SHORT COMMUNICATIONS j. RaptorRes. 33(2):160-163 ¸ 1999 The Raptor ResearchFoundation, Inc.

WINTER DtET OF THE B•'4 OWL (Trro AœBA)•'qD LONG-FA_•D OWL (As•o OTUS)IN NORTHEASTERN GREECE: A COMPARISON

HARALAMBOS ALMZATOS 1 Zalihi 4, GR-11524Athens, Greece

VASSILIS GOUTNER Departmentof Zoology,Aristotelian University of Thessaloniki,GR-54006 Thessaloniki, Macedonia, Greece

K•¾ Worn)s: Barn Owl; Tyto alba; Long-earedOwl; Asio species,we calculatedevenness (E)(Ns, • = (N s - 1)/(N• otus; diet;,Greece. - 1), where N• = expH' and N s = 1/52p?)(Alatalo 1981, Marks 1984). In order to compare the dietary overlap There have been severalcomparative studies of the di- between speciesin each wetland, we used Pianka'sIndex (1973), multiplied by 100 to expressit as a percentage. ets of Barn (Tyt0 alba) and Long-eared (Asiootus) Owls (Marti 1974, Amat and Soriguer 1981, Mikkola 1983, De- RESULTS libes et al. 1983, Marks and Marti 1984, Cramp 1985, Capizzi and Luiselli 1996). Dietary information hasbeen The diets of both owls contained small mammals, useful in documentingthe trophic relationshipsin the birds, and insects,in descending order of importance areaswhere the two speciesare sympatric(Herrera and (Table 1). Smallmammals made up 92% of the Barn Owl Htraldo 1976, Marks and Marti 1984). Greece is within diet by number and 85% by biomass.At least 10 mammal the breeding and wintering areasof these species.Infor- specieswere eaten. The most important of them were mation on the diet of Barn Owl in Greece has come Mus spp. (40% by number and 32% by biomass),Microtus mainly from islands and parts of central and western epiroticus(20% and 28%), Apodemusspp. (7% and 10%), Greece(B6hr 1962,Cheylan 1976, Pieper 1977, Nietham- and Crocidurasuaveolens (19% and 8%). Birds of at least ruer 1989, Tsounis and Dimitropoulos 1992). Only a sin- five speciesformed 6% of the diet by number and 15% gle studyhas provided information on the diet of these by biomass.Insects (orthopterans) were a minor diet con- two specieson Euboea Island (Akriotis 1981). This study stituent (2% by number and lessthan 1% by biomass). colnparesthe winter diet of the Barn Owl and the Long- The averageprey weight was 14.7 g (range 0.5-70 g) eared Owl in a Greek wetland area. Prey diversitywas 5.19 and evenness0.67. Mammals made up 89% of the diet by number and STUDY AREA AND METHODS 85% by biomassof Long-eared Owls. We identified at Our studywas conducted in northeastern Greece near least 12 mammalian species in the diet but the main Porto Lagos(40ø99'N, 25ø32'E) in an areawith an exten- mammalian prey were Mus spp. (48% by number and sive coastal wetland complex including lagoons, salt- 35% by biomass),Apodemus spp. (23% and 28%), and M. marshes,mudflats, reedbeds,open cultivatedand uncul- epiroticus(13% and 15%). Birds (at least 16 species) tivated land, small villages, and pinewood plantations. formed 11% of the diet by number and 15% by biomass, Pelletsof Long-earedOwls were collectedat a large com- munal, winter roost in a pinewood and those of Barn while insects(orthopteran, Tettigoniidae) were lessthan Owls were collected in neighboring ruined buildings in 1% by both number and biomass. The average prey February and early March of 1987. Prey were identified weight was16.5 g (range 2-80 g). Prey diversityand even- accordingto Brown et al. (1987), Chaline (1974), and hessvalues were 4.29 and 0.56, respectively,both being MacDonald and Barrett (1993). Mean prey weightswere lower than these of the Barn Owl. taken mainly from Perrins (1987) for birds, MacDonald The proportions of all mammalian prey, in terms of and Barrett (1993) for mammals and fi•om our own data number and biomass,were very similar in both owl spe- for insects. cies. Nevertheless,the proportions of the four most im- We estimated the trophic diversityof birds and mam- portant genera ( Mus, Apodemus,Microtits, and Crocidura) mals in the owl diets at the generic level and that of insectsat a classlevel using the antilog of the Shannon differed significantly(Xs = 208.83, df = 3, P < 0.0001) Index (NB = expH; whereH' -- -•p•lnp, wherep• rep- Crocidura were much more abundant in the Barn Owl's resentsthe proportion of prey items of each genusin the diet while Apodemuswas more common in the Long-eared sample. To standardizediversity for comparisonbetween Owl's diet. Although fewer birds were taken by the Barn

