j. RaptorRes. 30(4):237-239 ¸ 1996 The Raptor ResearchFoundation, Inc. DIET OF LONG-WINGEDHARRIER (CIRCUSBUFFONI) IN SOUTHEASTERN BUENOS AIRES PROVINCE, ARGENTINA MAid• S. BO, S•d'4D• M. CICCHINO, AND MARIANO M. MARTiNEZ Departamentode Biologia,Facultad de CiendasExactas y Naturales,Universidad Nacional de Mar del Plata, Funes3350-(7600) Mar delPlata, Argentina Key Words: Circus buffoni; long-wingedharrier, diet;, t'ro- hair, dentaries and exoskeletons,and compared with phic nichebreadth; Argentina. specimensin collectionsof Museo de CienciasNaturales de La Plata, Museo de Ciencias Naturales "Lorenzo Scag- The long-wingedharrier (Circusbuffoni) is widespread lia" de Mar del Plata and Laboratorio de Vertebrados, in South America ranging from Venezuela to Chubut Facultad de CienciasExactas y Naturales-UniversidadNa- cional de Mar del Plata. All remains in a collection were Provincein Argentina, occasionallyreaching as far south as Tierra del Fuego (Nores and Yzurieta 1980) and cen- lumped and prey items were identified using known rem- tral Chile (del Hoyo et al. 1994). Found throughout Ar- iges,rectrices, bills and bonesof birds and fur, skull parts gentina in open fields,grasslands, savannas, marshes, wet- and feet of mammals.This procedureminimized the pos- lands and ponds from sea level to 690 m elevation(Ca- sibility of overcounting numbers of individuals of each nevari et al. 1991, De la Pefia 1992, del Hoyo et al. 1994), species(Reynolds and Meslow 1984, Marti 1987). Most it is most abundant in the Chaco-Pampeanzone of Ar- prey were identified to the specieslevel. gentina, Uruguay and Brazil (Grossman and Hamlet Adult bird and mammal weights were obtained from the literature (Fiora 1933, De la Pefia 1987, Salvador 1964). Studiesof the long-wingedharrier havefocused mainly 1988, 1990, Navas1991, Camperi 1992) and unpublished on •ts nesting biology (Naroskyand Yzufieta 1973), and data of Kittleim, Comparatore and Barbini, and in the Museo de Ciencias Naturales "Lorenzo Scaglia" de Mar there is only descriptiveinformation on its diet (De la del Plata. Following Pavez et al. (1992) and Jim•nez Pefia 1985, Canevari et al. 1991, Ltpez 1993, del Hoyo (1993), a weight of 1 g was assignedto each insect prey et al. 1994) and hunting habitats (Naroskyand Yzurieta species.When the sex of prey could not be determined, 1973, 1988, De la Pefia 1985). The objectiveof this study the mean weight of males and females was used. Geo- was to determine the diet and niche breadth of long- metric mean (+SE) weight for total prey was calculated winged harriers in the Pampaszone of Argentina. (Marti 1987) and Levins' index of niche breadth (Marti Our studywas conducted in the Lagunade los Padres 1987) was calculated as: Integral Reserve (37ø56'S,57ø44'W) 16 km west of Mar del Plata City, BuenosAires Province.The reserve covers 1 a 680 ha area with low hills and plains. Mean annual B= •-p• temperatureis 13.8øCand mean annual precipitationis *=1 nearly 5 cm. Harriers selectedfor studywere located in a 87 ha area within the reserve called the "El Curral" where Pi is the proportion of individuals in each prey Intangible ReserveZone. It consistsof a mosaicof shrub- category.B varies from 1 to N with N being the number land habitat with native "curro" (Colletiaparadoxa), ex- of prey categories.If prey are