Herpersvirus strigis: host spectrum and distribution in infected owls.

Herpesvirus strigis, a new species of the genus Herpesvirus, is a pathogen for several species of owls in the order Srigiformes. Natural infection has been observed in the Eagle Owl (Bubo bubo L.), Long-eared Owl (Asio otus L.) and Snowy Owl (nyctea scandiaca L.) In addition the Little Owl (Athene noctua Scopolic) and Tengmalms Owl (Aegolius funereus L.) was experimentally infected. On the other hand the Tawny Owl (Strix aluco L.) and Barn Owl (Tyto albo Scopoli) proved resistant to a massive experimental infection. Of representatives from nine other orders of birds and mammals, only the Old World Kestrel (Falco tinnunculus L.) was found susceptible to this virus. Distribution of viral antigen in various organs of infected owls, as determined by immunofluorescence and by quantitative virus assay, was in accordance with the occurrence of macroscopic and microscopic lesions.     

乌鲁木齐市区越冬期长耳鸮的食性分析

2009～2011年间,利用食团分析法对乌鲁木齐市越冬长耳鸮(Asio otus)的食性进行分析。3年累计收集长耳鸮食团683份,辨认出1 132只猎物。分析结果表明,长耳鸮在冬季共捕食小型哺乳类6种,鸟类2种。小家鼠(Mus musculus)是最常见的食物,占总捕食量的53.45%。小型哺乳类是长耳鸮的主要食物,它在食物组成中出现的总频率为88.16%,以生物量计,小型哺乳类占食物构成的95.13%。长耳鸮的食物组成年度间差异显著,与当地猎物资源多样性和可获得性密切相关,表明长耳鸮可能采用机会主义者的捕食策略。     

Geographic and temporal variation in the consumption of bats by European Barn Owls

Capsule We report a review of the occurrence of bats in the Barn Owl diet Tyto alba in Europe. Based on 802 studies reporting 4.02 million prey items identified in pellets, 4949 were bats (0.12%). We found that bat predation decreased during the last 150 years, is more frequent on islands than mainland, and is higher in eastern than western Europe and in southern than northern Europe. Although Barn Owls usually capture bats opportunistically, they can sometimes specialize on them.     

Diet of the Long-eared Owl,Asio otus,in Central Anatolia (Aves: Strigidae)

In a one-year study on the diet of the Long-eared Owl, Asio otus, in the area of Karap?nar in Central Anatolia, 5324 prey items were recovered from 3314 pellets collected at monthly intervals. At least 7 species of mammals belonging to Insectivora (Crocidura suaveolens) and Rodentia (Allactaga williamsi, Cricetulus migratorius, Meriones tristrami, Mescocricetus brandti, Microtus guentheri, M. sp., Mus macedonicus) were identified. Rodentia were dominant and contributed 93.8% of the number of prey items of the Long-eared Owl. Microtus guentheri accounted for 83.9% of the rodent remains. The diet pattern was more diverse in summer, when some 24% of the diet consisted of non-mammal prey items (birds, insects).     

北京市区越冬长耳的食性分析

2004年11月至2005年4月,采用食团分析法对北京市区内天坛生物制药厂和国子监公园内栖息越冬的长耳鸮(Asiootus)的食物组成进行了分析。发现天坛生物制药厂长耳鸮的食物中啮齿类占41.0%,翼手类占29.5%,鸟类占29.3%,食虫类占0.2%;国子监长耳鸮的食物组成中翼手类占53.8%,啮齿类占21.5%,鸟类占24.7%。翼手目主要种类有山蝠(Nyctalus noctula)和普通伏翼(Pipistrellus abramus)等。长耳鸮三类主要食物所占比例的逐月变化显示,翼手类所占百分比不断上升,啮齿类所占比例先上升而到翌年1、2月开始下降,鸟类所占百分比一直在下降。蝙蝠大量出现于温带冬季鸮类的食物中属首次发现。     

Prevalence of Toxoplasma gondii in raptors from France

Little is known about the prevalence or importance of Toxoplasma gondii infections in raptors. Sera from Eurasian Buzzards (Buteo buteo, n=14), Tawny Owls (Strix aluco, n=12), Barn Owls (Tyto alba, n=18), Eurasian Sparrowhawk (Accipiter nisus, n=1), and Common Kestrels (Falco tinnunculus, n=8) were examined for agglutinating antibodies using the modified agglutination test at 1:25 dilution. Antibodies were not detected in Common Kestrels and the Eurasian Sparrowhawk but were detected in 11 Eurasian Buzzards (79%), six Tawny Owls (50%), and two Barn Owls (11%). Toxoplasma gondii, genotype II, was isolated from the brain of an adult Tawny Owl.     