160 JUNE1999 SHORTCOMMUNICATIONS 161

Table 1. Diet of Barn and Long-eared Owls in Porto Lagos.

BARN OWL LONG-EARED OWL

PREY NUMBER % NUMBER % BIOMASS NUMBER % NUMBER % BIOMASS

Insects 7 2.3 0.2 2 0.2 0.1 Tettigoniidae 1 0.3 0.1 2 0.2 0.1 Gryllidae 6 1.9 0.1 ------Birds 18 5.8 14.7 102 10.6 15.5 Alcedo atthis ------I O.1 0.3 Lullula arborea ------2 0.2 0.4 Alauda arvensis ------1 0.1 0.2 Galerida cristata ------9 0.9 1.8 Phylloscopusspp. ------3 0.3 0.2 Erithacus rubecula ------4 0.4 0.5 Turdusspp. ------3 0.3 1.5 Aegithaloscaudatus ------6 0.6 0.3 Parus caeruleus 1 0.3 0.2 2 0.2 0.1 Parusspp. ------4 0.4 0.3 Sturnusvulgaris 3 1.0 4.6 2 0.2 0.9 E,mberizaspp. I 0.3 0.5 2 0.2 0.3 Miliaria calandra 5 1.6 4.4 ------Fringillacoelebs ------11 1.1 1.4 Carduelis chloris ------3 0.3 0.6 Carduelisspp. ------2 0.2 0.2 Serinus serinus ------3 0.3 0.2 Passerspp. 3 1.0 1.6 10 1 1.6 Unident. 5 1.6 3.3 34 3.5 4.3 Mammals 286 92.0 85.1 857 89.2 84.5 Croddura leucodon 6 1.9 1.1 3 0.3 0.2 Crocidura suaveolens 60 19.3 7.9 3 0.3 0.1 Suncus etruscus 2 0.6 O.1 1 O.1 < O.1 Talpaeuropaea ------2 0.2 0.9 Rhinolophusferrumequinum ------I O.1 O.1 Myotissp. ------1 0.1 0.1 Pipistrellussp. 1 0.3 0.1 ------Tadarida teniotis ------1 0.1 0.2 Microtusepiroticus 63 20.3 27.6 121 12.6 15.2 Arvicola terrestris I 0.3 1.3 ------Micromysminutus 2 0.6 0.2 ------Apodemusspp. 23 7.4 10.1 219 22.8 27.6 Rattus rattus 3 1.0 3.9 ------Rattusnorvegicus ------1 0.1 0.4 Rattusspp. ------1 0.1 0.4 Musspp. 125 40.2 31.6 464 48.3 35.1 Unident. Muridae ------33 3.4 3.1 Unident. Rodentia ------6 0.6 1.1 Total 311 100 100 961 100 100

