BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofitpublishers, academic institutions, research libraries, and research funders in the common goal of maximizing access tocritical research.

Food Habits of the Roadside Hawk (Buteo magnirostris)During the Nonbreeding Season in the Southeastern Pampasof ArgentinaAuthor(s): Alejandro V. Baladrón, María S. Bó, Ana I. Malizia, and Marc J.BechardSource: Journal of Raptor Research, 45(3):257-261. 2011.Published By: The Raptor Research FoundationDOI: http://dx.doi.org/10.3356/JRR-10-108.1URL: http://www.bioone.org/doi/full/10.3356/JRR-10-108.1

BioOne (www.bioone.org) is a nonprofit, online aggregation of core research in thebiological, ecological, and environmental sciences. BioOne provides a sustainableonline platform for over 170 journals and books published by nonprofit societies,associations, museums, institutions, and presses.

Your use of this PDF, the BioOne Web site, and all posted and associated contentindicates your acceptance of BioOne’s Terms of Use, available at www.bioone.org/page/terms_of_use.

Usage of BioOne content is strictly limited to personal, educational, and non-commercial use. Commercial inquiries or rights and permissions requests should bedirected to the individual publisher as copyright holder.

J. Raptor Res. 45(3):257–261

E 2011 The Raptor Research Foundation, Inc.

FOOD HABITS OF THE ROADSIDE HAWK (BUTEO MAGNIROSTRIS) DURING THE NONBREEDING SEASON IN

THE SOUTHEASTERN PAMPAS OF ARGENTINA

ALEJANDRO V. BALADRON1

Laboratorio de Vertebrados, Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Mar del Plata, Funes 3350,B7602AYJ Mar del Plata, Argentina

and

Consejo Nacional de Investigaciones Cientıficas y Tecnicas — CONICET, Rivadavia 1917, C1033AAJ Buenos Aires,Argentina

MARIA S. BO AND ANA I. MALIZIA

Laboratorio de Vertebrados, Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Mar del Plata, Funes 3350,B7602AYJ Mar del Plata, Argentina

MARC J. BECHARD

Boise State University, Raptor Research Center, Department of Biology, 1910 University Drive, Boise, ID 83706 U.S.A.

KEY WORDS: Roadside Hawk; Buteo magnirostris; Argen-tina; diet; nonbreeding diet; pampas; small mammals.

Studies of raptors’ diet are important for understandingthe ecological relationships of the raptors themselves, aswell as for assessing the influence of these predators oncommunity ecology (Marti et al. 2007). Although there isabundant information about food habits of raptor speciesaround the world, data on the trophic ecology of neotrop-ical raptors are scarce and the diets of many species arepoorly known (del Hoyo et al. 1994, Bierregaard 1998, Boet al. 2007).

The Roadside Hawk (Buteo magnirostris) is a widespreadraptor species of Central and South America, ranging fromnorthern Mexico to Rıo Negro Valley in central Argentina(Thiollay 1994). This medium-sized raptor usually inhabitswoodlands and forest edges and, to a lesser extent, openfields near woodlands (Canevari et al. 1991). Near thesouthern boundary of its range, in the pampas of BuenosAires Province (Argentina), this raptor is also associatedwith agroecosystems and grasslands (Narosky and Di Gia-como 1993, Mazar-Barnett and Pearman 2001).

Despite being a common species with broad distribu-tion, the Roadside Hawk has been little studied and infor-mation about its food habits is scarce and mostly limited toqualitative and anecdotal information (e.g., Haverschmidt1962, Massoia 1988). In two studies, the diet of RoadsideHawks was quantitatively analyzed. Panasci and Whitacre(2000) reported breeding-season diet in Guatemalathrough direct observation of nests, and found that the

Roadside Hawk delivered mainly small vertebrates(.90%; mainly lizards, frogs, and rodents) to the nest.However, Beltzer (1990) analyzed stomach contents of 22Roadside Hawks in Argentina throughout one year, anddetermined that they consumed mostly insects (77%,mainly orthopterans).

The objectives of our study were to quantitatively de-scribe the diet of the Roadside Hawk and to estimate itsfood-niche breadth during the nonbreeding season in Ar-gentina.

