Diet Of Barn Owl Research Articles

Dietary Trends of Barn Owls in an Agricultural Ecosystem in Northern Utah

Abstract Barn Owl (Tyto alba) diets were studied for 15 years in Utah. Ninety-eight percent of 111,016 prey items were mammals, heavily dominated by voles (Microtus spp.). Food-niche breadth (FNB) was 3.33 for the entire sample and varied gradually but significantly among the 15 years and among seasons. Frequency of prey in the diet did not vary significantly from year to year or among seasons. Mean daily temperatures did not vary significantly among years but annual precipitation totals and days when deep snow covered the ground varied significantly among years. Irrigation for agriculture may have partially mitigated annual precipitation fluctuations. Hay, one of the most important crops on the study area, increased over the study period and other crops decreased slightly in the amount planted. Hectares of hay planted, hectares of corn planted, and hectares of barley planted were the variables that combined to best predict annual FNB.

Diets of Barn Owls Differ in the Same Agricultural Region

Abstract We studied the diet of 20 Barn Owl (Tyto alba) pairs breeding in three habitats (alfalfa fields, date plantations, and villages) in the same agricultural region in the Jordan Valley, Israel. Small mammals, particularly three rodents (Levant voles [Microtus socialis guentheri], house mouse [Mus sp.], and Tristram's jird [Meriones tristrami tristrami]), comprised 73 to 88% of the 3,544 prey items taken by Barn Owls in the three habitats. Frequencies in number and biomass of the rodent species differed among habitats. The number of bird species, their frequencies, and biomass in the diet were higher in villages than in the other two habitats, and were related to the higher diversity of birds breeding in villages. The frequency of birds in the diet was negatively correlated with distance from the village to open fields. Differences in the diet of Barn Owls among the three habitats most likely reflected differences in the distribution and abundance of the prey items in each habitat.

Diet of Barn Owls (Tyto alba) in Northern Belize

Diet of the barn owl (Tyto alba) has been well studied in temperate regions of the world, but there is a notable paucity of dietary data from the Neotropics. In this study, we examined diet of barn owls at Gold Button Lagoon in northern Belize. Pellets and prey remains were collected at roosting sites during 1997–1998. Diet was composed primarily of small mammals. Sigmodon hispidus was the most common prey in terms of frequency of occurrence and biomass, with lesser numbers of other rodents being consumed. Similar to other reports for the Neotropics, barn owls in our study consumed relatively larger prey than conspecifics inhabiting temperate regions. Birds and amphibians were a minor component of diet.

Food of the Barn Owl (Tyto alba) in the Eastern Mediterranean

Food of the Barn Owl (Tyto alba) in the Eastern Mediterranean The composition of the Barn Owl (Tyto alba) diet analysed from pellets collected in several regions of the Eastern Mediterranean is presented. In total, 27 samples from 21 sites in S Italy, S Greece (incl. Crete), S Turkey, NW Syria, SW Lebanon, N Israel, and N Egypt were composed of 8842 prey individuals. Mammals represented the dominant part of the prey (90% of the identified prey individuals, comprising 44 species). Birds were less abundant (7%), however, their diversity was enormous (64 species). Amphibians and reptiles were rarely represented in the diet (0.9%), while invertebrates we found more often (2.2%). The relative abundance of particular prey items in the Barn Owl diet was analysed in four geographical regions: (a) SE Europe (Calabria, Peloponnese, Crete), (b) Levantine parts of Turkey and Syria, (c) Lebanon and N Israel, and (d) N Egypt. In complex evaluation of the sample set, endemic forms composed a special group of prey items: Microtus savii, Sorex samniticus, and Talpa romana in Calabria; Microtus thomasi in Peloponnese; Acomys minous in Crete; and Gerbillus amoenus in Egypt. Another group of prey is represented by typical Levantine species: Microtus guentheri, Meriones tristrami, Apodemus mystacinus, and Rana ridibunda. Apodemus flavicollis and Crocidura leucodon were more abundant in Calabria while less abundant in the Levant. Synanthropic mammals (Mus spp., Rattus rattus, Suncus etruscus, Crocidura suaveolens) and birds (Passer domesticus) represented a significant part of the diet in the majority of the studied area.

