritest, P < 0.05 in all cases).West- one nest, and from regurgitated pellets. Prey were iden- facingslopes were usedmore during fall and winter SEPTEMBER 1993 HARRIS' HAWK BEHAVIOR IN CHILE 145 Table 1. Time (in minutes) spentby