Owl, some larger-sizedspecies (Sturnus, Miliaria) were DISCUSSION proportionallymore common, so bird biomasswas simi- We found small mammals to be the most important lar in the diet of both owls. Average prey weights were prey of both Barn and Long-earedOwls in northeastern similar.Both the total prey overlapand mammalianprey Greece. In other Greek areas, Barn Owls have also been overlapof the two owl specieswere 86%. reported to prey mainly on small mammals (4-15 spe- 162 SHORT COMMUNICATIONS VOL. 33, NO. 2 cles), mice (Mus or Apodemus)being the most important related to this prey's local availability (Bunn et al. 1982, prey by number and usually also by biomass (Akriotis Mikkola 1983). 1981, B6hr 1962, Cheylan 1976, Tsounisand Dimitro- The averageprey weight of the Barn Owl in Porto La- poulos 1992). On some islandssuch as Crete and Corfu, gos was within the limits of the European populations a diverse spectrum of bat specieswas taken but in low (range = 12.8-25 g, Taylor 1994). That of the Long- overall proportions(B6hr 1962, Pieper 1977). In com- eared Owl was much lower than that of the rest of Eu- parison to the Barn Owl's diet in Euboea (Akriotis 1981), rope (37.4 g, Marti 1976), where Microtusspp. (average we found higher biomassproportions of birds (15% vs. weight range = 30-35 g) make up a larger percentageof 3%) and C. suaveolens(8% vs. 1%) but similar propor- the diet (41.5%vs. 12.6%in our study).The lighterprey nons of Apodemus(10% vs. 11%). In contrast,the diet of weight in our studywas primarily due to the preponder- the Long-earedOwls we studied had higher proportions ance of Mus spp. in the diet which weighed only 12 g. of birds (32% vs. 15% by biomass)and Apodemus(34% Average prey weight in the U.S. is even higher than that vs 28%) but those of C. suaveolenswerelow (both <1%). in Europe for both speciesreflecting the availabilityof In Euboea, Long-eared Owls preyed upon somemammal larger-sizedprey species(Taylor 1994). The higher aver- speciesnot found in our study.While owlsprobably differ age prey weight of Barn Owlsin the U.S. may alsosimply in terms of the speciesof mammals they eat in various be due to its larger size than its European relative (Marti habitats (Akriotis 1981, MEHPW 1986), they seemto con- 1974, Marks and Marti 1984, Mikkola 1983). s•stently use mammals as their most common prey Dietary overlap of the two speciesvaried greatly in six source. studiesin the U.S. ranging from 56-90% (Marks and In Europe and the Canary Islands, both owl species Marti 1984). In Spain, overlapwas much higher in winter are alsomainly mammal predators. As in Greece,in some (89%, Delibes et al. 1983) than in summer (69%, Delibes areas the Long-eared Owl's diet can become heavilyre- et al. 1983; 78%, Amat and Soriguer1981). The trophic hant on birds (Mikkola 1983, Amat and Soriguer 1981, diversity(H') of Barn Owlsin our area was0.32 and even- Delgado et al. 1986). Mice and voles, where abundant, ness (E) was 0.29 (calculated according to Herrera, on a are often the main prey of both species,but their relative prey classlevel). Both valueswere much lower than those proportions in diets vary greatly among areas (Cramp reported in Spanishstudies (Herrera 1974) suggesting 1985, Taylor 1994). In the U.S., both