Small Mammal Prey Selection by Two Owl Species in Southeastern Brazil

A variety of factors influence prey selection by predators. Because Barn Owls (Tyto alba) and Burrowing Owls (Athene cunicularia) differ in size and foraging tactics, we expected differential predation on small mammal prey. We hypothesized that the Barn Owl, an active predator, would prey on smaller and younger individuals than the Burrowing Owl, a sit-and-wait predator. We used pellet analyses to evaluate selection of small mammals by the two owls in relation to prey species, age, and size at the Ecological Station of Itirapina, state of Sao Paulo, in southeastern Brazil. Small mammals constituted most of the prey individuals and biomass in the diet of Barn Owls. Although Burrowing Owls consumed a wider range of taxa, small mammals represented one-third of all biomass consumed. With respect to small mammals, Barn Owls foraged selectively relative to prey species, size, and age. Burrowing Owls foraged opportunistically relative to prey species, but selectively relative to prey size and age. Barn Owls selected smaller and younger (juvenile and subadult) individuals of the delicate vesper mouse (Calomys tener) and Burrowing Owls preyed more on larger and older (subadult only) individuals. Morphology and behavior of both prey and predators may explain this differential predation. Our data suggest that the active predator feeds on smaller and younger prey and the sit-and-wait predator took relatively larger and older prey.

Habitat associations of small mammals in southern Brazil and use of regurgitated pellets of birds of prey for inventorying a local fauna

We inventoried terrestrial small mammals in an agricultural area in southern Brazil by using trapping and prey consumed by Barn Owls (Tyto alba) and White-tailed Kites (Elanus leucurus). Small mammals were trapped in three habitat types: corn fields, uncultivated fields ("capoeiras"), and native forest fragments. A total of 1,975 small mammal specimens were trapped, another 2,062 identified from the diet of Barn Owls, and 2,066 from the diet of White-tailed Kites. Both trapping and prey in the predators' diet yielded 18 small mammal species: three marsupials (Didelphis albiventris, Gracilinanus agilis, and Monodelphis dimidiata) and 15 rodents (Akodon paranaensis, Bruceppatersonius iheringi, Calomys sp., Cavia aperea, Euryzygomatomys spinosus, Holochilus brasiliensis, Mus musculus, Necromys lasiurus, Nectomys squamipes, Oligoryzomys nigripes, Oryzomys angouya, Oxymycterus sp.1, Oxymycterus sp.2, Rattus norvegicus, and Rattus rattus (Linnaeus, 1758)). The greatest richness was found in the uncultivated habitat. We concluded that the three methods studied for inventorying small mammals (prey in the diet of Barn Owls, White-tailed Kites, and trapping) were complementary, since together, rather than separately, they produced a better picture of local richness.

Locality Related Changes in the Diet of the Barn Owl (Tyto alba stertens) in Agroecosystems in Central Punjab, Pakistan

Abstract We studied spatial differences in Barn Owl (Tyto alba stertens) diets in agroecosystems of six districts of central Punjab, Pakistan. Analysis of pellets collected over 3 years revealed the house shrew (Suncus murinus) dominated all diets. This species constituted 75.0% of the diet in the Sheikhupura District, 68.4% in the Okara District, 67.2% in the Faisalabad District, 65.6% in the Toba Tek Singh District, 59.3% in the Jhang District, and 56.3% in the Hafizabad District. Rats and mice together formed 28% of the overall diet while birds (4.2%) were consumed more than bats (2.0%). The greatest diversity in Barn Owl diets was in the Jhang District.

ENDEMIC AND INTRODUCED VERTEBRATES IN THE DIET OF THE BARN OWL (TYTO ALBA) ON TWO ISLANDS IN THE GULF OF CALIFORNIA, MEXICO

Through the analysis of 458 barn owl (Tyto alba) pellets collected between 1981 and 1995 on 2 islands in the northern Gulf of California, Mexico, we found significant differences in the main components of the diet of barn owls on these islands, where introduced rodents, bats, and seabirds occur. On Rasa Island, the most important prey was Rattus rattus, followed by Myotis vivesi, Oceanodroma microsoma, Mus musculus, and 4 bird species. On Partida Island, the main prey was M. vivesi, followed by O. microsoma, R. rattus, and 3 bird species. The mean number of prey per pellet was higher on Partida Island (1.08) than on Rasa Island (0.91), but the mean biomass per pellet was higher on Rasa Island (75.8 g) than on Partida Island (25.8 g). The storm-petrels O. microsoma and O. melania were taken by barn owls in proportion to their abundance on both islands. Conversely, barn owls on Rasa Island ate more R. rattus than M. musculus, possibly because of the larger size of the former. Overall, our data suggest that barn owls in the Gulf of California behave as flexible predators that take prey according to availability and profitability.

