DECEMBER 1994 SHORT COMMUNICATIONS 265

COLLOPY,M.W. AND K.L. BILDSTEIN. 1987. Foraging relation to prey biomassand habitat structure.Condor behaviorof northernharriers wintering in southeastern 92:107-112. salt and freshwater marshes. Auk 104:11-16. PYLYPE½,B. 1991. Impacts of fire on bird populations CONOVER,W.J. 1980. Practical nonparametricstatistics. in a fescueprairie. Can. Field-Nat. 105:346-349. 2nd ed. John Wiley, New York, NY U.S.A. RUDOLPH,S.G. 1982. Foraging strategiesof American HAMERSTROM,F.N. 1974. Raptor Management. Pages kestrelsduring breeding.Ecology 63:1268-1276. 5-8 in F.N. Hamerstrom, B.E. Harrell, and R.R. SCHIPPER,W.J.A., L.S. BURMA AND P. BOSSENBROEK. Olendorff [EDS.],Management of raptors. Raptor Res. 1975. Comparative study of hunting behaviorof win- Rep. 2. tering hen harriers (Circuscyaneus ) and marshharriers (Circusaeruginosus). Ardea 63:1-29. JtaqES,S.W. 1985. Habitat selectionin raptorial birds. SMALLWOOD,J.A. 1987. Sexual segregationby habitat Pages159-188 in M.L. Cody [ED.], Habitat selection in Americankestrels wintering in southcentralFlorida: in birds. Academic Press, New York, NY U.S.A. vegetativestructure and responsesto differential prey LUDWIG, J.A., AND J.F. REYNOLDS. 1988. Statistical availability. Condor89:842-849. ecology.Wiley and SonsInc., New York, NY U.S.A. , M. WOODRE¾,M.J. SMALLWOODAND M.A. MILLSAP,B.A., K.W. CLINE ANDB.A. GIRON PENDLETON. KETTLER. 1982. Foraging by cattle egretsand Amer- 1987. Habitat Management. Pages215-237 in B.A. ican kestrelsat a fire's edge.]. Field Ornithol.53:171- Giron Pendleton,B.A. Millsap, K.W. Cline, and D.M. 172. Bird lEDs.I, Raptor managementtechniques manual. TOLAND,B.R. 1987. The effect of vegetativecover on Natl. Wildl. Fed., Washington,DC U.S.A. foraging strategies,hunting success,and nesting dis- PETERSON,K.L. AND LB. BEST. 1987. Effects of pre- tribution of American kestrelsin central Missouri. J. scribedburning on nongamebirds in a sagebrushcom- Raptor Res. 21:14-20. munity. Wildl. Soc.Bull. 15:317-329. PRESTON,C.R. 1990. Distribution of raptor foraging in Received24 January 1994; accepted6 August 1994

]. Raptor Res. 28(4):265-268 ¸ 1994 The Raptor ResearchFoundation, Inc.

WINTER DIET or LONG-EAREDOWLS (AsIO OTUS) IN THE PO PLAIN (NORTHERN ITALY)

PAOLO GALEOTTI AND LUCA CANOVA Dipartimentodi BiologiaAnitaale Universitddi Pavia - Piazza Botta 9, 27100 Pavia, Italy

