Acrocephalus 2.J (128-129): 59-63, 2006 Birds in the Diet of Barn Owl Tyto alba in SE Bulgaria Ptice v prehrani pegaste sove Tyto alba v JV Bolgariji Boyan Milchev1, Zlatozar Boev2 & Valeri Georgiev3 1 University of Forestry, Wildlife Management Department, 10 Kl. Ochridski Blvd., BG-1756 Sofia, Bulgaria, e-mail: boyan.m@ltu.bg 2 National Museum of Natural History, Tzar Osvoboditel 1, BG-1000 Sofia, Bulgaria, e-mail: boev@nmnh.bas.bg 3 Ministry of Environment and Water, Maria Luisa 22, BG-1000 Sofia, Bulgaria, e-mail: nnpsf@moew.government.bg Forty avian species of 4 orders have been detected in the diet of Barn Owl Tyto alba at 28 breeding localities in SE Bulgaria, with 24 species recorded as prey for the first time in the country. Passeriformes represent 99% by number and 96% by biomass of birds. House Sparrow Passer domesticus is the dominant species, representing 34% of prey individuals and 30% of the prey biomass from birds. The mean body weight of the individual avian prey is 31.5 g. The presence of birds in the diet of Barn Owl has decreased five- to tenfold during the last three to four decades. The number of the synanthropic bird species has significantly declined, while the share of the openland, scrubland and woodland species has significantly increased. Key words: birds, Barn Owl, Tyto alba, diet Klju~ne besede: ptice, pegasta sova, Tyto alba, prehrana 1. Introduction 2. Material and methods Barn Owl Tyto alba preys mainly on small mammals, which constitute up to 90% of its diet. Birds comprise a much smaller share (Mikkola 1983, Cramp 1985, Glutz von Blotzheim & Bauer 1991, Taylor 1994, Roulin 2004). Specialized predation on birds is an exception for this species (Görner 1978, Glutz von Blotzheim & Bauer 1991). Usually, House Sparrow Passer domesticus is the most common avian prey species. Research in Bulgaria in the 1960s and 1970s showed that birds represented between 7.5 and 18.2% by number of prey individuals, where House Sparrow accounted for 72.8 to 82.3% of the avian prey individuals (Simeonov 1978, Simeonov et al. 1981). Pellets from 32 Barn Owl breeding sites in SE Bulgaria showed that birds are only 1.5% of the number of prey individuals, and that the House Sparrow represents up to 33.5% of the avian prey (Miltschev et al. 2004). This paper examines bird species composition and distribution in the diet of Barn Owl in SE Bulgaria. The characteristics of the study area and the methods for collecting and identifying material have been described by Miltschev et al. (2002) and Miltschev et al. (2004). The avian component in the diet of Barn Owl were examined at 28 breeding sites (UTM coordinates of a 10-km grid: MG05, MG37, MG39, MG45, MG47, MG48, MG59, MG64, MG66, MG68, MG76, MG89, MG99, MH10, MH20, MH60, MH80, MH90, NG09, NG18, NG24, NG38, NG39, NG49, NG67, NH00, NH01, NH30). Sites without avian prey species are not part of the study. The birds have been identified by their bone remains, using the comparative osteological collection of “Fossil and Recent Birds Department” of the National Museum of Natural History, BAS. The feathers have been determined by J. Menzel. The body mass of the prey species is given according to Glutz von Blotzheim & Bauer (1991). Incompletely identifiedpasserines(Oscines)andspecimensidentified 59 B. Milchev et al.: Birds in the Diet of Barn Owl Tyto alba in SE Bulgaria to a genus that includes species with different habitat preferences were excluded in the distribution of prey according to their main habitats. Statistical differences in frequencies of the ecological groups were calculated by a chi-square test, with ? < 0.05 for significance. 