Landscape and anti-predation determinants of nest-site selection, nest distribution and productivity in a Mediterranean population of Long-eared Owls Asio otus

Nest predation is an important determinant of owl breeding success. We studied Long-eared Owl Asio otus productivity and attributes of nest-sites at the microhabitat and landscape scales in a Mediterranean locality over an 8-year period. We examined the effect on nest location and productivity of protective cover in concealing the nest from aerial and terrestrial predators. A dense cover of ivy and tree-foliage at canopy level favoured nest location but not productivity. By contrast, high shrub cover beneath the nest was selected by Owls and was positively related to both the site reoccupancy rate and the overall number of young fledged. Pre-fledging Owls use the ground, where they are exposed to terrestrial predators, which are much more abundant in the study area than are aerial predators. Our results therefore support the hypothesis that Owls adapt nest-site choice to local sources of predation risk. As reported elsewhere, Long-eared Owls in our study area showed restricted territoriality and nested in clusters. As active nest-sites during the same breeding season were more than 1 km apart on average, and their productivity was never greater for clustered nests than for more isolated nests, nest aggregation could not be interpreted as a case of facultative colonial breeding, which has been reported for this species in other areas. Neither landscape variables indicative of the availability of foraging areas nor structural attributes that protect young from predators explained the remarkable scarcity of nests in half of the study area. Unmeasured factors such as human disturbance could explain the pattern of distribution of Long-eared Owl nests.     

Diet of a nesting pair of Long-eared Owls,Asio otus,in an urban environment in southwestern Turkey (Aves: Strigidae)

Pellets were collected under an active Long-eared Owl (Asio otus) nest in the city centre of Denizli, Turkey. The nest was located in a conifer tree in a 5.7 ha urban park, centrally-located in the city of Denizli, with a human population of 577,000 people. During April-June 2014, a total of 64 pellets containing remains of 86 individual prey items was found. All prey were Passeriformes and consisted of two species belonging to Passeridae and Hirundinidae. 78 of the 86 prey items (90.7%) were House Sparrow (Passer domesticus) and the other eight (9.3%) were House Martin (Delichon urbicum). This is one of the first studies to indicate that the Long-eared Owl's nesting season diet consists entirely of birds. The main factor affecting this result is probably the fact that the owls live in an urbanised setting.     

The decline of Common Kestrels Falco tinnunculus in a forested area of northern England: the role of predation by Northern Goshawks Accipiter gentilis

We have previously documented the decline of the Common Kestrel Falco tinnunculus over a 23‐year period in a large coniferous forest in northern England. Kestrels fed predominantly on Field Voles Microtus agrestis, which were most abundant in young plantations (1–11 years old). Over the 23 years, voles remained abundant in the study area, but their numbers fluctuated cyclically. Here we consider whether the decline of Kestrels was linked to predation by Northern Goshawk Accipiter gentilis. Goshawks first bred in the study area in 1973 and increased until 1989, after which numbers stabilized. We use a number of approaches to explore the role of Goshawk predation, all of which are correlative, but independent. First, there was a significant negative relationship between Kestrel and Goshawk numbers after controlling for a decline in vole habitat. Short‐eared Owls Asio flammeus, which also hunt by day, declined over the same period as Kestrels. Second, numbers of Tawny Owl Strix aluco and Long‐eared Owl Asio otus did not decline as Goshawk numbers increased. These two species are also vole‐dependent, but active by night, and less vulnerable to Goshawk attack. Third, six species of raptor comprised 4.5% of 5445 Goshawk prey items during the breeding season, but more Kestrels were killed than the combined total of all other raptors. Goshawks not only killed many adult Kestrels in early spring, prior to breeding, when it would have most impact on population levels, but there was also a temporal trend for predation on Kestrels to be inversely density‐dependent. Finally, we estimated that Goshawks removed more Kestrels than were recorded each spring in the study area. We interpreted this as indicating that immigrant Kestrels were being removed continually, mostly before they could breed. We conclude that the decline of Kestrels (and possibly Short‐eared Owls) was mainly due to predation by Goshawks. This study provides some of the strongest evidence yet of the role of predation in the hierarchical structuring of raptor communities.     

Within-season divorce in Common Terns Sterna hirundo in a year of heavy predation

Divorce between seasons is a common phenomenon in seabirds, whereas within-season mate change is rarely observed. We report four cases of within-season mate change in renesting Common Terns Sterna hirundo during a year of heavy predation by a Long-eared Owl Asio otus, when we found more deserted clutches, lower hatching success as well as more disappeared chicks compared to other years. Within-season nest-site fidelity also decreased under predation pressure.     