KEY WORDS: foodhabits; diet; Italy; long-earedowl; Asio part of their Italian wintering and breedingrange (Ga- otus. leotti 1990). In this paper, we review the diet of long-earedowls in The winter diet of the long-earedowl (Asiootus) has the Po Plain to: (1) providenew information on the trophm beenwell documentedin northernand centralEurope and nicheof southernwintering populations of long-earedowls, North America (see Cramp 1985 for review), but there (2) comparelocal diets, and (3) determinethe hunting are few data for southernEurope and particularly Italy. habitatsmost utilized by the species. In northern Europe, the long-eared owl specializesin STUDY AREAS AND METHODS hunting voles( spp.) in open fields (Herrera and Hiraldo 1976), and it is considered a restricted feeder This area has a sublittoralcontinental temperate climate (Marti 1976, K511ander1977, Nilsson 1981). Likewise, with two peaksof rainfall in spring and autumn; during •n the Mediterranean regionvoles are the mostimportant winter the mean temperature ranges from 0-10øC and precipitationaverages 50-60 mm monthly. componentin the diet of long-earedowls (Araujo et al. Pelletswere collectedbetween January and March from 1973, Tome 1991). Only three studies(Gerdol and Perco eight winter roosts located in the Po Plain. Roosts 1, 2, 1977, Casini and Magnaghi 1988, Canova 1989) have and 3 (Table 1) were closeto the easternedge of the study reportedthe diet and prey selectionof long-earedowls in area, a few kilometers from the Adriatic Sea, while all the Po Plain of northernItaly, which is the mostimportant other roostswere locatedin Lombardy, the central part 266 SHORT COMMUNICATIONS VOL. 28, NO. 4 DECEMBER 1994 SHORT COMMUNICATIONS 267 of the Po Plain. Roostswere between25-450 km apart. rare prey in the diets. The frequencyof farmland species The habitattypes surrounding each roost (2.5 km radius) in the diet (Rattusrattus, Apodemus agrarius, and Microtus are reported in Table 1. arvalis) increasedtoward the east,while woodlandspecies Although the long time span over which pellets were (Clethrionomysglareolus, and Microtus multiplex) were collected(16 yr) couldbe responsiblefor variation in local preyedon more often at westernsites. This was consistent diets, we found no evidenceof fluctuations in small with the localized distribution of Clethrionomysglareolus populationsin northern Italy among years (L. Canova which is locally abundantin woodedhabitats in the west- unpubl. data). Moreover, there is evidencethat somevole ern portion of the Po Plain, but scatteredor absentin the speciesliving in Mediterraneanregions are notcyclic (Par- East (Canova et al. 1991). Hygrophilousspecies were also adis and Guedon 1993). Finally, the diet of long-eared mainly exploitedin westernlocations (roosts 4, 6, and 8), owls can be more variable between seasons than between where numerous ditches and canals were associated with years (Nilsson 1981). Therefore, we believethat, taken rice fields. together,these findings justify our tentativecomparison CONCLUSIONS amonglocal diets irrespective of the yearsin which pellets were collected. The diet of wintering long-eared owls in the Po Plain All pellets were examined using standardtechniques consistedmainly of mice, whereas elsewherein Europe (Yalden 1977). Prey remainswere identifiedusing taxo- long-earedowls prey mainly on voles (Saint Girons and nomic keys (Erome and Aulagnier 1982), and reference Martin 1973, Araujo et al. 1973, Glue and Hammond specimenscollected in the study areas.Because few work- 1974, Marti 1976, K•illander 1977, Tome 1991). This ers have identified birds to speciesin dietary studieswe differencewas probably due to both a lower richnessin consideredthem as a singlecategory. Because they were vole species(only eight of the 20 European Microtidae all smallpasserines (mainly Passerspp.), we useda mean speciesoccur in Italy) and low populationlevels in south- mass of 20 g for biomass calculations. Small ern Europe comparedto the North (Herrera and Hiraldo biomass was derived from the literature (Di Palma and 1976). Moreover, the number of vole speciesdecreases Massa 1981, Galeotti et al. 1991). Frequencyby number acrossthe Po Plain from eastto west,with only four species and biomassfor each prey speciesand the mean massof beingpresent in the west (Niethammer and Krapp 1982). prey were calculatedfor diets at each roost. Voles are scarcer than mice in most habitats except in Diet breadth (basedon frequenciesof ecologicalprey- scrubs and woods (Canova and Fasola 1991, P. Galeottl categories)was determinedby the index:B = 1/R 2;p,2 and L. Canova unpubl. data). The apparently close re- (Feinsingeret al. 1981) where p is the proportionof the lationship betweendiet compositionand prey availability prey i in the total sample and R is the number of prey confirmsthe trophic plasticityof long-earedowls in their categoriescollected at eachstation; the B-index variesfrom Italian winter range (Canova 1989). 0 (no useof any resource)to 1 (full useof total resources). RESUMEN.--La dieta de Asio otus invernantes fue estu- RESULTS AND DISCUSSION diada en Po Plain al norte de Italia, a travgs de anfilisis Overall Diet. We identified 3499 prey items that de egaõrfipilasobtenidas desde ocho perchas de descanso amountedto a total biomassof 75 466 g. Prey included invernal. En contrastecon lo que ocurre en el norte y (89.6%), birds (10.2%) and insects(0.2%). Al- centro de Europa, los ratonespredominaron por sobrelas though long-earedowls preyed on 16 mammal species ratas de aqua. La composici6ndietaria sugirio que las from four families, three species(Apodernus sylvaticus, Mi- tierras de cultivo eran los hfibitat de alimentaci6npreva- crotussavii, and Microraysminutus) accountedfor 64.8% lecientesalrededor de las perchas.La variaci6n dieteria of the diet and murid rodentspredominated overall (Table desdepresas de mamiferos a aves puede ocurrir en con- 1) The mean massof prey (21.5 g) was lower than that dicionesclimfiticas adversas (nieves otofiales) o en hfibitat calculated(32.2 g) by Marti (1976) from a number of urbanos. Europeanstudies; consequently, the averagemeal was also [Traducci6n de Ivan Lazo] slightlylower (51.8 g) than that reportedfrom a number of diets in northern Europe and North America (55-60 g) ACKNOWLEDGMENTS Local Diets and Feeding Habitats. Diets differedin We wish to thank D.A. Kirk and J.S. Marks for their type and proportionof mammal prey species.Murids were the most important prey categoryat all but two roosts. useful suggestionsand criticismon earlier drafts of the Microtids were the secondmost common prey used by paper, and M.T. Forlini for her help in pellet analysis. long-earedowls at all roostsbut one,and theywere preyed on more heavily at easternsites. Birds were preyed on at LITERATURE CITED all roosts,but predominatedin the diet of long-earedowls ARAuJo,J., J.M. REY,A. LANDINAND A. MORENO. 1973 in the urban roostand in willow/farmland. The impor- Contribucion al estudio del buho chico (Asio otus) en tance of birds in owl's diet at one roost was related to weather:the frequencyof bird prey increasedin relation Espafia. Ardeola19:397-428. to the snow cover, ranging from 13-14% when snow was CANOVA,L. 1989. Influence of snow cover on prey se- absentto 42% when snow coveredthe ground (Canova lectionby long-earedowls Asiootus. Ethol. Ecol. Evol. 1989). Niche breadth increased in relation to an increase 1:367-372. •n woodland species(r• = 0.92, P (0.01) which were -- AND M. FASOLA. 1991. Communities of small 268 SHORT COMMUNICATIONS VOL. 28, NO. 4