3. Results Table 1 gives the composition of birds in the diet of Barn Owl. The prey species come from four orders of birds, where the passerines (Passeriformes) were present at all sites and represent 98.65% by number and 95.63% by biomass of all birds. Sparrows (Passeridae) and Swallows (Hirundinidae) as the commonest prey - 36% and 10% by number (Figure 1). Both families are mainly synanthropic. The House Sparrow is the dominant species and only two other species, Barn Swallow Hirundo rustica and Starling Sturnus vulgaris, have over 5% by number. They comprise 47% by number of all birds as prey. Three species surpass 5% by Table 1: Birds in the diet of the Barn Owl Tyto alba in SE Bulgaria Tabela 1: Ptice v prehrani pegaste sove Tyto alba v JV Bolgariji Bird taxa / Takson ptic Frequency on locations/ N Frekvenca po lokacijah (%) Coturnix coturnģx 1 3.57 Porzana parva 1 3.57 Porzana pusilla 1 3.57 Athene noctua (juv.) 2 7.14 Dendrocopos minor 1 3.57 Calandrella sp. 2 7.14 Alauda arvensis 18 39.29 Galerida 1 Mehinocorhypha 4 10.71 Hirundo rustica 23 25.00 Delichon urbica 13 3.57 Motacilla alba 2 3.57 Motacilla flava 8 17.86 Anthus sp. 2 7.14 Troglodytes troglodytes 2 7.14 Prunella modularis 1 3.57 Turdinae 1 3.57 Phoenicurus phoenicurus 1 3.57 Phoenicurus sp. 1 3.57 Saxicola torquata 2 3.57 Turdus philomelos 1 3.57 Turdus merula 2 7.14 Sylvidae 2 7.14 Sylvia sp. 2 7.14 Acrocephalus scirpaceus 1 3.57 Acrocephalus sp. 2 3.57 Locustella luscinoides 3 10.71 Hippolais pallida 1 3.57 Phylloscopus collybita 1 3.57 Proportion by number/ Proportion by biomass/ Dele` po {tevilu (%) Dele` po biomasi (%) 0.27 0.86 0.27 0.47 0.27 0.38 0.54 2.66 0.27 0.21 0.54 0.51 4.86 5.56 1.08 1.37 6.22 4.15 3.51 2.12 0.54 0.36 2.16 1.24 0.54 0.34 0.54 0.15 0.27 0.15 0.27 0.56 0.27 0.12 0.27 0.13 0.54 0.21 0.27 0.57 0.54 1.49 0.54 0.21 0.54 0.25 0.27 0.09 0.54 0.19 0.81 0.37 0.27 0.08 0.27 0.06 6c ACROCEPHALUS 2.J (128-I29): $9-63, 200C continuation of Table 1 / nadaljevanje tabele 1 Bird taxa / Takson ptic Frequency on locations (%)/ N Frekvenca po lokacijah (%) Proportion by number (%)/ Dele` po {tevilu (%) Proportion by biomass (%)/ Dele` po biomasi (%) Phylloscopus trochilus 1 3.57 0.27 0.07 Phylloscopus sp. 2 7.14 0.54 0.14 Parus lugubris 2 7.14 0.54 0.33 Parus major 2 7.14 0.54 0.33 Aegithalos caudatus 1 3.57 0.27 0.07 Remiz pendulinus 1 3.57 0.27 0.08 Lantus collurio 1 3.57 0.27 0.25 Lanius senator 1 3.57 0.27 0.26 Sturnus vulgaris 25 25.00 6.76 16.09 Passer domesticus 124 67.86 33.51 30.33 Passer montanus 10 21.43 2.7 1.97 Fringilla coelebs 3 10.71 0.81 0.57 Carduelis carduelis 4 10.71 1.08 0.55 Carduelis chloris 4 14.29 1.08 0.96 Carduelis cannabina 6 14.29 1.62 0.93 Carduelis sp. 1 3.57 0.27 0.15 Coccothraustes coccothraustes 7 21.43 1.89 3.30 Emberiza cia 1 3.57 0.27 0.21 Emberiza cirlus 1 3.57 0.27 0.21 Emberiza citrinella 4 10.71 1.08 1.00 Emberiza schoeniclus 1 3.57 0.27 0.15 Miliaria calandra 9 28.57 2.43 3.75 Emberiza sp. 5 14.29 1.35 1.12 Oscines 53 42.86 14.32 12.31 Total 370 28 locations 100 11.651 g biomass: House Sparrow, Starling, and Skylark Alauda arvensis. They total 52% by biomass. Only these four species and the Corn Bunting Miliaria calandra were captured in more than 25% of the study sites. The average body weight of the captured birds is 31.5 g. Young Little Owl (Athene noctua – 155 g) and Quail (Coturnix coturnix – 100 g) are the heaviest prey, while Chiffchaff Phylloscopus collybita – 7.5 g) is the lightest prey of Barn Owls. Synanthropic birds (65% by number) (Table 2), followed by the open-area birds (16%) and the woodland and shrubland birds (16%), are the most common prey. Thus, settled areas, open areas, wood and shrub habitats comprise the main hunting grounds for birds by Barn Owls in SE Bulgaria. 