Materials and methods Data collectionThe Kazanlak Valley covers around 800 km2 in the moderate continental climate zone between the Stara Planina Mountains to the north and the Sredna Gora Mountains to the south. Open areas with farmland, extensive pastures, and meadows dominate the landscape around villages in the valley (see also Milchev, 2012;Milchev and Gruychev, 2014). Food remains from both intact and disintegrated pellets were collected from around nests and roosting sites in 28 breeding localities in mid-June and early September 2012 and for 2 nests additionally in mid-July 2013, a total of 30 localities. Pellets were possibly deposited over several breeding seasons, but most of them came from 2012 deposits.Prey mammals were identified according to Popov and Sedefchev (2003) and the author's own comparative

Coexistence of predator species often depends on behaviours or preferences that result in spatio-temporal reduction of competition. In this study, the diets of coexisting barn owls (Tyto alba) and eagle owls (Bubo bubo) in an agricultural landscape of SE Bulgaria were compared. White-toothed shrews (Crocidura spp.), voles (Microtus spp.) and mice (Mus spp.) were the main prey of barn owl (86.3% by number, 81.2% by biomass) with significantly different frequencies in annual diets. The principle biomass (64.8 ± 6.2%) of the significantly different eagle owl annual diets comprised much heavier prey such as white-breasted hedgehog (Erinaceus roumanicus), European hare (Lepus europaeus) and non-passerine birds of wetlands and open habitats. The two owl species preferred and hunted on different prey size groups in the same territory, and this difference explained the low level of food competition (6.0 ± 3.6% diet overlap according to prey biomass). Voles were the only prey of the two owls with significantly different frequencies for the annual diets in intraspecies comparisons. The proportions of voles in both diets showed similar trends during the study. Eagle owl predation on barn owls was slightly affected by their coexisting breeding despite the high levels of food stress of eagle owl. These findings provide insight into how preying habits can predict successful coexistence of potentially competing predator species.

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Three cases of carrion-feeding with remains of artiodactyls (0.3%, n=1104 samples with food remains) have been documented in a long term diet study of Eurasian Eagle-owls (Bubo bubo) in 53 localities at Southeastern Bulgaria. Bone pieces of a sheep/goat (Ovis aries/Carpa hircus), a Fallow Deer (Dama dama) and a Domestic Pig (Sus scrofa dom.) in three Eurasian Eagle-owl breeding localities (5.7%) prove extremely rare feeding on carrion. Northern White-breasted Hedgehog (Erinaceus roumanicus), rats (Rattus sp.), waterbirds and gallinaceous birds (total 59.5-72.6% by biomass) constituted the main portion of the diets with carrion remains. The comparisons between food niche breadths, diet composition, average prey biomass and values of superpredation of the annual diets in the three localities have not supported the carrion-feeding of the Eurasian Eagle-owl as a result of food shortages. Keywords: feeding ecology, pellet analysis, dietary breadth, owl dietÖsszefoglalás Az uhu (Bubo bubo) hosszútávú, 53 délkelet-bulgáriai költőhelyen végzett táplálkozásbiológi-ai vizsgálata során eddig csak három esetben találtak párosujjú patás maradványokat (1104 maradvány minta 0,3%-a). Többségében birka/kecske (Ovis aries/Carpa hircus), egy európai dámvad (Dama dama) és egy házi sertés (Sus scofa dom.) csontmaradványai, három uhu költőhelyen (5,7%), bizonyítják, hogy mennyire ritkán táp-lálkozik ez a faj döggel. Az uhu fő táplálékforrását (59,5-72,6%) keleti sün (Erinaceus roumanicus), patkányfa-jok (Rattus sp.), vízimadarak és tyúkalakúak adják. A táplálkozási niche-szélesség, a fő prédaállat gyakorisága, az átlagos préda biomassza és az éves szuperpredáció értékeinek összehasonlítása alapján egyik területen sem a táp-lálékhiány okozza az uhu dögevését.

The diet of non-breeding White Storks was studied by pellet analysis and included mainly insects (99.9%, n=28947) with a predominance of grasshoppers (Orthoptera, 76.1%), and beetles (Coleoptera, 26.1%). The bush crickets Decticus albifrons/verrucivorus were the most numerous prey (29.9% by items), occurring in almost all pellets (98% occurrence in pellets, n=147) and predominating in half of them (49.7%). The grasshopper associations in the pellets specify foraging mainly in mesophytic grasslands that usually replace abandoned fields and overgrown pastures with a low level of grazing. The xerophytic grass-shrubby habitats, not rare on stony terrains, were of less importance, providing around 20% by prey. The typical aquatic inhabitants and the use of carrion around villages were exceptions in the study diet. The number of innutritious materials in the pellets rose when the White Storks hunted on nippy and agile grasshoppers and decreased when the main pray was slower beetles taken from the ground. The roosting of non-breeding White Storks disappeared when their preferred feeding habitats were ploughed up in the following years