NESTING AND DIET OF THE BARN OWL (TYTO ALBA) IN PAKISTAN

ABSTRACT We investigated nesting of Barn Owls (Tyto alba) in central Punjab, Pakistan, from 1999–2002. We also documented diet of Barn Owls in southern Punjab and southeastern Baluchistan, Pakistan. Of 40 nests found in central Punjab, 33 were located in tree hollows, four in buildings, and three in nest boxes. Egg-laying was observed primarily between the second week of August and October (N = 23), with a smaller number of nests started May–July (N = 5). Fledging of the autumn nests was completed by early January, and all breeding efforts observed in May–July were unsuccessful. During the August–January breeding period, clutch size averaged 5.83 eggs (SE = 0.47; range = 1–12; N = 23) and brood size 4.15 nestlings (SE = 0.28; range = 2–7; N = 20). Shrews (59%), birds (19%), rats and mice (13%), and insects (7%) were the main prey in southern Punjab, whereas rats and mice (93%), shrews (4%), and amphibians and reptiles (3%) were the main prey in southeastern Baluchistan.

Food partitioning between breeding White-tailed Kites (Elanus leucurus; Aves; Accipitridae) and Barn Owls (Tyto alba; Aves; Tytonidae) in southern Brazil

I examined the diet of breeding White-tailed Kites (Elanus leucurus; Aves; Accipitridae) and Barn Owls (Tyto alba; Aves; Tytonidae) in an agrarian area of southern Brazil by analyzing regurgitated prey remains. The objective was to evaluate how these raptors, which differ markedly in their hunting activity periods (owls are nocturnal and kites diurnal), share their mammalian food component. 2,087 prey consumed by Barn Owls and 1,276 by White-tailed Kites were identified. They presented a high overlap of food-niches (Piankas index was 0.98). Based on the daily activity period of their main small mammal prey, a lower overlap would be expected. The crepuscular/nocturnal Mus musculus was the main prey for the diet of breeding Barn Owls (81%) and White-tailed Kites (63%). This small exotic rodent provided 63% of the small mammal biomass ingested by owls and 44% by kites. Larger native small mammals were also considered important for the diet of kites, mainly because of their biomass contribution. Although these raptors differ markedly in their hunting activity periods, Barn Owls and White-tailed Kites are very similar predators in southern Brazil, overlapping their diets.

The Effects of Land-use and Landscape Structure on Barn Owl (Tyto alba) Breeding Success in Southern England, U.K.

To aid effective conservation and management there is a need to understand the effect of landscape on species ecology. The aim of this research was to assess the effect of landscape parameters on breeding success of barn owls throughout the Rother and Arun River catchments, Sussex, UK. We used a Geographic Information System to describe the habitat mosaic and landscape structure within an estimated home range area of 3 km2 around 85 artificial nest box sites. Results showed that land cover was less heterogeneous at successful sites, with home ranges dominated by a few habitat types of regular patch shapes. Unsuccessful nesting sites had significantly more improved grassland, suburban land and wetlands than successful sites. Cluster analysis and Principle Components Analysis was used to assess the similarity of the habitat mosaic within these areas and pellet analysis was undertaken to assess barn owl diet and prey availability. Ten prey species were recovered from pellets, field vole (Microtus agrestis), common shrews (Sorex araneus) and house mice (Mus musculus) making up nearly 90% of recoveries. However box sites varied in relative proportions of small mammal, and hence prey availability. Results indicated that land use and landscape structure can affect breeding success in barn owls. Higher levels of poor quality small mammal habitat were associated with unsuccessful sites. However, at a landscape scale, the habitat mosaic across the study area lacked variation, limiting analysis and clear correlations between habitat type and positive breeding success, suggesting that a finer scale was needed in future studies utilising this approach.