equallycommon in all cat- oUc blackberry (Rubusulmifolius) and modified Pampean egories,then B = N; if all prey belong to only one cate- grasslandcomprised of Stipa spp., Bothriochloaspp., Co- gory, B = 1. mumspp. and Carduusspp. (Cabreraand Zardini 1978). We located 4 and 2 pairs of breeding harriers in 1992- Cultivated fields, pastures,tree plantations (mainly Eu- 93 and 1993-94, respectively,and made a total of 46 pel- calyptus)and suburban zones surround the study area, lets and 28 prey remains. Pellets averaged41.8 +_ 10.4 and it is only 400 m from Laguna de Los Padres,where mm (_+SD)in length and 17.9 + 2.9 mm wide (N = 38). there is a large concentration of breeding, aquatic birds A total of 98 prey items wasidentified from 3 taxonomic •ncluding brown-hooded gulls (Larus maculipennis), classesincluding 22 vertebratespecies and 2 insectorders wh•te-faced ibises (Plegadischihi), snowy egrets (Egretta (Table 1). Levins' Index (B) of niche breadth was 7.9 (N thula), cattle egrets (Bubulcusibis), black-necked swans = 25, minus unidentified prey). (Cygnusmelanocorypha) and coots (Fulicaspp.). Birdsaccounted for 79.5% of the total prey items,fol- During springsand summersof 1992-93 and 1993-94, lowed by mammals (17.5%) and insects (3%). Among pellets and prey remains were collectedevery 5-6 d at birds,passefines were the mostcommon (61%) prey re- nest sites,plucking stationsand roostsof breedingpairs mains found. Most passefinesbelonged to the Embefizi- of long-winged harriers. Bird, mammal and insect re- dae (40%), with rufous-collaredsparrow (Zonotrichia capen- mmns were identified based on bones, feathers, bills, sis)the most abundantspecies. Ffingillids, mainly hooded 237 238 SHORT COMMUNICATIONS VOL. 30, NO. 4 Table 1. Percent frequency of prey items, weight of in- siskin(Carduelis magellanica), made up 11% of the diet. dividual prey and total percent biomassof prey in the Among mammalianprey, rodentswere the most numer- diet of breeding long-wingedharriers in southeastern ous (9%) with Akodonazarae the most commonspecies BuenosAires Province,Argentina. Percentagesbased on followedby lagomorphs(6%) and marsupials(1%). a total of 98 prey items. Long-wingedharriers preyed on a wide range of prey ADULT % sizeswith weightsranging from a low of 1 g in the case % FRE- WEIGHT TOTAL of insectsto a high of 450 g in the caseof the white-faced PREY QUENCY (g) BIOMASS ibis. Geometricmean weight of prey was 32.4 - 11.2 g (_SE). By weight, birds comprised the majority of the Birds 79.5 68.6 prey biomass(68.6%). White-facedibises contributed the Tinamidae greatest biomass (19.8%) followed by rufous-collared Nothura maculos 2.0 240 7.0 sparrow(8.8%), spottedtinamou (Nothuramaculosa, 7%), Nothuramaculosa (egg) 2.0 20 0.7 picazuropigeon (Columba picazuro, 6.2%) and eareddove Threskiornithidae (Zenaidaauriculata, 5.7%). Mammalscomprised 31.4% of Plegadischihi 3.0 450 19.8 the prey biomasswith juvenile European hares (Lepusca- Anatidae pensis)contributing the largestamount (26.4%). Insect Anassp. (chick) 3.0 80 3.5 Rallidae biomasswas very low (<0.1%) in the diet. Our resultsare similar to thoseobserved for Montagu's Rallussanguinolentus 1.0 162 2.4 Columbidae harrier (Circuspygargus), marsh harrier ( C. aeruginosus) and hen harrier (C. cyaneus),which also prey mainly on Columbapicazuro 2.0 213 6.2 