SHORT COMMUNICATION j. Raptor Res. 27(4):214-216 ¸ 1993 The Raptor ResearchFoundation, Inc.

FOOD HABITS OF THE RUFOUS-LEGGEDOWL (STRIX RUFIPES)IN TEMPERATE RAINFORESTS OF SOUTHERN

DAVID R. MARTINEZ Laboratoriode Ecologfa,Departamento de CienciasBdsicas. Universidad de LosLagos, Casilla 933, Osorno,Chile

The Rufous-leggedOwl (Strixrufipes) is the leastknown hair or feathers of a given specieswere deemedas rep- owl speciesinhabiting the temperaterainforest region of resentingonly one individual). For insectidentification, I southernSouth America. The scarcebiological knowledge followed Pefia (1986) and quantified theseprey by count- aboutthis speciesis either anecdotal(Housse 1945, John- ing head capsulesand mandibles.I identified prey items to the finest possibletaxonomic category. son 1967) or consistsof brief accountson taxonomyand The mass of most prey was determined by weighing distribution(e.g., Humphrey et al. 1970,Vuilleumier 1985, individuals captured at the study area. Some mass esti- Jaksifiand Feinsinger1991). There is no publishedin- mateswere taken from the literature (Pearson1983, Jaksifi formation on the diet of Rufous-leggedOwls. Here, I et al. 1986). I estimated the biomass contribution of each report the first quantitative data on the food habits and prey type to the owls' diet by multiplying the number of prey selectionby these owls. individualsin the pellets by the mean body massof that item. I assumedthat massesof unidentified prey were STUDY AREA AND METHODS similar to the average mass of the most closelyrelated I studiedRufous-legged Owls at two siteslocated in the identified taxa. Valdivian Rain Forest Region of Southern Chile (sensu Becausethere were no important differencesin the con- Veblen et al. 1983). One was San Martin Experimental tents of pellets collectedat both sites, I pooled these data Forest (39038'S, 73007'W; 20 m elevation), located on the and analyzedthe combineddiet on a seasonaland year- coastalranges of Valdivia . This 80 ha area was round basis. coveredby multilayered forestsdominated by Aextoxicum RESULTS AND DISCUSSION punctatumand Podocarpussaligna with substantialpres- ence of Gevuina avellana and some scattered old individuals The 78 whole pelletsaveraged 35.4 + 0.86 mm x 21.8 of emergentNothofagus dombeyi. The understorywas sparse, +_0.55 mm and had a mean dry massof 2.8 +_0.36 g (• and the soil was coveredwith a thick layer of mossesand +_ SE). litter. The other site was a 25 ha second-growthforest The 161 pelletsanalyzed yielded 376 prey items(Table surroundingthe experimentalfish hatcheryat Lake Ru- 1), of which small mammalswere the mostfrequent. The panco(40039'S, 72038'W; 150 m elevation).This site was arboreal mouse(Irenomys tarsalis) was the most common contiguous with dense riparian forests running toward item in the diet in all seasons other than summer. The pre-Andean forestseast of Osorno Province. It was an long-tailed mouse (Oryzomyslonœicaudatus) was consis- almostpure standof old Aextoxicumpunctatum, with minor tently preyed upon year-round, and was the staple food amounts of Laurelia sempervirens,Gevuina aveliana, and of owls during spring and summerboth by number and Nothofagusdombeyi trees. It had a sparseshrub under- biomass.The colocoloopossum (Dromiciops australis) was growth of Chusqueaquila and a thin layer of mossesand betterrepresented during springand summerthan during litter. autumn and winter. Other mammalian prey includedthe Owl pairs remainedin both areasyear-round, and their introducedblack rat (Rattusrattus), the long-hairedmouse pelletswere collected under roosting trees. At SanMartin, (Akodonlongipilis), the olivaceusfield mouse(Akodon oh- I collected78 pellets from April (early autumn) 1988 to vaceus),the austral greater mouse(Auliscomys micropus), February (late summer) 1990, and in January 1992. At Darwin's leaf-eared mouse (Phyllotisdarwini) and an un- Rupanco, I collected83 pellets from February 1992 to identifiedbat, probablya big-earedbat (Histlotusmontan- January 1993. From the whole sample (161 pellets), I US). measuredand weighed78 intact pellets.I identifiedand Birds from the family Furnariidae mademinor contri- quantified most vertebratesin the pellets on the basis of butions in biomass. At least two of the unidentified Fur- skulls (Reise 1973) or dentary pairs (whichevergave the nariidae were probablyWhite-throated Treerunners (Py- highestcount). For other remains, suchas hairs and feath- garrhychasalbogularis ). ers, I usedreference collections and quantified theseprey The contribution of amphibians to total biomasscon- assumingthe smallestpossible number of individuals(e.g., sumed was negligible, and the remains observed(long

214 DECEMBER 1993 SHORT COMMUNICATION 215

Table 1. Foodhabits of the Rufous-leggedOwl (Strixrufipes) in primary growthtemperate rainforests of southern Chile. B% is percentby biomassand N is prey number.Mass a of prey itemsin grams.