Occurrence and diet of a Barn Owl (Tyto alba) in the sub‐Antarctic

A Barn Owl Tyto alba was recorded at Grytviken, South Georgia (54°15′S, 36°45′W), in the South Atlantic during 1997 and 1998. Although Barn Owls are known to breed on the Falkland Islands (52°S, 58°W), this is the first known record of this species in the sub-Antarctic. In the 1997 austral winter a bird was found roosting in an old freezer plant in the abandoned whaling station at Grytviken. There were no sightings during the summer but a bird was again seen regularly from 13 July 1998 until 6 October 1998. Pellets were collected from the roost site from 30 August to 6 October 1998. After this date there were no fresh pellets and no subsequent sightings. A total of 19 intact pellets was examined and found to contain the skulls, bones and fur of the Common Rat Rattus norvegicus. Nine of these pellets contained single intact skulls, along with skeletal remains. Skulls were absent from the remaining 10 but most contained a set of rat limb bones. A further group of pellets that had become partially decomposed and therefore could not be separated into individual pellets contained a total of seven intact skulls. The body mass of rats taken was estimated from the length of the left jaw (Morris 1979). The mean jaw length was 22.3 mm (se = ±0.26 range 20.3–24.7) which gave an estimated body mass of 119 g (se = ±6 range 75–189 g). The origin of the Barn Owl was unknown. However, the nearest breeding site of the subspecies T. a. tuidara is in the Falkland Islands, 1400 km away (Woods & Woods 1997). Barn Owls have occasionally been recorded travelling large distances. A bird ringed as a nestling in New Jersey in 1981 was recovered in Bermuda 20 months later, a cross water journey of 1250 km (Soucy 1985). It is possible that migrations of this distance are aided by ship travel. Mueller and Berger (1959) reported a Barn Owl that had been ringed as an adult in Wisconsin and captured on a ship 360 km east of Savanna, Georgia, USA. Previous reports show that birds have travelled to South Georgia onboard ships. Examples of these include a Peregrine Falcon Falco peregrinus that came aboard a ship and flew ashore on South Georgia in 1986 and 26 Cattle Egrets Bubulcus ibis in 1993 that joined the RV Nathanial Palmer half way between the Falkland Islands and South Georgia and flew ashore at Stromness (Prince & Croxall 1996). It therefore seems likely that a species such as a Barn Owl travelled in a similar way and it may be no coincidence that Grytviken is the most frequently visited location by tour ships and fishing vessels on South Georgia. The survival of the Barn Owl in sub-Antarctic conditions was possible because of suitable roost sites provided by the disused whaling station and an abundant food supply of rats that were introduced by sealers and whalers in the 1800s (Pye & Bonner 1980). The only other introduced rodent present on South Georgia is the House Mouse Mus musculus that was found to occur in an isolated population at Queen Maud Bay more than 60 km from Grytviken (Berry et al. 1979). Rats are found in the diet of Barn Owls throughout the world (Taylor 1994). Because of their size rats provide a considerable energy source and it would appear that this allowed either one individual to survive for more than a year or two birds for several months. However, Barn Owls appear to be poorly adapted to low temperatures, high wind speeds and prolonged snow cover (Taylor 1994). The Barn Owl may have the ability to colonize new areas by long-distance displacements of far-ranging birds. However, the disappearance of this individual(s) suggested that the present climatic conditions of the sub-Antarctic were too extreme for long-term survival.

Relative importance of plague rodents and dasyurids as prey of barn owls in central Australia

We examined the diet of the barn owl in three bioregions of arid Northern Territory; two in upland areas, the other on the Barkly Tableland. Owls from the MacDonnell and Petermann Ranges fed predominantly on rodents. At both sites, Mus musculus was the dominant prey both in terms of frequency and prey units, with Pseudomys hermannsburgensis an important secondary item. Notomys alexis was an important secondary item in the MacDonnell Ranges. These results support previous research in highlighting the importance of plague rodents in the diet of barn owls in arid Australia. In contrast to the samples from the upland sites, the Barkly Tableland sample was composed mostly of the dasyurid marsupial Sminthopsis macroura, with only one rodent captured. The absence of the long-haired rat, Rattus villosissimus, from the sample, despite the species being a favoured prey item of the barn owl that undergoes population irruptions at the collection site, suggests that the sample was collected during a non-plague period. Our study is the first to record a marsupial species as the major prey of the barn owl. This finding suggests that barn owls can switch to other prey when populations of rodents crash.

Changes in the food of British Barn Owls (Tyto alba) between 1974 and 1997

ABSTRACTComparison of the results of a 1993–97 Barn Owl Tyto alba pellet survey with those of a similar survey from 1956–74 showed that Barn Owl diet had changed significantly. The primary differences were a widespread decrease in the percentage of Common Shrew Sorex araneus, combined with an increase in Pygmy Shrew Sorex minutus. The percentage of Wood and Yellow‐necked mice Apodemus sylvaticus and A. flavicollis and Bank Vole Clethrionomys glareolus in the diet also increased. Changes in Barn Owl diet since 1974 were independent of land‐class group, but were dependent upon region. This was due primarily to a large increase in the percentage of Apodemus spp. in Eastern England. Whilst the percentage of Pygmy Shrew in Barn Owl diet showed significant regional variation, there was no significant variation between land‐class groups. The diversity of Barn Owl diet increased between 1974 and 1997, although it was still lower in 1997 than earlier in the century. This increase was dependent upon region, but independent of land‐class group. The combined results of both surveys showed significant interland‐class group variation in dietary diversity. Changes in diet are discussed in relation to the intensification of agriculture and other changes in land management since the 1970s. The effects on Barn Owls of these changes in prey abundance are discussed, particularly in relation to the decline in Barn Owl numbers during the twentieth century.