Zenaida auriculata 3.0 128 5.7 birds (Gonz/tlezL6pez 1991). During the breeding sea- Furnariidae son, diets of marsh and hen harriers can consist of as Phleocryptesmelanops 1.0 16 0.2 muchas 70% birdsby frequencyof occurrence(Schipper Mimidae 1973,Witkowski 1989, Gonz/tlezLOpez 1991, del Hoyo et Mimus saturninus 1.0 74 1.1 al. 1994). Several authors (De la Pefia 1985, 1992, Ca- Emberizidae nevariet al. 1991) havementioned that long-wingedhar- Sicalis luteola 5.0 16 1.2 riers hunt mainly in wetlands,ponds and marshes.The Sicalissp. 2.0 16 0.5 type of prey in our studywas mainly from terrestrialhab- Zonotrichiacqpensis 27.5 22 8.8 itats (91%) and wasprobably related to the fact that cul- Unidentified egg 1.0 2 0.1 tivatedfields, pastures,and tree plantationssurrounded Icterinae the study area. Molothrus bonariensis 1.0 62 0.9 Molothrus badius 1.0 53 0.8 RESUMEN.--Seestudi6 la dieta del gavil•mplaneador (Czr- Pseudoleistes virescens 1.0 71 1.0 cusbuffoni) durante dos periodos reproductivosen la Re- Sturnellasuperciliaris 1.0 53 0.8 servaIntegral Laguna de Los Padres,Provincia de Bue- Carduelismagellanica 11.0 15 2.4 nos Aires. E1 area de nidificaci6n se encuentra en un Ploceidae ambiente arbustivo,circundado por camposcultivados, Passer domesticus 4.0 31 1.8 pasturas,montes, lagunas y ambientes suburbanos.Se Unidentified passeriformes 4.0 21a 1.3 analizaron46 egagr6pilasy 28 restospresa, provenientes Unidentified birds 2.0 96 b 2.8 de seisparejas nidificantes. Se identificaron98 itemspre- Mammals 17.5 31.4 sa, correspondiendoel 79.5% alas aves,el 17.5% a los Leporidae mamiferosy un 3% a los insectos.La amplitud de nicho Lepuscapensis (young) 6.0 300 26.4 tr6fico (B) rue de 7.9 (N = 25). Los paseriformesfueron Cricetidae las wesasm/rs consumidas (61%), dentro de lascuales el Oxymycterusrufus 2.0 70 2.0 Akodon azarae 4.0 21 1.2 chingolo (Zonotrichiacapcrisis) y el cabecitanegra com6n ( Carduelismagellanica) fueron las especiesm/rs frecuentes. Oryzomysflavescens 2.0 17 O.5 Unidentified cricetidae 1.0 36 c 0.5 La media geom6tricadel pesode presasconsumidas rue de 32.4 + 11.2 (+ ES). En cuanto a la biomasaaportada, Didelphidae las avesy los mamiferoscontribuyeron en un 68.6% y Monoddphisdimidiata 1.0 16 O.2 Unidentified mammals 1.0 31 a 0.4 31.4%, repectivamente.La dieta del gavil/mplaneador Insects 3.0 <0.1 mostr6 similitud con la de otras especiesdel g6nero Czr- cu$. Coleoptera 2.0 <1.0 <0.1 Odonata 1.0 <1.0 <0.1 [Traducci6n de Author] Average of the 4 most common identified passerinebirds. ACKNOWLEDGMENTS Averageof all identified birds. Average of the 3 identified cricetids. We thank E. Madrid and R. Caceres for their valuable Averageof the identifiedcricetids and Monodelphisdimidiata. help in the field, A. Vasallofor the assistancein mammal DECEMBER 1996 SHORT COMMUNICATIONS 239 identification, and A. Gavio, M. Favero and M. Zfirate for LOPEZ,H.E. 1993. Algunasobservaciones en Villa Gesell, their comments and suggestions.N. B6 and C. Darrieu, BuenosAires. PredaciCnde Circusbuffoni sobre Zena- curators of the Museo de Ciencias Naturales de La Plata, ida. Nuestras Aves 29:30. and S. Casertano and D. Romero of the Museo de Cien- MARTI,C.D. 1987. Raptor food habitsstudies. Pages 67- cms Naturales "Lorenzo Scaglia", allowed accessto col- lectionsunder their care.The continuedsupport of J.