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.