Trophic niche of the barn owl and little owl in a rice field habitat in northern Italy

We characterized the trophic niche of two syntopic owl species, barn owl (Tyto alba) and little owl (Athene noctua), which inhabit rice field and water‐meadow habitats of northern Italy. Small mammals were the most important prey category for barn owls with 84% of prey, while invertebrates (primarily insects) accounted for approximately 55% of little owl prey. Small mammals were the staple food of both predators in terms of relative biomass of prey. Barn owls preyed upon larger rodent species (common rats, water voles), whereas little owls concentrated their hunting pressure on wood mice, a medium‐sized rodent. Mean weight of small mammals ingested by barn owls (37.7 g) was considerably greater than that by little owls (22.3 g). Dietary width was significantly greater in little owl than barn owl diet (2.2 vs 1.4), although the reverse was true for that of width in relation to small mammal prey (8.5 for barn owls vs 4.7 for little owls). Niche overlap was considerably high (GO = 0.94), but not complete.

Monitoring the Exposure of Barn Owls to Second-Generation Rodenticides in Southern Eire

In an extensive field study conducted over five counties in southern Eire during the winter of 1988–89, 19 Barn Owl (Tyto alba) roosts and/or nests were located. The local farmers and landowners within about a one-mile radius of the Barn Owl sites were surveyed concerning their use of rodenticides and observations of any secondary rodenticide toxicity effects. Regurgitated owl pellets were collected: (a) for dissection and prey analysis, and (b) for chemical analysis to determine residues of the second-generation rodenticides, brodifacoum, difenacoum and flocoumafen. Most farmers interviewed used rodenticide baits (73%), and almost all (92%) stated that they took precautions to protect domestic and wild non-target animals. The four rodent species, brown rat, wood mouse, house mouse and bank vole provided 83% of the Barn Owl diet, and birds contributed another 12%. At least 97% of the 89 pellets analysed contained less than the limit of determination of the three second-generation rodenticides, 0·01–0·02 mg kg−1 of each isomer. Apparent residues in the remainder were likely to be the result of interference from co-extracted material. These results indicated that during the monitoring period, none of the owls studied was exposed to significant residues of these rodenticides in their prey.

Diet and Nesting Success of Barn Owls Breeding in Western Nebraska

-We analyzed the diet of barn owls (Tyto alba) in Lincoln County, Nebraska during nesting seasons of 1984 through 1986 and their nest success in 1985 and 1986. Nesting attempts were made at 9 of 13 nest sites checked in 1985 and at 12 of 15 nest sites in 1986. Microtus ochrogaster comprised 32.7% of 10,140 prey items overall with marked increase in percent from 1985 to 1986. Barn own reproduction increased from 1985 to 1986 with more nests initiated, a higher proportion of successful nests and higher mean number of young fledged per nest attempt. Proportions of prey in the diet were significantly different from proportions of prey captured by trapping. Microtus ochrogaster was overrepresented and Peromyscus maniculatus underrepresented in the diet. Annual percentages of M. ochrogaster and Perognathus hispidus in the diet were negatively correlated with Reithrodontomys megalotis and with P. maniculatus but were not correlated with each other. Reithrodontomys megalotis and P. maniculatus were not correlated with each other. Reithrodontomys megalotis decreased and P. hispidus increased in the diet each year. A number of factors influence barn owl reproductive success including diet, quality of nest site and foraging ability of

Trends in North American small mammals found in common barn-owl (Tyto alba) dietary studies

Data on mammals were compiled from published studies of common barn-owl (Tyto alba) pellets. Mammalian composition of pellet samples was analyzed within geographic regions in regard to year, mean annual precipitation, latitude, and number of individual mammals in the sample. Percentages of individuals in pellets that were shrews increased whereas the percentages of rodents decreased with greater mean annual precipitation, especially in northern and western areas of North America. From the 1920s through 1980s, in northern and eastern areas the percentage of species that was shrews decreased, and in northern and central areas the percentage of individuals that was murid rats and mice increased. Human alterations of habitats during these seven decades are postulated to have caused changes in available small mammals, leading to changes in the barn-owl diet.