Fish in the diet of the Long-eared Owl Asio otus

Capsule: Analysis of regurgitated pellets showed that fish were a very rare prey in the diet of the Long-eared Owl Asio otus. Remains of 38 individual fish were found at 8 of 121 nests and only in 2 out of 11 years. Occurrence tended to be more frequent in warm dry periods, when water ditches were dry.     

Tawny Owl Strix aluco as an indicator of Barn Owl Tyto alba breeding biology and the effect of winter severity on Barn Owl reproduction

In the temperate zone, food availability and winter weather place serious constraints on European Barn Owl Tyto alba populations. Using data collected over 22 years in a Swiss population, we analysed the influence of early pre‐breeding food conditions and winter severity on between‐year variations in population size and reproductive performance. To estimate pre‐breeding food conditions, we attempted a novel approach based on an index that combines Tawny Owl Strix aluco reproductive parameters and the occurrence of wood mice Apodemus sp. in their diet. Tawny Owls breed earlier in the season than Barn Owls and are strongly dependent on the abundance of wood mice for breeding. This index was strongly positively associated with the number of breeding pairs and early breeding in the Barn Owl. Winter severity, measured by snow cover and low temperatures, had a pronounced negative influence on the size of the breeding population and clutch size. Food conditions early in the breeding season and winter severity differentially affect the Barn Owl life cycle. We were able to use aspects of the ecology and demography of the Tawny Owl as an indicator of the quality of the environment for a related species of similar ecology, in this case the Barn Owl.     

Brutbiologie und den Bestand steuernde Faktoren bei Waldkauz (Strix aluco) und Waldohreule (Asio otus) in der Schw?bischen Alb

Zusammenfassung Im Raum Göppingen—Geislingen—Laichingen wurden 126 Bruten des Waldkauzes und 80 Bruten der Waldohreule untersucht. Die Abhängigkeit von Brutbeginn, Gelegestärke, Jungenzahl, Verlusten und Bruterfolg von Höhenlage, Art des Nistplatzes, Witterung und Nahrungsangebot wird diskutiert und mit der Literatur aus anderen Gebieten verglichen. Der Waldkauz ist ausgesprochen ortstreu und durch große Anpassungsfähigkeit bei der Nistplatzwahl und Ernährung (Ausweichen auf Vogelnahrung in Mäuse-Mangeljahren) im Bestand und Bruterfolg relativ geringen Schwankungen unterworfen. Die Waldohreule ist mindestens in den Hochlagen der Schwäbischen Alb (hier 600–850 m ü. NN) Invasionsvogel mit sehr stark schwankendem Bestand und hoher Fortpflanzungsrate bei guter Witterung und Feldmausdichte. Hier zeigen sich deutliche Parallelen zu Untersuchungsergebnissen aus Skandinavien.

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Breeding biology and factors influencing density of the Tawny Owl(Strix aluco) and the Long-eared Owl(Asio otus) in the Schwäbische Alb (SW-Germany)

Summary Around Göppingen—Geislingen—Laichingen 126 broods of the Tawny Owl and 80 of the Long-eared Owl have been examined. Correlations between start of egg-laying, number of eggs and young, losses and breeding success to altitude, kind of nestsite, weather conditions and food are discussed and compared with results of other regions. The Tawny Owl always stays at the same place. There are relatively low changes in density and breeding success according to a high adaptibility concerning choice of nestsite and food (changing to birds in years with few voles). Long-eared Owls perform, at least in the high regions of the Schwäbische Alb (600–850 m), invasions causing highly variable densities. In good weather conditions and high density of field-voles the breeding success may be extraordinarily high. So parallels to the results from Scandinavia can be found.

     

Niche partitioning of avian predators in northern grasslands amended by biosolids

Many food webs are affected by bottom‐up nutrient addition, as additional biomass or productivity at a given trophic level can support more consumers. In turn, when prey are abundant, predators may converge on the same diets rather than partitioning food resources. Here, we examine the diets and habitat use of predatory and omnivorous birds in response to biosolids amendment of northern grasslands used as grazing range for cattle in British Columbia, Canada. From an ecosystem management perspective, we test whether dietary convergence occurred and whether birds preferentially used the pastures with biosolids. Biosolids treatments increased Orthoptera densities and our work occurred during a vole (Microtus spp.) population peak, so both types of prey were abundant. American Kestrels (Falco sparverius) consumed both small mammals and Orthoptera. Short‐eared Owls (Asio flammeus) and Long‐eared owls (Asio otus) primarily ate voles (>97% of biomass consumed) as did Northern Harriers (Circus hudsonius, 88% vole biomass). Despite high dietary overlap, these species had minimal spatial overlap, and Short‐eared Owls strongly preferred pastures amended with biosolids. Common Ravens (Corvus corax), Black‐billed Magpies (Pica hudsonia), and American Crows (Corvus brachyrhynchos) consumed Orthoptera, Coleoptera, vegetation, and only a few small mammals; crows avoided pastures with biosolids. Thus, when both insect and mammalian prey were abundant, corvids maintained omnivorous diets, whereas owls and Harriers specialized on voles. Spatial patterns were more complex, as birds were likely responding to prey abundance, vegetation structure, and other birds in this consumer guild.     

