The Owl Pages

Winter Diet of Long-eared Owls Asio otus in Bergamo district

By Marco Mastrorilli

Introduction

In the present study of winter diet of Long eared owl in Lombardy (North of Italy) we found a significant presence of bird prey. The 671 pellets analysed yielded 867 prey of which 48% were of the Aves class (20 different species).

Pellets were collected in four roosts: two located in urban habitat (a cemetery and a private garden), and the other ones in the woods of Parco Adda Nord and Parco del Serio. In the two roosts of Bergamo and Caravaggio the percentage of birds was very high (55% and 51%) and it confirms expansion of Long eared Owls in northern Italy is in relation with colonisation of new areas (even degradated ones - record of Simpson index for Italy is 0.870973). One Athene noctua (cemetery of Caravaggio) was the only non Passeriformes we found.

In the pellets of Bergamo roosts I found a most important predation of Chiroptera (see Table 1) in Italy.

A small curiosity (look the slides) : in 3 pellets I found 3 Rings of birds : 2 Turdus merula and 1 Erithacus rubecola!

Data Tables and Photos

Roost 1 - Bergamo Town (North Italy)

Roost 2 - Cemetery of Caravaggio

Roost 3 - Trezzo, Parco Adda Nord woods

Roost 4 - Zanica, Parco del Serio


Bergamo Town (North Italy)

Foot of Turdus merula in Long-eared Owl pellet
1) foot of Turdus merula in Long-eared Owl pellet

Roost of Bergamo Town (North Italy) Table 1
N: number of prey B: biomass of prey

Species N N% B B%
Pipistrellus Kuhlii 17 12.4 170 4.9
Chiroptera 17 12.40% 170 4.90%
         
Microtus arvalis 1 0.72 27 0.782
Microtus subterraneus 1 0.72 20 0.579
Microtus Savii 3 2.17 54 1.56
Microtus spp. 2 1.44 42 1.21
Rattus norvegicus 1 0.72 100 2.89
Rattus rattus 2 1.44 200 5.79
Rattus spp. 3 2.17 300 8.69
Apodemus sylvaticus 17 12.31 357 10.3
Apodemus flavicollis 3 2.17 63 1.82
Apodemus spp. 3 2.17 63 1.82
Mus musculus 5 3.62 95 2.75
Muridae indet. 4 2.89 72 2.08
Rodentia 45 32.60% 1393 40.36%
         
Mammalia (mammals) 62 45% 1563 45.29%
         
Troglodytes trogl. 1 0.72 5 0.14
Erithacus rubecola 4 2.89 72 2.08
Turdus merula 5 3.62 450 13.03
Regulus regulus 5 3.62 25 0.72
Parus major 3 2.17 54 1.56
Parus indet. 2 1.44 36 1.043
Parus caerulus 4 2.89 52 1.506
Passer domesticae it. 19 13.76 532 15.41
Passer montanus 9 6.52 189 5.477
Fringilla coelebs 2 1.44 46 1.33
Carduelis carduelis 5 3.62 80 2.31
Carduelis chloris 1 0.72 27 0.78
Passeriformes indet. 16 11.5 320 9.27
Aves (Birds) 76 55% 1888 54.70%
         
Total prey 138 100% 3451 100%
Tarsus of Turdus merula with Ring found in Long-eared Owl Pellet
2) Tarsus of Turdus merula with ring

Caravaggio

pellet of Long eared owl
3) Pellet of Asio otus

Roost of Caravaggio Table 2
N: number of prey B: biomass of prey

Species n N% B B%
Crocidura russula 2 0.81 30 0.46
Crocidura Luecodon 5 2.02 50 0.77
Sorex araneus 2 0.81 20 0.31
Insectivora 9 3.66 100 1.55
         
Clethrionomys glaer. 5 2.02 105 1.63
Microtus arvalis 4 1.61 108 1.68
Microtus Savii 8 3.23 144 2.24
Microtus spp. 13 5.23 273 4.24
Rattus norvegicus 3 1.21 300 4.66
Rattus rattus 7 2.83 700 10.8
Rattus spp. 3 1.21 300 4.66
Apodemus sylvaticus 13 5.23 273 4.24
Apodemus spp. 10 4.04 210 3.26
Micromys minutus 12 4.85 84 1.3
Mus musculus 16 6.47 304 4.72
muridae spp. 19 7.69 342 5.32
Rodentia 113 45.7 3143 48.9
         