The diet of barn owls at a roost near Grahamstown

Barn owl Tyto alba pellets were collected over a period of 13 months from a roost near Grahamstown. Twelve species of small mammals and two bird species were found in the pellets. Mastomys natalensis and Mus minutoides were most numerous in the diet of the owls toward the end of winter whilst in summer Otomys irroratus and O. saundersae formed most of the prey remains.

Per una biogeografia dei sistemi trofici: il sistema "mammiferi terragnoli - Tyto alba" nell'Italia peninsulare e nelle isole maggiori

B/OGEOGRAPHIA — vol. XI - 1985 Principi e rnetodi deII’anaIisi biogeografica Per una biogeografia dei sistemi trofici: il sistema «mammiferi terragnoli - Tyzfo czlba» nell’Italia peninsulare e nelle isole maggiori(qq‘) LONGINO CONTOLI (**), MARIA PIA SALUCCI (qqq') e AUGUSTO VIGNA TAGLIANTI (’”qq*) (qqq) Centro per la Genetica Ev0luzz'om'stz'ca, C.N.R., Via Lamcz'sz', 29 - 00161 Roma (*’qq*) Via Isole Eolie, 7 - 00141 Roma (’““qq‘) Dz'partz'mem‘o dz’ Biologic: Animale e dell’Uomo (Zoologia), Universz'tci di Roma «La Sapienza», Viale dell’Um'versz'tci, 32 — 00185 Roma SUMMARY Towards a biogeogmp/7y of trophic systems: the «terrestrial mammals - Barn Owl» systems in peninsular Italy and main islands. This work is aimed at the comparative evaluation of the role of historical versus ecological factors in outlining the regional features of trophic systems «terrestrial mammals - Tyto alba». The studied area is peninsular Italy and Corsica, Elba, Malta archipelago, Sardinia and Sicily islands. In such a perspective, we made a comparison between the above trophic qualitative patterns and faunistic ones, resulting from general faunistic knowledges on the small mammals. Among the above areas, two highly homogeneous clusters appear: the bigger one referring to the peninsular regions, exclusive of Apulia (expecially with respect to Barn Owl diets) and, even if to a lesser extent, of Eastern Liguria, the smaller one referring to the lesser islands. Sardinia is quite related to Sicily with respect to diets (perhaps due to vegetation being historically influenced in a similar way by human impact) and to smaller islands with respect to faunistic patterns, possibly heavily linked to man’s colo- nization and cultural flows. In general, the difference between the islands and peninsular Italy is much greater in faunistical comparisons than in trophic ones. Concerning the preyed mammalian taxa, the following groups (chorotypes) emerge: a) 4 entities widespread both in peninsula and in islands (Suncus etruscus, Apodemus (Sylvaemus) sp., Rattus rattus, Mus domesticus). With respect to trophic comparison, this group includes also Crocidura suaveolens; b) 7 entities everywhere present in peninsular Italy, but lacking from the islands (Sorex anmeus vel samniticus, Sorex minutus, Neomys cmomalus, Crocidura Zeucodon, Muscardinus auellamzrius, Arvicola ter- restris, Microlus (Pitymys) saviz); c) 2 «mesophilous» species bounded to the Po valley (Microtus arvalzs and Micromys minutus); cl) Microtus (Pitymys) multiplex, found in Apuane Alps; e) Crocidura russula, of Sicily, Sardinia and Maltese islands; f) Tzzlpa romamz, lacking from the northern part of peninsular Italy. The main difference between trophic and faunistic approaches are linked to the following species, all quite insulated as trophic components, due to their scarcity in Barn Owl diet: — Eliomys quercinus and Rattus norvegicus, linked to the «a» faunistic group; — Neomys fodiens and perhaps Cletbrionomys glareolus, linked to the «b» faunistic group. The patterns of the above species and of those of the «a» group seems to be related mainly to ecological factors; the other patterns are mainly due to historical factors. The overall overlap of trophic v.s faunistic spectra seems smaller in southern regions of peninsula and in Sicily. Trophic systems can establish themselves in a given area only if the habitat dimensions of ecological (*) Ricerche parzialmente eseguite con il contributo del C.N.R. (Gruppo Nazionale Biologia Naturali- stica, ctb. 85.00828.04) 211