MASS SUMMER AUTUMN WINTER SPRING TOTAL PREY (g) B% (N) B% (N) B% (N) B% (N) B% (N)

Mammals Akodonlongipilis 41 0.0 (0) 2.8 (2) 0.0 (0) 0.0 (0) 1.4 (2) Akodonolivaceus 23 0.0 (0) 0.0 (0) 4.1 (3) 3.0 (1) 1.5 (4) Auliscomysmicropus 58 0.0 (0) 1.9 (1) 0.0 (0) 0.0 (0) 1.0 (1) Irenomystarsalis 42 0.0 (0) 55.4 (39) 37.6 (15) 10.8(2) 39.2 (56) Oryzomyslongicaudatus 26 35.6 (8) 13.2(15) 31.0 (20) 33.4 (10) 23.0 (53) Phyllotisdarwini 66 0.0 (0) 4.4 (2) 0.0 (0) 0.0 (0) 2.2 (2) Rattusrattus 40b 13.7 (2) 1.3 (1) 2.4 (1) 5.1 (1) 3.3 (5) Unident. rodents 42.2 14.4 (2) 11.4 (8) 17.6 (7) 5.4 (1) 12.7 (18) Dromiciopsaustralis 34 23.3 (4) 6.9 (6) 4.1 (2) 26.2 (6) 10.2 (18) Unident. bat 15 0.0 (0) 0.0 (0) 0.0 (0) 1.9 (1) 0.2 (1) Subtotalmammals 87.0 (16) 97.3 (74) 96.8 (48) 85.8 (22) 94.7 (160)

Birds Aphrasturaspinicauda 18 0.0 (0) 0.6 (1) 1.1 (1) 0.0 (0) 0.6 (2) Unident. Furnariidae 18 3.1 (1) 0.6 (1) 0.0 (0) 2.3 (1) 0.9 (3) Subtotalbirds 3.1 (1) 1.2 (2) 1.1 (1) 2.3 (1) 1.5 (5) Amphibians Leptodactylidae 10 1.7 (1) 0.0 (0) 0.5 (1) 1.3 (1) 0.5 (3) Subtotalamphibians 1.7 (1) 0.0 (0) 0.5 (1) 1.3 (1) 0.5 (3) Insects Carabidae 0.84 0.0 (0) 0.1 (1) 0.0 (0) 0.0 (0) 0.1 (1) Cerambycidae 1.04 1.2 (7) 0.1 (1) 0.1 (2) 0.4 (3) 0.2 (13) Curculionidae 0.22 0.0 (0) 0.0 (0) 0.1 (2) 0.0 (0) 0.1 (2) Lucanidae 2.04 1.1 (3) 0.2 (3) 0.1 (1) 0.5 (2) 0.3 (9) Scarabaeidae 0.48 1.6 (20) 0.1 (2) 0.0 (0) 3.2 (52) 0.6 (74) Silphidae 0.45 0.0 (0) 0.0 (0) 0.1 (1) 0.0 (0) 0.1 (1) Acrididae 0.69 0.2 (2) 0.0 (0) 0.1 (1) 0.7 (8) 0.1 (11) Stenopelmatidae 1.35 0.5 (1) 0.7 (15) 0.6 (7) 0.2 (1) 0.5 (24) Blattidae 1.12 3.6 (19) 0.3 (7) 0.5 (8) 5.6 (39) 1.3 (73) SubtotalInsects 8.2 (52) 1.5 (29) 1.6 (22) 10.6 (105) 3.3 (208) Total preyitems 70 105 72 129 376 Total biomass(g) 584.8 2954.7 1674.5 778.9 5992.8 Total pellets 23 55 45 38 161 Massesfor mammalswere obtained from Pearson(1983) for Irenornysand Auliscornys,from Jaksi6et al. (1986) for Phyllotis,and from D.R. Martinez(unpubl. data) for the remaining taxa. Masses for insects are the average of representativemembers of eachfamily collected at the studysites (D.R. Martinez unpubl.data). Juveniles. femora) could be of arboreal frogs (Hylorina sylvatica),a tumn and winter insectswere uncommonin the diet, likely scarceanuran that climbsup vegetationusing its opposable becauseonly Blattidaeand Stenopelmatidaewere available halluces. in low numbersduring theseseasons. Insectsoutnumbered mammals in the diet only during Basedon my data the Rufous-leggedOwl may be con- spring and summer, but their biomasscontribution was sidereda generalistfeeder, taking a variety of prey avail- unimportanton a year-roundbasis. Individuals of Blat- able within the restrictionsimposed by its hunting tactics tidae (cockroaches)as well as Scarabaeidae(beetles), were (it is a sit-and-wait predator), and by prey size and be- the mostfrequent items, followed by camelcrickets (Steno- havior. Nevertheless, the most frequent vertebrate prey pelmatidae)and grasshoppers(Acrididae). During au- were arboreal or scansorial small mammals. Terrestrial 216 SHORTCOMMUNICATION VOL. 27, No. 4

