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Four generally recognized morphotypes found in south-European Ural Owl (Strix uralensis macroura) population: (a) pale morph, (b) grey morph, (c) partly melanistic morph and (d) melanistic morph. Drawings by Žarko Vrezec.
Source publication
In Slovenia the Ural Owl (Strix uralensis) is on its south-western limit of distribution and belongs to the southern subspecies Strix uralensis macroura. Dark coloured owls are characteristic for this subspecies and represent between 5 to 15% of the population. Slovenian breeding population size is estimated at 400 to 700 pairs. The densities of te...
Context in source publication
Context 1
... frequency of melanism in South- European population of Ural Owl is quite high, and has paid a lot of attention in the past (Ponebšek, 1917;Kohl, 1977;Vrezec, Tutiš, 2003;Vrezec 2009). In order to as- sess frequency of generally four colour mor- photypes in Ural Owl population in Slovenia described so far ( fig. 2; Vrezec, 2009), we have collected the following types of data into the study in order to get more or less unbiased sample: (1) museum skins (only birds that were found dead in the field), (2) data from breeding biology studies in the field (predominantly from nestboxes), and (3) photographs taken in the wild with lo- cation details ...
Citations
... It seems that, in temperate mixed forests, the Ural Owl cannot find sufficient alternative prey to compensate for a shortage in the main prey (voles and mice). In boreal and hemi-boreal forests, Ural Owls can take a larger proportion of birds in low vole years, but this is not the case in temperate forests, not even in the non-breeding period (Vrezec 2016. We suggest that in temperate forests, Ural Owls are more specialized on mice and voles, with dormice as an alternative prey being large, easy to catch and profitable . ...
Montane temperate forests in Central and Southern Europe host diverse small mammal assemblages, but the fluctuations in these assemblages in correlation with owl predators are still poorly explored. The key questions of our study were how coexisting owls responded to different prey fluctuations and whether any particular small mammal species governed predator-prey co-dynamics. We conducted a long-term study (2004 – 2020) in low-elevation (300-1100 m asl) mixed Beech and Silver Fir forest in the northern Dinaric Alps (central Slovenia). Monitoring data on the main small mammal groups, i.e. mice Muridae, voles Cricetidae, dormice Gliridae and shrews Soricidae, and three owl species, i.e. the Ural Strix uralensis, Tawny Strix aluco and Boreal Owl Aegolius funereus, were collected annually. To find relationships between prey and predator populations, we used two types of supervised machine learning approaches and addressed three predictive modeling tasks of multi-target regression. The dominant species in the small mammal assemblage, the Yellow-necked Mouse Apodemus flavicollis, had a key role in determining predator populations and their breeding performance. We noted higher sensitivity to small mammal fluctuations in boreal zone owl species (Boreal and Ural Owl), which reach their southern distribution limit in the Dinaric Alps, while the temperate zone species (Tawny Owl) seemed to be less affected. In years of prey-shortage, the Boreal Owl was found to presumably abandon its territories, the Ural Owl suppressed breeding and the Tawny Owl sustained breeding activity by shifting prey selection. Low-elevation forests appeared to be suboptimal habitat for the competitive subordinate Boreal Owl, which may exploit occasional outbreaks of small mammal populations in these habitats even in the presence of larger competitors. Whether low-elevation forests can play a role in maintaining threatened and cold-adapted Boreal Owl in central and Southern Europe in the face of recent ecosystem changes due to climate and environmental changes, remains an open scientific question.
... In all parts of the range, voles Cricetidae predominate in the diet, on average forming around 60% of all prey items (Mikkola 1983, Jäderholm 1987, Korpimäki & Sulkava 1987, Korpimäki et al. 1990, Czuchnowski 1997, Sidorovich et al. 2003, Shokhrin 2009, Kociuba 2012. This proportion decreases towards the southern part of the range in Central Europe and Japan, however, where higher proportions of mice Muridae in the diet were reported (Stürzer 1998, Obuch et al. 2013, Suzuki et al. 2013, Vrezec 2016. In some studies shrews Soricidae have also been reported in higher proportions, but never exceeding 20% of the prey items (Korpimäki & Sulkava 1987, Stürzer 1998. ...
... For example, in the areas where large and profitable prey are available only for a limited time of the season (e.g. Fat Dormice in Beech temperate forests), large shifts in the diets of Ural Owls and other coexisting large predators have been recorded (Krofel et al. 2011, Vrezec 2016 leading to an overall increase in the diversity of prey taken. The latter corresponds well with the prey availability hypothesis, in which high availability of profitable prey may lead to increased reproductive success because of enhanced opportunities for profitable prey captures (Whitfield et al. 2009). ...
Capsule: Voles are the main prey of the Ural Owl Strix uralensis in Europe, with larger prey and higher prey diversity being positively associated with owl breeding performance.
Aims: To assess the breeding diet and its influence on the breeding performance of the Ural Owl across a north–south gradient of its European range using nest box monitoring data.
Methods: Comparable monitoring of nest boxes in different biogeographical regions of Europe (Finland, Latvia, Slovenia) and diet analysis from nest samples to assess the taxonomic and trait influence of prey on owl breeding performance in different environments.
Results: High plasticity in the Ural Owl hunting behaviour under different prey availability conditions resulted in significant differences between regions and years. Voles formed the highest proportion of the diet in all studied regions. Owl brood size was positively associated by higher proportions of voles and mice in the diet, and with increasing proportions of seasonally available larger prey and consequently prey diversity. Brood size was negatively associated with the proportion of non-mammalian and predominantly forest-living prey.
Conclusions: The study highlighted the importance of comparative studies of raptor ecology across their geographical ranges in different environmental conditions to reveal undiscovered patterns, which may go undetected when conducting studies at the regional scale only.
This study aimed to evaluate the significance of dormice in the diets of predators in Europe and, as a result, expand the knowledge about dormouse ecology. A total of 535 sources containing information on dormice in the diets of predators were analysed. Countries of Southern and Central Europe stand out with the largest numbers of target sources. Dormice were recorded in the diets of 54 predator species: 23 mammals, 11 owls, 16 diurnal birds and 4 reptiles. Owls hunting in forests, particularly the tawny owl Strix aluco, are the main dormouse predators. The role of dormice in the diets of predators depends on dormouse abundance, and the highest proportion was recorded in the Mediterranean region, where edible dormice Glis glis are abundant. In particular periods, dormice may be an alternative prey for owls and some other predators. Dormice were seldom recorded in the winter diets of predators, especially in mammals, contrary to what was previously thought. Records of dormice in the winter diets of owls confirm that dormice leave their hibernacula during arousals in the thaw periods. The presence of dormice in the diets of diurnal birds suggests that nocturnal dormice may also be active in the daytime.
Both daily and seasonal year-round vocal activity of Ural owl were recorded in the Middle Volga River Region, Russia with the use of digital dictaphones. Two best-expressed peaks of longterm activity were revealed during the year: one starting in March and the other in September. In the spring, calls were recorded from 19:51 to 04:04. During this period, Ural owl’s total length of calls varied from 1 to 35 min per day, on average 12 min. The second annual peak was restricted to brood dispersal. In this period, the total duration of calls varied from 1 to 32 min per day, on average 9 min. In the spring, Ural owls always started calling from 24 min to 4 h after sunset. Vocalisation began at an average of 2 h 34 min after sunset. Completion of morning vocal activity always ended from 1 h 30 min to 2 h 40 min before sunrise.
