Belg. J. Zool., 135 (2) : 109-118 July 2005 Contribution to the study of the diet of four owl species (Aves, Strigiformes) from mainland and island areas of Greece Haralambos Alivizatos1, Vassilis Goutner2 and Stamatis Zogaris3 1 4 Zaliki Street, GR-11524 Athens, Greece 2 Department of Zoology, School of Biology, Aristotelian University of Thessaloniki, GR-54124, Thessaloniki, Greece 3 40 Perrikou Street, GR-11524 Athens, Greece Corresponding author : Vassilis Goutner, e-mail : [email protected] ABSTRACT. The diets of the Barn Owl (Tyto alba), Little Owl (Athene noctua), Long-eared Owl (Asio otus) and Eagle Owl (Bubo bubo) were studied through analysis of pellets collected at 13 different continental areas and islands of Greece. The most important prey of the Barn Owl was mammals (mainly Microtus, Mus, Apodemus, Rat- tus and Crocidura), although birds and amphibians were of some importance on Antikythera island and Potidea (Central Macedonia), respectively. Average prey biomass ranged from 12.5 g to 42.8 g. The median prey biomass differed significantly between areas (p<0.001). The diet of the Little Owl was more diverse, consisting mainly of mammals (mostly Microtus, Mus, Apodemus, Micromys and Crocidura) in the Evros and Axios Deltas, mainly of insects (mostly Orthoptera and Coleoptera) in the Kitros Lagoon, Psara and Tilos islands, while birds and reptiles were common supplementary prey. Average prey biomass ranged from 0.7 g to 11.9 g. The median prey biomass differed significantly between the areas studied (p<0.001). The diet of the Long-eared Owl in both Nestos Delta and Porto Lagos consisted mainly of mammals (mostly Microtus, Mus and Apodemus), with some reptiles in the former area and birds in the latter. Average prey biomass was 18.5 g and 19.5 g respectively. The median prey bio- mass did not differ significantly between the two areas. The diet of the Eagle Owl in the Amvrakikos wetland con- sisted mostly of birds (62 % by biomass) and mammals (36 %, mainly Rattus norvegicus). Insects were the most important prey by numbers - 47 % (1% by biomass). The prey diversity of the Eagle Owl was the highest while that of the Barn Owl was the lowest. Prey use by owls tended to clump by geographic area. We conclude that the owl species studied make use of prey according to the local availability and in accordance to the hunting abilities of each species. KEY WORDS : Barn Owl Tyto alba, Little Owl Athene noctua, Long-eared Owl Asio otus, Eagle Owl Bubo bubo, diet, feeding ecology, Greece. INTRODUCTION MATERIAL AND METHODS The study areas (Fig. 1) encompass different habitats. Studies carried out on the diet of owls (Strigiformes) in The Evros, Nestos and Axios Deltas, as well as Porto Europe have revealed considerable geographical variation Lagos, Kitros Lagoon and Amvrakikos area are major in the diet of each species (BUNN et al., 1982; MIKKOLA, wetlands, with a high diversity of habitats, such as salt- 1983; CRAMP, 1985; TAYLOR, 1994). Generally, prey marshes, lagoons, reedbeds, tamarisk and riparian forest, composition and diversity in the Mediterranean area are marshes and cultivations (MEHPW, 1985; 1986a; different to those in central and northern Europe (HER- 1986b). Potidea and Parthenio areas, both in central Mac- RERA & HIRALDO, 1976). edonia, include mainly agricultural land. The study sites in Mt. Hymettus and Avlona (both near Athens) include In Greece, nine owl species are known to occur and open scrublands (phrygana) habitat and farmland. The islands of Psara (NE Aegean), Tilos (SE Aegean) and some of them are common in both continent and island Antikythera (between Peloponese and Crete) include habitats (HANDRINOS & AKRIOTIS, 1997) but dietary stud- mainly phrygana and (to a lesser extent) farmland. ies are scarce. The aims of this study were : a) to describe Pellets were collected opportunistically from roosts and compare the diet and feeding ecology of the Barn between December 1997 and August 2001 (Table 1). The Owl (Tyto alba (Scopoli, 1769)), Little Owl (Athene noc- material was collected out of the breeding season, mostly tua (Scopoli, 1769)), Long-eared Owl (Asio otus (Lin- in winter, excepting that of the Eagle Owl collected at naeus, 1758)) and Eagle Owl (Bubo bubo (Linnaeus, nests. Pellets were analyzed using reference books 1758)) studied in various parts of Greece and, b) to com- (Mammals : LAWRENCE & BROWN, 1973; CHALINE, 1974. pare our results with those of studies carried out in Greece Birds : BROWN et al. (1987). Reptiles : ARNOLD & BUR- and other European countries. TON (1980). Insects : CHINERY (1981)). The average 110 Haralambos Alivizatos, Vassilis Goutner and Stamatis Zagoris weight of each prey taxon was taken from the literature M. rossiaemeridionalis was by far the most important (Mammals : MACDONALD & BARRET (1993). Birds : PER- prey species (84%). The relative contributions of other RINS (1987). Reptiles : HELMER & SCHOLTE (1985). mammal species were below 5%. Birds formed only a Insects : ZERUNIAN et al. (1982)). Because of the diffi- minor part of the diet in this area (2%). culty of distinguishing mice Mus spp. and Apodemus spp. from skulls (VOHRALIK & SOFIANIDOU, 1992), these were TABLE 1 often not separated by species. Average prey weight for Number of samples collected in each study area each sample was estimated by multiplying the numbers of each prey by its average weight, adding the weights pro- Athene Asio Bubo Area Tyto alba duced and dividing the sum by the total numbers of prey noctua otus bubo in each sample. The trophic diversity (NB) was estimated by using the antilog of the Shannon-Weiner index, while Evros Delta 4 6 - - Porto Lagos 1 - 1 - in order to standardize the trophic diversity for compari- Potidea 1 - - - son within and between the areas we calculated evenness Parthenio 1 - - - index. Both were calculated on a class prey level. The Hymettus 2 - - - Mann-Whitney U-test or Kruskall-Wallis test (where Avlona 1 - - - appropriate) compared the median prey weights of the Antikythera 1 - - - same species. Cluster analysis was also performed (using Axios Delta - 3 - - Euclidean distances as distance measure and single link- Kitros Lagoon - 1 - - age as a linkage rule) on biomass proportions of prey in Tilos - 1 - - order to determine geographical relationships in the owls’ Psara - 1 - - diet. The author names of prey identified in pellets of the Nestos Delta - - 1 - owls studied are indicated in Appendix 5. Amvrakikos - - - 2 In Potidea, mammalian prey dominated (at least seven species, 92% by biomass). The main prey species was M. macedonicus (74 %). Of moderate importance were Apodemus spp. (7%), C. suaveolens (6%), birds (7%) and frogs (Rana spp.) (6%). In Parthenio, various species of mammals composed the greater part of the diet, although birds, amphibians and insects were also present. The most important species by biomass were M. rossiaemeridionalis (35%), M. mac- edonicus (21%), Rattus spp. (15%), and Apodemus syl- vaticus (12%), while birds formed 7% of the diet. Inver- tebrates were unimportant in the diet. In Mt. Hymettus, at least eight mammalian species made up 92% of the diet by biomass. The most important prey species by biomass were A. sylvaticus (35%), A. mystacinus (33%) and Microtus thomasi (8%). Other species’ participation did not exceed 5%. Birds formed 8% of the diet. In Avlona, mammals again were the most important Fig. 1. – Map showing the areas where pellets of owls were col- prey of the Barn Owl (eight species, 96% by biomass) lected for this study. and birds were also represented (4%). The most impor- tant species by biomass was M. thomasi (49%), followed by Mus domesticus (25%), M. macedonicus (8%) and RESULTS A. sylvaticus (6%). In Antikythera Island, the main prey consisted of three Barn Owl species of mammals (83% by biomass). By far the most important prey was Rattus rattus (73%) followed by birds In the Evros Delta, small mammals (including at least (16%) and M. domesticus (6%). Reptiles were repre- 10 species) composed 90% of the Diet of the Barn Owl sented by geckoes (Gekkonidae) and formed 10% of the (Appendix 1). The most important prey species by bio- diet by number but only 1% by biomass. mass was Microtus rossiaemeridionalis (37%) followed The median prey biomass was significantly different by Mus spp. (20%), Crocidura suaveolens (12%) and between the seven areas (Kruskall-Wallis test, 2 = Arvicola terrestris (7%). Birds were moderately impor- x 304.04, df = 6, p<0.001). Average prey biomass ranged tant by biomass (9%). Amphibians and arthropods from 12.5 g in Potidea to 42.8 g in Antikythera. The prey formed only a minor part of this species’ diet. diversity ranged from 1.12 in Porto Lagos to 2.14 in In Porto Lagos small mammals were also the most Antikythera, while the evenness ranged from 0.11 in important prey (of at least five species, 97% by biomass). Evros Delta to 0.69 in Antikythera (Table 2). Owl diet in Greece 111 TABLE 2 diet by biomass, represented by only two species, namely Prey size and prey diversity indices of the four owl species in M. domesticus (15%) and C. suaveolens (7%). Greece The median prey biomass was significantly different between the five areas (Kruskall-Wallis test, x2 = 367.88, Aver- Me- Diver- Eve- N Min Max df = 4, p<0.001). Average prey biomass ranged from 0.7 age dian sity ness g on Tilos Island to 11.9 g in the Axios Delta. Prey diver- Tyto alba sity ranged from 1.15 on Tilos Island to 2.45 in Evros Evros 487 14.5 12.0 1.0 100 1.17 0.11 Delta, while the evenness ranged from 0.12 on Tilos to P. Lagos 116 17.2 20.0 2.0 20 1.12 0.17 0.58 in the Axios Delta (Table 2).