owl speciesare pri- that Barn Owl in northeastern Greece have a more sten- marily mammalian predators but the Long-eared Owl ophagic diet and that, unlike the Mediterranean region, tends to prey on Microtusspp. in lower proportionsthan prey in Greece,especially some small mammals, are prob- the Barn Owl, taking fewer birds than in Europe (2% vs. ably not in short supplyfor owls.The high dietary over- 14% by biomass)(Marti 1976, Marks and Marti 1984). lap we found between the two owl species,coupled with Bunn et al. (1982) have described the Barn Owl as an the similarity in averageprey weights,suggested that the unspecializedpredator of small mammals while Taylor two speciesare grouped along their food dimension and (1994) suggestedthat it showsa definite preference for belong to the sametrophic guild of owlswintering in this Microtusbecause they are of small size and easyto cap- area. ture. Long-earedOwls seem to concentrateon relatively Also in other areas, where the Barn and Long-eared few mammal speciesregardless of habitat type or location Owl are syntopic,Barn Owls have been shown to have a they are found (Marti 1974). There is controversywheth- broader diet (Marti 1976, Amat and Soriguer 1981, Veiga er Microtusare selectedor simplytaken accordingto their 1981, Capizzi and Luiselli 1996). This probably results availability (Mikkola 1983, Cramp 1985). As far as the from the high dietary overlap betweenthem and it may availabilityof small mammals in our area is concerned, facilitatetheir coexistencein areasof syntopy(Marks and among 93 individuals snap-trapped at Porto Lagos area Marti 1984). The noticeable difference in the bird spe- betweenJune 1984-October 1986, 48% were Mus spp. cies composition in the diets of the two owl speciesin (41% M. abbotti),38% Crocidurasuaveolens, 11% Apodemus our area may simplyhave been related to differencesin sylvaticus,and 3% Microtusepiroticus (Vohralik and Sofian- their hunting habits.Although both forage in the open, idou 1992). Trapping resultsmay not reflect the true pro- Long-eared Owls also hunt under tree canopy (Cramp portions of small mammals in their habitats (Yom-Tov 1985) (which may alsoaccount for the higher proportion 1991, Blem et al. 1993), but we felt they were a good of Apod•nustaken) and they alsoraid bird roostsin bush- indicator of the relative abundance of small mammals in es and trees to a much greater extent than Barn Owls. our studyarea. They indicated that mice Muswere mostly taken by both owlsprobably because they were plentiful. RESUMEN.--EnPorto Lagos (noreste de Grecia), las die- M. epiroticuswas somewhatpreferred by both and Croci- tas de invierno de Tytoalba y Asio otusconsistieron b•tsi- dura suaveolenswas generally avoided, especiallyby the camente de pequefiosroedores (en ambos 85% de la Long-eared Owl that seemed to prefer Apodemus.Al- biomasa). Ratones (Mus y Apodemus)y ratas (Microas epz- though shrewsare in general distastefulto many preda- roticus)fueron las presasmas importantes para ambosbu- tors, including the Long-earedOwl, Barn Owlshave been hos. Las musarafias(Cr0cidura) fueron importantes sola- found to take them in large numbers,a fact frequently mente para Tyro alba (8% de la biomasa). Las JUNE1999 SHORTCOMMUNICATIONS 163