Strong decline in the consumption of invertebrates by Barn Owls from 1860 to 2012 in Europe

Capsule The analysis of 616 papers about the diet of the European Barn Owl Tyto alba showed that 9678 invertebrates were captured out of 3.13 million prey items (0.31%). The consumption of invertebrates strongly decreased between 1860 and 2012. This further demonstrates that the Barn Owl diet changed to a large extent during the last 150 years.     

Late Nest-Building of the Rook

While seasonal variation in the mammal prey of the Barn Owl may be influenced by changes in ground cover (as caused for example by haymaking), it seems to be primarily the result of normal annual fluctuations in the populations of the preferred prey species.     

Differential predation of eggs in clutches of Glaucous-winged Gulls Larus glaucescens

Differential predation of eggs of Glaucous-winged Gulls Larus glaucescens was studied on Mitlenatch Island, British Columbia. The predation of single eggs from 3-egg clutches by conspecifics and Northwestern Crows Corvus caurinus was recorded to assess whether the predators selected eggs at random or showed a preference for a specific egg in the laying sequence. It was found that small and light-coloured eggs, characteristically the last-laid egg in the clutch, were taken significantly more often than the other two eggs in the clutch. As chicks derived from this third egg are least likely to fledge because of their small size and the effects of asynchronous hatching, the lightness of the third egg is adaptive in that it helps to focus attention on the small egg.     

Extirpation of alternative prey during a small rodent crash

Summary We document two episodes, in different years, of Barn Owls (Tyto alba) preying on a winter population of Burrowing Owls (Athene cunicularia) on a southern California island. The predation in each case followed a marked shift in the diet of the Barn Owls, due to the cyclic decline of their normal small mammal prey. Heavy predation in the first year resulted in the extirpation of the Burrowing Owls on the island. Such heavy predation on alternative prey species is commonly reported in cyclic predator-prey systems, however this is the first documented case of extirpation of the alternative prey. Complete elimination of any prey species by terrestrial predators is, in fact, very rare.     

Flight performance, echolocation and foraging behaviour in noctule bats Nyctalus noctula

The noctule Nyctulus noctula (Schreber, 1774) is a relatively large (c. 25 g) insectivorous bat which catches insects on the wing (by aerial hawking). Emergence at a maternity roost was earliest relative to sunset when females were lactating, and bats may then have risked predation by flying at higher light levels during a period of high energy demand. Flight performance was quantified by using stereophotogrammetry. At feeding sites bats flew at 6.0 ± 2.1 m/s. This was faster than predicted minimum power speed (V _mp), and either between V _mp and maximum range speed (V _mr), or close to their predicted V _mr, depending on which aerodynamic model of flight power requirements was used. The echolocation behaviour of noctules is flexible. Long duration, low frequency calls (c. 20 kHz) with little frequency modulation were emitted while cruising, but at foraging sites the calls became more frequency-modulated. As the noctule is traditionally thought of as using low frequency echolocation, it was expected to receive weak echoes from small targets and therefore to specialize in eating large insect prey. Although the bats ate mainly beetles, large numbers of small dipterans were also eaten. The noctule is probably able to detect such small items because, when foraging, its calls become broadband and sweep from high frequencies. Higher harmonics are also present, and these may assist in the detection of small prey. In noctules, as in many bats, there appears to be a 1:1 link between wingbeat and call production during the search phase of foraging.     

Population increase of the Long-eared Owl,Asio otus (Linnaeus, 1758), in Iran (Aves: Strigidae)

The Long-eared Owl, Asio otus (Linnaeus, 1758), was known as a scarce wintering bird in Iran until 2010. There were altogether 25 records until the 1970s, but no data are available for the period between the 1970s and 1997. Between 1997 and 2014 there were at least 32 non-breeding and 17 breeding records available based on data of the Iran Bird Records Committee. Breeding was first confirmed in Nahavand (Hamedan Province) and has in the meantime been confirmed at 11 localities mainly in the western half of the country. The recent increase in records (from 25 records during 12 decades compared with 49 records during two decades) indicates that there has been a real increase in the numbers of Long-eared Owls occurring in Iran.