mammalsin six biotopesof northernItaly. ActaTheriol. of the long-earedowl in Britain and Ireland. Dr. Birds 36:76-86. 67:361-369. --, P. GALEOTTI AND m. FASOLA. 1991. Distri- HERRERA, C.M. AND F. HIRALDO. 1976. Food-niche bution of the bank vole Clethrionornysglareolus in plain and trophic relationshipsamong European owls. Orms habitatsof northern Italy. Mammalia 55:435-439. Scan& 7:29-41. CASINI, L. AND A. MAGN^GHI. 1988. Alimentazione in- KKLLANDER,H. 1977. Food of the long-earedowls Aszo vernale di gufo comuneAsio otus in un'area agricola otus in Sweden. Ornis Fenn. 54:79-84. dell'Emilia orientale. Avocetta 12:101-106. MARTI, C.D. 1976. A review of prey selectionby the CRAMP,S.C. 1985. The birds of the western Palearctic. long-earedowl. Condor78:331-336. Vol. V. Oxford Univ. Press, Oxford, U.K. NIETHAMMER,J. AND F. KRAPP. 1982. Handbuch der OI PALMA, M.G. AND B. MASSA. 1981. Contributo me- Saugetiere Europas. Rodentia. Akad. Verlag, Wies- todologicoper lo studiodell'alimentazione dei rapaci. baden,Germany. Atti Cony. Ital. Orni. 1:69-76. NILSSON,I.N. 1981. Seasonalchanges in food of the EROME,G. AND S. AULAGNIER. 1982. Contribution /t Iong-eared owl in southern Sweden. Ornis Scan& 12' l'identificationdes proiesdes Rapaces.Bievre 2:129- 216-223. 135. PARADIS,E. AND G. GUEDON. 1993. Demographyof a FEINSINGER,P., E.E. SPERSAND R.W. POOLE. 1981. A Mediterranean microtine:the Mediterranean pine vole, simplemeasure of nichebreadth. Ecology 62:27-32. Microtusduodecimcostatus. Oecologia 95:47-53. GALEOTTI, P. 1990. Gufo comune Asio otus. Page 107 SAINTGIRONS, M.C. ANDC. MARTIN. 1973. Adaptation in P. Brichetti and M. Fasola [EDS.], Atlante degli du r•gime de quelquesrapaces nocturnes au paysage Uccelli nidificanti in Lombardia, Editoriale Ramperto, rural. Les proiesde l'Effraie et du Moyen-duc dansle Brescia, Italy. department de la Somme. Bull. Ecol. 4:95-120. --, F. MORIMANDOAND C. VIOLANI. 1991. Feeding TOME, D. 1991. Diet of the long-earedowl Asiootus in ecologyof the tawnyowl (Strixaluco) in urbanhabitats Yugoslavia. Ornis Fenn. 68:114-122. (northern Italy). Boll. Zool. 58:143-150. YALDEN, D.W. 1977. The identification of remains in GERDOL, R. AND F. PERGO. 1977. Osservazioni ecolo- owl pellets.Occas. Publ. Mammal. Soc.,London, U.K. giche sul gufo comune(Asio otus otus L.) nell'Italia Nord-Orientale. Boll. Soc. Adriat. Sci. 61:37-59. GLUE,D.E. ANDG.J. HAMMOND. 1974. Feedingecology Received21 April 1993; accepted29 April 1994