4. Discussion The Barn Owl hunts mostly small, communally roosting birds as sparrows, swallows, starlings, finches (Fringillidae) and thrushes Turdus spp. (Cramp 1985, Glutz von Blotzheim & Bauer 1991, Mebs & Scherzinger 2000). The first four groups are the most common prey species in SE Bulgaria. Turdids are an exception, representing barely 2% by number, in view of the wide distribution of Turdus species in the hunting territories of the Barn Owl. Species of two other families, Alaudidae and Emberizidae, occur more often in the diet: Skylark and Corn Bunting were the most frequent prey. They are common breeding birds in the region and also occur in flocks during the non-breeding period, therefore fitting the description of the commonest bird prey species. 61 [OO B. Milchev et al.: Birds in the Diet of Barn Owl Tyto alba in SE Bulgaria Figure 1: Bird families representation in the diet of the Barn Owl Tyto alba in SE Bulgaria by percent of number of species Slika 1: Pti~je dru`ine v prehrani pegaste sove Tyto alba v JV Bolgariji po procentu {tevila vrst The variety of bird species preyed upon is much wider than previously known for Bulgaria (Simeonov 1978, Simeonov et al. 1981). This study establishes 24 avian species for the first time in Bulgaria as Barn Owl prey. These results likely stem from the much larger sample, as analyzed by Miltschev et al. (2004). The Barn Owl is not a strictly specialized predator on a small number of bird species. The number of the bird species recorded increases with the increasing number of the sites examined and the variety of habitats of the hunting grounds. In contrast to the previous research in Bulgaria (Simeonov 1978, Simeonov et al. 1981), the Barn Owl has a reduced relative share of birds in its diet by five- to ten-fold. Now they represent 1.5% by number of prey in SE Bulgaria (Miltschev et al. 2004), and 2.3% in the NW part of Upper Thracian Plane (Miltschev et al. 2006). Statistically very significant differences exist in the distribution of birds by habitats (?2 = 53.63, p < 0.001) (Table 2). The synanthropic birds constitute over 90% by number in the previous studies, where the House Sparrow exceeded 70% of all bird prey species (Simeonov 1978, Simeonov et al. 1981). Data for the last five years show a significant decrease in the share of synanthropic birds and significant increase in birds of non-settled areas, fallow land, woodland and shrubland habitats. The decrease in synanthropic birds is due to the 50% decline of House Sparrow in the Barn Owl diet. Until now, the larger share of the House Sparrow and some other commensal species in the Barn Owl diet in Eastern Europe has been explained by intact traditional methods of agriculture and the traditionally developed practices of harvesting and food storage (Taylor 1994, Schmidt 1973). We could only speculate that the House Sparrow has become less profitable prey for Barn Owl after 1991, when private land-ownership and farms, more careful harvesting and storage of harvests, replaced the former mode of agriculture and stock-breeding typical of the socialist cooperative farms (own data). That transformation could explain why the House Sparrow population decreased and the species became more difficult prey. Nevertheless, the increased share of the openland, woodland and shrubland