METHODS

Our study was conducted in Mar Chiquita BiosphereReserve (southeastern Buenos Aires Province, Argentina;37u329 – 37u459S; 57u199 – 57u269W), a part of the PampeanFitogeographic Region (Cabrera 1971, Viglizzo et al. 2006).The landscape in this region was dominated by temperategrasslands, but the original gramineous vegetative commu-nity has been highly modified by the development of agri-culture (Cabrera 1971, Bilenca and Minarro 2004). TheReserve comprises a 4600-ha coastal lagoon surroundedby native halophytic grasslands, including a diverse arrayof natural vegetation, such as marshes, coastal dunes, andnative forests (Stutz 2001). This habitat heterogeneity sup-ports a high faunal diversity, which represents a wide spec-trum of potential prey for raptors (Martınez 2001). Specif-ically, our sampling was conducted in an area of tala (Celtistala) forest at Nahuel Ruca Ranch. The tala forest is a typeof thorn forest (Espinal) and is considered threatened dueto indiscriminate extraction, cattle grazing, and agriculture(Torres Robles and Tur 2006). This relict patch (6 ha)1 Email address: abaladro@mdp.edu.ar

SEPTEMBER 2011 SHORT COMMUNICATIONS 257

represents the southernmost extreme of Espinal forest inArgentina, and is surrounded by a pond and grazed nativegrasslands, which represent potential hunting areas forraptors (Isacch et al. 2000). Adult and juvenile hawks (ap-proximately 10 individuals) were often observed in the talaforest during preliminary surveys.

During nonbreeding seasons 2006–08 (March to Sep-tember), we collected pellets on 18 occasions at hawks’roost sites we had previously identified within the tala for-est. We placed pellets in labeled plastic bags. We latermeasured the pellets to the nearest mm (length andwidth) and soaked them in water to separate osseous andchitinous materials. We calculated the average number ofprey items per pellet.

We classified prey to the lowest possible taxonomic level.We identified mammals based on skulls and dentaries,using identification keys (Bellocq and Kravetz 1983, Go-mez Villafane et al. 2005) and voucher specimens pre-served in the collection of Laboratorio de Vertebrados(Facultad de Ciencias Exactas y Naturales, Universidad Na-cional de Mar del Plata). Mammals were classified by age(offspring, juvenile, adult or old) based on voucher spec-imens, according to molar wear for cricetine rodents (Bel-locq and Kravetz 1983) and length of dental series formarsupials (Redford and Eisenberg 1992).

We expressed diet composition as the relative frequency(number of individuals of each prey item divided by thetotal number of prey, %F) and as the relative biomass(number of individuals of each prey item multiplied bythe corresponding mean body mass, and divided by thetotal biomass consumed, %B). Masses of prey items weretaken from our unpublished data or from literature (Red-ford and Eisenberg 1992, Gomez Villafane et al. 2005,Vargas et al. 2007).

We analyzed the mean size of prey, the food-nichebreadth, and the diet similarity among years (Marti et al.2007). Mean size of prey was estimated as the GeometricMean Weight of Prey (GMWP), which was discriminated byage for mammals. Food-niche breadth was calculated usingthe Levins’ Index: B 5 1/(Spi

2), where pi is the propor-tion of prey item i in the diet, and the Standardized Lev-ins’ Index: Bsta 5 (Bobs 2 Bmin)/(Bmax 2 Bmin), whereBmin 5 1 and Bmax 5 n; values range from 0 to 1 and allowcomparisons between samples with different numbers ofprey items. We examined diet similarity using the PiankaOverlap Index: O 5 Spijpik/(Spij

2pik2)1/2, where pij and

pik are the proportions of the prey item i in seasons j and k,respectively; values range from 0 (no prey item in com-mon) to 1 (identical proportional composition; Marti etal. 2007). We evaluated statistical differences in prey com-position among years using the Kendall’s Coefficient ofConcordance (W) and chi-square test (Zar 1984). Valuesof W range from 0 to 1, with higher values indicatinghigher similarity. Age composition of mammalian prey inthe diet was analyzed by means of G-test (Zar 1984). Valuesare expressed as mean 6 SD, followed by range in paren-theses.

RESULTS

We collected 228 pellets during the nonbreeding sea-sons for the complete sampling period (75 in 2006, 93 in2007 and 60 in 2008). Pellets were collected at six roostsites used by about 10 adult and juvenile Roadside Hawks.From these samples, we identified 482 prey, with an aver-age of 2.2 6 1.03 prey per pellet (range 5 1–6 prey items).Pellets averaged 34.1 6 5 mm (range 5 17.4–48.9 mm) inlength and 26.7 6 4.1 mm (range 5 14.5–36.8 mm) inwidth (n 5 185 pellets).