proporcionesde las presasde los cuatro mamlferosmas (Athene noctua) en una misma localidad de Castilla la abundantes rueton significativamentediferentes entre Vieja. Ardeola30:57-63. los buhos. Mas especiesde aves rueton capturadaspot HERRERA,C.M. 1974. Trophic diversityof the Barn Owl Asiootus (16 vs. 5) pero la contribuci6n a la biomasarue Tyto alba in continental western Europe. Ornis Scand similarpara los dos (15%). E1promedio del pesode las 5:181-191. presasrue similar (Tyroalba: 14.7 g; Asiootus: 16.5 g), la -- ANDF. HIRALDO.1976. Food-nicheand trophic re- diversidad de presas rue mayor en Tyroalba (5.19 vs. lationshipsamong European owls. OrnisScand. 7.29- 41. 4.29). Las dietas coincidieron en un 86%. MACDONALD, D. AND P. BARRETT. 1993. Mammals of Brit- [Traducci6n de Casar Mgrquez] ain and Europe. Harper Collins, London, U.K. LITERATURE CITED MARTI, C.D. 1974. Feeding ecology of four sympatnc owls. Condor 76:45-61. AKRIOTIS,T. 1981. Food ecologyof five sympatricowls. 1976. A review of prey selection by the Long- First Degree dissertation,Wolfson College, Oxford eared Owl. Condor 78:331-336. Univ., Oxford, U.K. MARKS,J.S. 1984. Feeding ecology of breeding Long- AM^T,J.A. ANDR.C. SOPaOUER.1981. Analyseconparative eared Owls in southern Idaho. Can.J. Zool.62:1528- des ragimes alimentairesde l'Effraie Tyroalba et du 1533. Moyen-Duc Asio otus dm•s L'Ouest de L'Espagne. --AND C.D. MARTI. 1984. Feeding ecology of sym- Alauda 49:112-120. patric Barn Owls and Long-earedOwls in Idaho. Ornzs ALATALO, R.V. 1981. Problems in the measurements of Scand. 15:135-143. evennessin ecology.Oikos 37:199-204. MINISTRY OF ENVIRONMENT, HOUSING AND PUBLIC WORKS BLEM,C.R., LB. BLEM,J.H. FELIXAND D.W. HOLT. 1993. (MEHPW). 1986. Project for delineation of Ramsar Convention wetlands. Wetland: Lake Vistonis-Porto Estimation of body massof volesfrom crania in Short- Lagos. MEHPW, Athens, Greece (in Greek). eared Owl pellets. Am. Midl. Nat. 129:281-286. MIKKOLA,H. 1983. Owls of Europe. T. & A.D. Poyser, BOHR,H.-J. 1962. Zur kenntnis der Vogelweltvon Korfu. Carlton, U.K. Bonn. Zool. Beitr. 13:50-114. NIETHAMMER,J. 1989. Gew61inhalte der Schleiereule BROWN,R.,J. FF•RGUSON,M. LAWPENCE ^ND D. LEES.1987. (Tyto alba) von Kos und aus Sfidwestanatolien.Bonn Tracks and signs of the birds of Britain and Europe. Zool. Beitr. 40:1-9. Helm, London, U.K. PERPaNS,C.M. 1987. Collins new generation guide to the BUNN, D.S., A.B. WARBURTON^ND R.D.S. WILSON. 1982. birds of Britain and Europe. Collins, London, U.K. The Barn Owl. T. & A.D. Poyser,Carlton, U.K. PIANKA,E.R. 1973. The structure of lizard communities. CAPIZZI,D. AND L. LUISELLI.1996. Feeding relationships Annu. Rev.Ecol. Syst. 4:53-74. and competitiveinteractions between phylogenetical- PIEPER,H. 197W'Flederm/iuse aus Schleiereulen-Gew61- ly unrelated predators (owls and snakes).Acta Oecol. len von der Insel Kreta. Z. SSugetierkd.42:7-12. 17:265-284. TAYLOR,I. 1994. Barn Owls: predator-preyrelationships CHALINE,J. 1974. Les proies des rapaces.DOIN Editeurs, and conservation.University Press, Cambridge, U.K. Paris, France. TSOUNIS, g. AND A. DIMITROPOULOS.1992. Seasonal vari- CHEYLAN,G. 1976. Le regime alimentaire de la chouette ation of the feeding of Barn Owl, Tyto alba (Scopoh effraie Tyto alba en Europe Mediterraneenne. Rev. 1769) in mount Hymettus,Attica, Greece. Biol. Gallo- Ecol. (TerreVie) 4:565-579. hell. 19:29-36. CRAMP,S., [Ed.]. 1985. The birds of the western Palearc- VEICA,J.P. 1981. Variacion anual de regimen alimenticio tic. Vol. 4. Oxford Univ. Press, Oxford, U.K. y densidadde poblacionde dos estrigiformes:sus cau- sas. Do,iana Acta Vert. 8:159-175. DELGADO,G., V. QUILLS,A. MARTINAND K. EMMERSON. VOHRALIK, V. AND W.S. SOFIANIDOU. 1992. Small mammals 1986. Alimentacion del Buho Chico (Asio otus) en la (Insectivora, Rodentia) of Thrace, Greece. Acta Unzv isla de Tenerife y analisiscomparativo con la dieta de Carol. 36:341-369. Tytoalba. Do,iana, Acta Vert. 143:87-93. YOM-TOV,Y. 1991. Character displacementin the psam- DELIBES,M., P. BRUNET-LACOMPTEAND M. M•EZ. 1983. mophileGerbillidae of Israel. Oikos60:173-179. Datos sobre la alimentacion de la lechuza comun (Tyto alba), el buho chico (Asio otus)y el mochuelo Received 15 April 1998; accepted6 February 1999