species, chiefly of larks, finches and buntings taken together, do not compensate for the drastic decline of House Sparrows. More likely, in the absence of another small common bird species as alternative prey to replace the House Sparrow, Barn Owl hunting of birds has decreased. Acknowledgments: We thank Mr J. Menzel for the identification of the feathers. We express our deep gratitude to Dr J. Weigand for improving the English. Table 2: Distribution of birds in the diet of the Barn Owl Tyto alba in Bulgaria according to preferred nesting habitats (% by number). Tabela 2: Razporeditev ptic v prehrani pegaste sove Tyto alba v Bolgariji glede na izbrani gnezditveni habitat (% po {tevilu). Habitats / Habitati open areas / odprte povr{ine wetlands / mo~virja urban areas / urbana obmo~ja woodland and shrubland / gozdovi in grmi{~a Simeonov (1978) Simeonov et (1981) al. Miltschev et (2006) al. Present study/ ta {tudija 0.5 3.1 10.1 15.7 0 3.4 3.0 3.3 994 90.1 72.7 65.0 0.1 3.4 14.1 16.0 62 Acrocephalus 2.J (128-129): 59-63, 2006 5. Povzetek V prehrani pegaste sove Tyto alba na 28 gnezdi{~ih v jugovzhodni Bolgariji so bili odkriti 4 redovi ptic, med katerimi je bilo 24 vrst ptic, kot sovji plen zabele`enih prvi~ v tej dr`avi. Pevke so bile zastopane z 99% po {tevilu in 96% po biomasi ptic. Prevladujo~i plen je bil doma~i vrabec Passer domesticus, in sicer s 34% uplenjenih osebkov in 30% biomase pti~jega plena. Povpre~na telesna te`a plena je zna{ala 31,5 g. Dele˛ ptic v prehrani pegaste sove se je v zadnjih treh do {tirih desetletjih zmanj{al za pet- do desetkrat. [tevilo sinantropnih vrst se je ob~utno zmanj{alo, medtem ko se je dele` ptic odprte pokrajine, grmi{~ in gozdov v precej{nji meri pove~al. 6. References Cramp, S. (ed.) (1985): The birds of the western Palearctic, Vol. 4. - Oxford Univ. Press, Oxford. Glutz von Blotzheim, U. & Bauer, K. (1991): Handbuch der Vögel Mitteleuropas, Bd. 9. - Aula, Wiesbaden. Görner, M. (1978): Schleiereule, Tyto alba, als Vogeljäger. - Beitr. Vogelkd. 24 (5): 273-275. Mebs, T. & Scherzinger, W. (2000): Die Eulen Europas. Biologie, Kennzeichen, Bestand. - Franckh-Kosmos Verl.-GmbH & Co., Stuttgart. Mikkola, R. 1983: Owls of Europe. - T. & A.D.Poyser. Calton. Miltschev, B., Georgiev, V. & Kovatschev, A. (2002): Brutbestand und Brutplatzwahl der Scleiereule (Tyto alba) in Südost-Bulgarien. - Egretta 45: 114-120. Miltschev, B., Boev, Z. & Georgiev, V. (2004): Die Nahrung der Schleiereule (Tyto alba) in Südost-Bulgarien. - Egretta 47: 66-77. Milchev, B., Boev, Z. & Kodjabashev, N. (2006): Breeding distribution and diet composition of the Barn Owl (Tyto alba (Scopoli, 1769)) (Aves: Strigiformes) in the North-Western Upper Thracian Plane (Bulgaria). -Acta zool. bulg. 58 (1): 83-92. Roulin, A. (2004): Covariation between plumage colour polymorphism and diet in the Barn Owl Tyto alba. - Ibis 146: 509–517. Schmidt, E. (1973): Über die Vogelnahrung der Schleiereule Tyto alba und der Waldohreule Asio otus in Ungarn. -Ornis Fennica 49 (3-4): 98-102. Simeonov, S. (1978): Über die Nahrung der Schleiereule (Tyto alba Scopoli) in einigen Gegenden Bulgariens. - Ecology, Sofia 4: 65-71. (In Bulgarian with English summary). Simeonov, S., Michev, T. & Simeonov, P. (1981): Materialien zur Brutverbreitung und zum Nahrungsspektrum der Schleiereule (Tyto alba (Scopoli)) in Bulgarien. - Ecology, Sofia 8: 49-54. (In Bulgarian with English summary). Taylor, I. (1994): Barn Owls: predator-prey relationships and conservation. - Cambridge Univ. Press., Cambridge. Arrived / Prispelo: 29.11.2005 Accepted / Sprejeto: 5.10.2006 63