The diet of the Roadside Hawk consisted almost exclu-sively of small mammals (98.2%F), especially cricetine ro-dents (94.9%F; Table 1). In particular, the field mouse(Akodon azarae) accounted for .55% of the diet for allnonbreeding seasons (.63%B). Prey items such as insectsand amphibians were scarce in the diet of the RoadsideHawk and they were obtained from samples collected atthe beginning of the cold season, when these prey itemswere still available. The majority of small mammals foundin hawk’s diet (70.4%F) were species that typically inhabitgrasslands (i.e., A. azarae, long-nosed mouse [Oxymycterus

Table 1. Numeric (%F) and biomass (%B) contributionof each prey item for the complete sampling period(nonbreeding seasons 2006–08). Unidentified prey wereassigned masses of known prey species of similar size.

PREY ITEM

MASS TOTAL

(g) n %F %B

Mammals

Rodents

Akodon azarae 28.3 301 62.45 70.34Calomys spp. 17.4 105 21.78 13.17Oligoryzomys flavescens 26.5 28 5.81 6.86Oxymycterus rufus 77.7 4 0.83 1.63Holochilus brasiliensis 266.7 2 0.41 1.21Necromys obscurus 40 1 0.21 0.30Unidentified rodents 27.4 17 3.53 4.13

Marsupials

Monodelphis dimidiata 46.5 16 3.32 2.01

Birds

Unidentifiedpasserines

34 1 0.21 0.26

Amphibians

Hypsiboas pulchellus 6 1 0.21 0.05

Insects

Orthoptera 1 2 0.41 0.02Coleoptera 1 2 0.41 0.02Unidentified insects 1 2 0.41 0.02

Total 482

258 SHORT COMMUNICATIONS VOL. 45, NO. 3

rufus], dark bolo mouse [Necromys obscurus], and southernshort-tailed opposum [Monodelphis dimidiata]), a lower pro-portion (29.1%F) were species that inhabit agroecosystems(i.e., vesper mice [Calomys spp.], pampas rice rat [Oligoryz-omys flavescens]) and only one prey item was a typical wetlandspecies (0.004%F; i.e., marsh rat [Holochilus brasiliensis]).

The Roadside Hawk prey ranged in size from 1 g (in-sects) to 80 g (H. brasiliensis young). Fully 90% of preyrepresented in the pellets were small-sized rodents, suchas A. azarae, O. flavescens, and Calomys spp., all of whichweigh ,30 g (Table 1). The age composition of thesesmall rodents was significantly biased toward (a) large in-dividuals for A. azarae and O. flavescens (G 5 24.6, df 5 2, P, 0.001 and G 5 8.99, df 5 2, P 5 0.02, respectively) and(b) juveniles for Calomys spp. (G 5 22.12, df 5 2, P ,

0.001). In contrast, mammals with mass .30 g, such asM. dimidiata, O. rufus, and H. brasiliensis, were uncommon(,5%, Table 1) and were represented only by juveniles. Asa consequence of this dominance of small rodents in thediet, the GMWP was relatively low (25.2 g 6 0.48 SE).

The food-niche breadth indices were low for the com-plete sampling period (B 5 2.26, n 5 13, and Bsta 5 0.10),reflecting the dominance of a few prey items in the diet ofthe Roadside Hawk. The Standardized Levins’ Index (Bsta)showed little variation among years, varying from 0.15 in2006 to 0.17 in 2007 to 0.23 in 2008.

In addition, no differences in diet composition amongyears were observed (W 5 0.76; x2 5 27.47, df 5 12, P 5

0.007). Dietary overlap was greatest between 2006 and2007 (O 5 0.989), intermediate between 2007 and 2008(O 5 0.973), and least between 2006 and 2008 (O 5

0.944).

DISCUSSION

The Roadside Hawk diet during the nonbreeding seasonwas dominated by small mammals in the southeasternpampas of Argentina. In addition, there were no differenc-es among sampling years, indicating a consistent pattern inthe type of prey taken by this species during the nonbreed-ing season. Our work agreed in part with results reportedby Panasci and Whitacre (2000) during breeding season inGuatemala, where this hawk also consumed many smallvertebrates. However, our results differed from those of aprevious study in Argentina, which included both seasonsand characterized this species as mainly insectivorous(Beltzer 1990).