smallmammals, despite their similar or higher field abun- Fuego).Preliminary Smithsonian Manual, Univ. Kan- dance(Murfia and Gonzalez 1986), and higher number sas Mus. Nat. Hist., Lawrence, KS U.S.A. of speciespresent in temperate rainforests(Meserve and JAKSI•,F.M., J.L. YAI•EZAND J.R. RAU. 1986. Prey Jaksi• 1991), were poorly representedas food items of and trophic ecologyof Great Horned Owls in western Rufous-leggedOwls, both by numbersand biomass.This South America: an indication of latitudinal trends. apparent differential utilization of prey resourcesby Ru- fous-leggedOwls warrants further examination. Raptor Res. 20:113-116. -- ANDP. FEINSINGER.1991. Bird assemblagesin RESUMEN.--Estees el primer estudiocuantitativo de los temperateforests of North and South America: a com- habitosalimentarios del Conc6n(Strix rufipes),producto parison of diversity, dynamics,guild structure,and del analisisde 161 egagr6pilasrecolectadas en dos am- resource use. Rev. Chil. Hist. Nat. 64:491-510. bientesno intervenidosde bosquetemplado en el sur de JOHNSON,A.W. 1967. The birdsof Chile and adjacent Chile. La composici6nde la dieta fluctu6 estacionalmente regions of , Bolivia and Peru. Volume II. e incluy6 varias especiesde mamlferos,aves, anuros e Platt EstablecimientosGraffcos, Buenos Aires, Argen- insectos.Las presasmas comunesfueron micromamfferos tina. (roedotesy una especiede marsupial) e invertebrados (principalmenteBlattidae y Scarabaeidae).Sin embargo, MESERVE,P.L. ANDF.M. JAKSI•. 1991. Comparisons el aporte en biomasade los primeros fue muy superioral of terrestrialvertebrate assemblages in temperaterain- de los insectos. E1 consumo de invertebrados fue mas fre- forests of North and South America. Rev. Chil. Hist cuentedurante primavera y verano,mientras queen otofio Nat. 64:511-535. e invierno los Conconesdepredaron casi exclusivamente MUROAR. ANDL.A. GONZ,•LEZ.1986. Regulationof sobre micromam•feros. Los micromam•feros de habitos ar- numbersin two neotropicalrodent species in southern borlcolasy escansorialesfueron mas depredadosque los Chile. Rev. Chil. Hist. Nat. 59:193-200. dehabitos terrlcolas. Asl, losConcones parecen seleccionar PEARSON,O.P. 1983. Characteristics of a mammalian las presasque constituyensu dieta. fauna from forestsin Patagonia,southern Argentina. [Traducci6n Autor] J. Mammal. 64:476-492. PF,I•A, L.E. 1986. Introducci6n a los insectos de Chile ACKNOWLEDGMENTS Editorial Universitaria,Santiago, Chile. I thank SusanChaplin for sponsoringme as a member REISE,D. 1973. Clave para la determinaci6nde los of RRF. Eric D. Forsman kindly sent me some of his craneosde marsupialesy roedoreschilenos. Gayana invaluable articles and unpublishedpapers on Spotted (Zoolog(a)27:1-20. Owls (Strix occidentalis).Theodore J. Cohn sentme hard- VEBLEN,T.T., F.M. SCHLEGELAND J.V. OLTREMARI to-retrievereports on owls, and his authoritativedescrip- 1983. Temperate broad-leavedevergreen forests of tions of SouthAmerican cricketshelped me identify those SouthAmerica. Pages5-31 in J.D. Ovington[ED.], prey. This work was fundedby FONDECYT 92-327 and DI-IPO 304-75. Temperatebroad-leaved evergreen forests. Elsevier Sci. Publ., Amsterdam, The Netherlands.

LITERATURE CITED VUILLEUMIER,F. 1985. Forestbirds of Patagonia:eco- logical geography,speciation, endemism, and faunal HOUSSE,R. 1945. Las aves de Chile en su clasificaci6n history.Pages 255-304 in P.A. Buckley,M.S. Foster, moderna:su vida y suscostumbres. Ediciones Univ. de E.S. Morton, R.S. Ridgely and F.G. Buckley[EDs.], Chile, Santiago, Chile. Neotropicalornithology. Ornithol. Monogr. 36. HUMPHREY, P.S., D. BRIDGE, P.W. REYNOLDSAND R.T. PETERSON. 1970. Birds of Isla Grande (Tierra del Received25 April 1993; accepted20 August1993