J. Raptor Res. 28(4):268-273 ¸ 1994 The Raptor ResearchFoundation, Inc.

REFINEMENTSTO SELECTIVETRAPPING TECHNIQUES: A RADIO-CONTROLLED BOW NET AND POWER SNARE FOR BALD AND GOLDEN EAGLES

RONALDE. JACKMAN,W. GRAINGERHUNT, DANIELE. DRISCOLLAND FRANKJ. LAPSANSKY BioSystemsAnalysis, Inc., 303 PotreroStreet Suite 29-203, SantaCruz, CA 95060 U.S.A.

KEY WORDS: Aquila chrysaetos;bald eagle; bow net; cap- with Americankestrels (Falco sparverius). The powersnare, ture techniques;golden eagle; Haliaeetus leucocephalus; a "manually-operated,single noosesystem," was devel- power snare. oped for the selectivecapture of white-bellied sea-eagles (Haliaeetusleucogaster) by Hertog (1987). Researchand managementof raptorsoften requiresthe During studiesof wintering and breedingbald eagles capture of specificindividuals for radiotaggingor color- (Haliaeetusleucocephalus) and goldeneagles (Aquila chry- marking. Bloom (1987) reviewed raptor trapping tech- saetos)in Washington,California, and Arizona (Hunt et niques,including several selective methods used for eagles: al. 1992a, 1992b, 1992c, 1992d), we constructeda radio- cannonand rocketnets (see also Grubb 1988), the pit trap, controlledbow net to selectivelycapture eagles (Fig. l a). and our bow net. Meng (1963) wasfirst to developa radio- We were able to completelyconceal it in loosesoil and controlledbow net and Bryan (1988) modified it for use operate it from distancesup to 400 m. In addition, we