Such differences between studies may be due to thedifferent methodological approaches employed, as smallor soft-bodied prey such as amphibians and insects maybe underrepresented in pellet analyses (Marti et al.2007). However, such differences may also result from dif-ferences in sampling seasons and areas. The diet of gener-alist raptors usually varies spatially and seasonally, accord-ing to prey availability (Thiollay 1994). This opportunisticforaging mode has been reported for several Buteos, whichgenerally select the prey that is most locally abundant preyor easiest to catch (e.g., Errington and Breckenridge 1938,

Steenhof and Kochert 1985, Jedrzejewski et al. 1994, Figue-roa Rojas et al. 2003, Sarasola and Negro 2005, Trejo et al.2006, Bechard et al. 2010). In our study, the dominance ofsmall mammals in Roadside Hawk’s diet during the coldernonbreeding season (April–September) coincides with theperiod when the abundance of rodents increases due tothe recruitment period in the study area (Malizia et al.2001). Thus, we do not dismiss the possibility that theRoadside Hawk has a more diverse diet during the warmerbreeding season (October-March), when rodent preyabundance declines and other prey, including amphibiansand invertebrates, are more available.

The small mammal species consumed by Roadside Hawksin our study are typical of the environments which surroundthe tala forest (Malizia et al. 2001). Although this raptorseems to hunt in a variety of habitats, it is likely that grass-lands and edges are its preferred foraging habitats withinour study area, given the dominance in its diet of A. azarae,one of the most abundant rodents in grasslands and edges,and the presence of M. dimidiata, a species that is almostendemic to pampean grassland (Redford and Eisenberg1992, Massoia et al. 2000, Gomez Villafane 2005). However,the presence of rodents typically associated with agroecosys-tems (Calomys spp. and O. flavescens) and wetlands (H. bra-siliensis; Gomez Villafane 2005) suggests some degree ofopportunism in the hunting habits of this hawk.

We noted that Roadside Hawks consumed mainly juve-nile individuals of larger mammals, but preyed on all ageclasses of the small-sized mammal species. Although thesample size for large prey was small, our study suggestedthat there may be a maximum prey size Roadside Hawkscan use, about 80 g, the size of young H. brasiliensis. Inaddition, the mean prey weight for the Roadside Hawk(25 g) corresponded with the mean size of the most abun-dant cricetine rodents in the study area (Malizia et al.2001). These findings agreed with those of Panasci andWhitacre (2000), who reported that this raptor speciespreyed mainly on small-sized vertebrate prey.

In our study area, this raptor species has experienced apopulation increase in recent years, as it was consideredrare a few years ago (Martınez 2001) and now it seems tobe a common species (A. Baladron unpubl. data). Addi-tional studies of the Roadside Hawk’s breeding-season dietthroughout its entire geographical range are needed toelucidate the latitudinal and seasonal patterns of prey con-sumption of this predator.

HABITOS TROFICOS DE BUTEO MAGNIROSTRIS DU-RANTE EL PERIODO NO REPRODUCTIVO EN EL SUD-ESTE DE LA REGION PAMPEANA DE ARGENTINA

RESUMEN.—Se estudiaron los habitos troficos de Buteomagnirostris durante los periodos no reproductivos entre2006–08 en el sudeste de la region pampeana de Argen-tina. Colectamos 228 egagropilas en seis sitios de descansoutilizados por adultos y juveniles (aproximadamente 10individuos), e identificamos sus contenidos hasta el nivel

SEPTEMBER 2011 SHORT COMMUNICATIONS 259

taxonomico mas bajo posible. B. magnirostris se alimentoprincipalmente de pequenos mamıferos (98.2%), especial-mente de roedores (94.9%). Items presa tales como aves,anfibios e insectos fueron encontrados en bajas propor-ciones en su dieta. Debido a que el raton de campo (Ako-don azarae) fue la presa mas importante tanto en numero(62.5%) como en biomasa (70.3%), (a) la amplitud denicho trofico presento valores bajos (Indice de LevinsEstandarizado 5 0.10) y (b) el tamano promedio de presastambien fue relativamente bajo (25.2 g). La composicionde la dieta fue similar para todos los periodos de muestreo(Coeficiente de Concordancia de Kendall 5 0.76; x2 5

27.47, gl 5 12, P 5 0.007), mostrando altos valores desolapamiento entre anos (Indice de Pianka .94%). Nues-tros resultados concordaron con los reportes previos queindicaban que B. magnirostris consume pequenos vertebra-dos en Sudamerica, y evidenciaron tambien que la dieta deesta rapaz es mas amplia de lo que se habıa reportadopreviamente para Argentina, donde era considerada comouna especie principalmente insectıvora.