Mammalia (Mammals) 122 48.6% 3243 50.5
         
Athene noctua 1 0.405 150 2.3
Prunella modularis 3 1.21 54 0.84
Turdus merula 5 2.02 450 7
Turdus spp. 3 1.21 270 4.24
Erithacus rubecola 5 2.02 90 1.4
Parus caerelus 6 2.42 78 1.21
Parus major 7 2.83 126 1.96
Parus spp. 8 3.23 144 2.44
Passer domesticae it. 12 4.85 336 5.22
Passer montanus 7 2.83 147 2.28
Fringilla coelebs 4 1.61 92 1.43
carduelis chloris 7 2.83 189 2.94
Carduelis carduelis 18 7.28 288 4.48
Fringillidae spp. 12 4.85 192 2.98
Passeriformes indet. 29 11.7 580 9.02
Aves (Birds) 127 51.40% 3186 49.50%
         
Total prey 247 100% 6429 100%

Trezzo

Pellet of Asio otus with ring of Turdus merula
4) Pellet of Asio otus with ring of Turdus merula

Roost of Trezzo Table 3
N: number of prey B: biomass of prey

species N N% B B%
Muscardinus avellinarius 5 1.67 120 1.597
Clethrionomys glaerolus 9 3.01 189 2.51
Microtus savii 2 0.66 36 0.479
Microtus subterraneus 2 0.66 40 0.53
Microtus spp. 12 4.01 252 3.35
Apodemus sylvaticus 35 11.7 735 9.78
Apodemus spp. 22 7.35 462 6.15
Micromys minutus 15 5.01 105 1.39
Rattus norvegicus 2 0.66 200 2.66
Rattus rattus 7 2.34 700 9.31
Rattus spp. 3 1.003 300 3.99
Mus musculus 28 9.36 532 7.08
Muridae spp. 26 8.69 468 6.23
Mammalia (Mammals) 168 56.18% 4139 55.09%
         
Prunella modularis 1 0.33 18 0.23
Erithacus rubecola 9 3.01 162 2.15
Turdus merula 3 1.003 270 3.59
Turdus pilaris 1 0.33 85 1.31
Turdus spp. 2 0.66 170 2.26
Sylvia atricapilla 7 2.34 105 1.397
Parus major 4 1.337 72 0.95
Passer domesticus ital. 42 14.04 1176 15.6
Passer montanus 19 6.35 399 5.31
Fringilla coelebs 9 3.01 207 2.75
Carduelis chloris 9 3.01 243 3.23
Carduelis carduelis 6 2.006 96 1.27
Carduelis spinus 1 0.33 10 0.13
passeriformes indet. 18 6.02 360 4.79
Aves (Birds) 131 43.81% 3373 44.90%
         
Total prey 299 100% 7512 100%

Zanica

View of Zanica roost near the Serios river
5) View of Zanica roost near the Serio's river

Roost of Zanica Table 4
N: number of prey B: biomass of prey

species n n % B B%
Erithacus rubecola 4 2.18 72 1.25
Turdus merula 8 4.37 720 12.5
Parus major 1 0.54 18 0.31
Sturnus vulgaris 13 7.1 910 15.90%
Passer domesticus it 15 8.19 420 7.34
Passer montanus 4 2.18 84 1.46
Fringilla coelebs 3 1.639 69 1.2
Serinus serinus 3 1.639 45 0.78
Carduelis chloris 7 3.82 189 3.3
Carduelis carduelis 4 2.18 64 1.11
Aves indet. 15 8.19 300 5.2
Aves 77 42% 2891 50.50%
         
Crocidura leucodon 2 1.09 20 0.349
Muscardinus avellinarius 2 1.09 48 0.83
Clethrionomys glaerolus 1 0.54 21 0.36
Microtus arvalis 2 1.09 54 0.94
Microtus Savii 7 3.82 126 2.204
Microtus spp. 8 4.37 168 2.939
Apodemus sylvat. 15 8.19 315 5.51
Apodemus spp. 18 9.8 378 6.61
Micromys minutus 6 3.279 42 0.73
Rattus norvegicus 3 1.639 300 5.2
Rattus rattus 2 1.09 200 3.499
Rattus spp. 5 2.73 500 8.7
Mus musculus 22 12.02 418 7.31
Muridae spp. 13 7.103 234 4.09
Mammalia 106 58% 2824 49.50%
         
Total prey 183 100% 5715 100%

Acknowledgements

Special Thanks to Anna Barbagallo and Enrico Bassi for this study and Tea Sala, Davide De Vecchi, Francesca Galizzi for your help on field.

And special thanks to Claudia Savio for your help in translate and Gianna Dondini and Simone Vergari (Natural Hist. Museum of Florence) and Paolo Gaelotti (University of Pavia, Dept. Of Animal Biology) for your help.

References:
Mastrorilli M., Barbagallo A., Bassi E., 1999 - Dati sulla nicchia trofica invernale del Gufo comune Asio otus in provincia di Bergamo 10° Italian National Conference of Ornitology Caorle (Venice) ITALY - Avocetta Italian Journ.of Ornit. 23:54

Page last updated 2000-08-10