[Traduccion del equipo editorial]

ACKNOWLEDGMENTS

We thank P. Urrutia and his family for their courtesy andpermission to work on his ranch. Our work was supportedby Universidad Nacional de Mar del Plata Fund to Labor-atorio de Vertebrados (15/E317), and a Conicet Scholar-ship to A. Baladron. Equipment for this research was pro-vided through an Idea Wild Grant to A. Baladron. We alsothank two anonymous reviewers for their interesting andconstructive comments on an earlier draft of this manu-script.

LITERATURE CITED

BECHARD, M.J., C.S. HOUSTON, J.H. SARASOLA, AND A.S.ENGLAND. 2010. Swainson’s Hawk (Buteo swainsoni). InA. Poole [ED.], The birds of North America online.Cornell Laboratory of Ornithology, Ithaca, NY U.S.A,http://bna.birds.cornell.edu/bna/species/265 (lastaccessed 26 September 2010).

BELLOCQ, M.I. AND F. KRAVETZ. 1983. Identificacion deespecies, sexo, y edad relativa a partir de restos oseosde roedores de la provincia de Buenos Aires, Argen-tina. Historia Natural 3:101–112.

BELTZER, A.H. 1990. Biologıa alimentaria del Gavilan Co-mun Buteo magnirostris saturatus (Aves: Accipitridae) enel valle aluvial del Rıo Parana Medio, Argentina. Orni-tologia Neotropical 1:3–8.

BIERREGAARD, R.O., JR. 1998. Conservation status of birds ofprey in the South American tropics. Journal of RaptorResearch 32:19–27.

BILENCA, D. AND F. MINARRO. 2004. Identificacion de areasvaliosas de pastizal en las pampas y campos de Argen-tina, Uruguay y Sur de Brasil. Fundacion Vida SilvestreArgentina, Buenos Aires, Argentina.

BO, M.S., A.V. BALADRON, AND L.M. BIONDI. 2007. Ecologıatrofica de Falconiformes y Estrigiformes: tiempo desıntesis. Hornero 22:97–115.

CABRERA, A.L. 1971. Fitogeografıa de la Republica Argen-tina. Boletın de la Sociedad Argentina de Botanica 19:1–42.

CANEVARI, M., P. CANEVARI, R. CARRIZO, G. HARRIS, J. RODRI-

GUEZ MATA, AND R.J. STRANECK. 1991. Nueva guıa de lasaves argentinas. Fundacion Acindar, Buenos Aires, Ar-gentina.

DEL HOYO, J., A. ELLIOTT, AND J. SARGATAL. 1994. Handbookof the birds of the world, Vol 2. New World vultures toguineafowl. Lynx Editions, Barcelona, Spain.

ERRINGTON, P.L. AND W.J. BRECKENRIDGE. 1938. Food habitsof Buteo hawks in north-central United States. WilsonBulletin 50:113–121.

FIGUEROA ROJAS, R.A., E.S. CORALES STAPPUNG, AND O.S.ALVARADO. 2003. Diet of the Red-backed Hawk (Buteopolyosoma) in a forested area of the Chilean Patagoniaand its relation to the abundance of rodent prey. Hor-nero 18:43–52.

GOMEZ VILLAFANE, I.E., M. MINO, R. CAVIA, K. HODARA, P.COURTALON, O. SUAREZ, AND M. BUSCH. 2005. Guıa deroedores de la Provincia de Buenos Aires. L.O.L.A. (Lit-erature of Latin America), Buenos Aires, Argentina.

HAVERSCHMIDT, F. 1962. Notes on the feeding habits andfood of some hawks of Surinam. Condor 64:154–158.

ISACCH, J.P., M.S. BO, AND M.M. MARTINEZ. 2000. Food hab-its of the Striped Owl (Asio clamator) in Buenos Airesprovince, Argentina. Journal of Raptor Research 34:235–237.

JEDRZEJEWSKI, W., A. SZYMURA, AND B. JEDREZEJEWSKA. 1994.Reproduction and food of the buzzard Buteo buteo inrelation to the abundance of rodents and birds in Bia-lowieza National Park, Poland. Ethology, Ecology and Evo-lution 6:179–190.

MALIZIA, A.I., D. ANTINUCHI, AND A.I. VASSALLO. 2001. As-pectos ecologicos de la comunidad de roedores de laReserva de Mar Chiquita con enfasis en el roedor sub-terraneo Ctenomys talarum. Pages 287–302 in O. Iri-barne [ED.], Reserva de Biosfera Mar Chiquita: carac-terısticas fısicas, biologicas y ecologicas. UNESCO-Editorial Martin, Mar del Plata, Argentina.

MARTI, C.D., M.J. BECHARD, AND F.M. JAKSIC. 2007. Foodhabits. Pages 129–151 in D.M. Bird and K.L. Bildstein[EDS.], Raptor research and management techniques.Hancock House, WA U.S.A.

MARTINEZ, M.M. 2001. Avifauna de Mar Chiquita: sıntesisde la tesis doctoral de M.M. Martınez. Pages 227–250 inO. Iribarne [ED.], Reserva de Biosfera Mar Chiquita:caracterısticas fısicas, biologicas y ecologicas. UN-ESCO-Editorial Martin, Mar del Plata, Argentina.

MASSOIA, E. 1988. Presas de Buteo magnirostris en el partidode General Rodrıguez, provincia de Buenos Aires.APRONA Boletın Cientıfico 10:8–11.

———, A. FORASIEPI, AND P. TETA. 2000. Los marsupialesde la Argentina. L.O.L.A. (Literature of Latin Amer-ica), Buenos Aires, Argentina.

MAZAR-BARNETT, J. AND M. PEARMAN. 2001. Annotatedchecklist of the birds of Argentina. Lynx Edicions, Bar-celona, Spain.

260 SHORT COMMUNICATIONS VOL. 45, NO. 3

NAROSKY, T. AND A. DI GIACOMO. 1993. Las aves de la pro-vincia de Buenos Aires: distribucion y estatus. Asocia-cion Ornitologica del Plata, Vazquez Massini andL.O.L.A. (Literature of Latin America), Buenos Aires,Argentina.

PANASCI, T. AND D. WHITACRE. 2000. Diet and foraging be-havior of nesting Roadside Hawks in Peten, Guatemala.Wilson Bulletin 112:555–558.

REDFORD, K.H. AND J.F. EISENBERG. 1992. Mammals of theneotropics: the southern cone, Vol. 2. The University ofChicago Press, Chicago, IL U.S.A.

SARASOLA, J.H. AND J.J. NEGRO. 2005. Hunting success ofwintering Swainson’s Hawks: environmental effects ontiming and choice of foraging method. Canadian Jour-nal of Zoology 83:1353–1359.

STEENHOF, K. AND M.N. KOCHERT. 1985. Dietary shifts ofsympatric Buteos during a prey decline. Oecologia66:6–16.

STUTZ, S. 2001. Vegetacion del area de la Laguna MarChiquita. Pages 75–78 in O. Iribarne [ED.], Reservade Biosfera Mar Chiquita: caracterısticas fısicas, biolo-gicas y ecologicas. UNESCO-Editorial Martin, Mar delPlata, Argentina.

THIOLLAY, J.M. 1994. Family Accipitridae (hawks and eagles).Pages 52–205 in J. del Hoyo, A. Elliott, and J. Sargatal

[EDS.], Handbook of birds of the world, Vol. 2. New Worldvultures to guineafowl. Lynx Editions, Barcelona, Spain.

TORRES ROBLES, S.S. AND N.M. TUR. 2006. Los talares de laProvincia de Buenos Aires. Pages 246–250 in A.D.Brown, U. Martinez-Ortiz, M. Acerbi, and J. Corcuera[EDS.], Situacion ambiental Argentina 2005. FundacionVida Silvestre, Buenos Aires, Argentina.

TREJO, A., V. OJEDA, M. KUN, AND S. SEIJAS. 2006. Prey ofWhite-throated Hawks (Buteo albigula) in the southerntemperate forest of Argentina. Journal of Field Ornithol-ogy 77:53–57.

VARGAS, R.J., M.S. BO, AND M. FAVERO. 2007. Diet of theSouthern Caracara (Caracara plancus) in Mar ChiquitaReserve, southern Argentina. Journal of Raptor Research41:113–121.

VIGLIZZO, E.F., F.C. FRANK, AND L. CARRENO. 2006. Situacionambiental en las ecorregiones Pampa y Campos y Malezales.Pages 263–273 in A.D. Brown, U. Martinez-Ortiz, M. Acerbi,andJ. Corcuera [EDS.], Situacionambiental Argentina 2005.Fundacion Vida Silvestre, Buenos Aires, Argentina.

ZAR, J.H. 1984. Biostatistical analysis. Prentice Hall, Engle-wood Cliffs, NJ U.S.A.

Received 24 November 2010; accepted 25 April 2011Associate Editor: Vincenzo Penteriani

SEPTEMBER 2011 SHORT COMMUNICATIONS 261