LAUSR

* Correspondence: [email protected] The European continent represents a breeding area for 13 owl species (Mikkola, 1983). Their diet has been well documented for most species, especially in central and northern parts of the continent (e.g., Uttendörfer, 1952; Mikkola, 1983; Birrer, 2009). These diet studies were performed in various habitat types during different seasons and across dissimilar time spans. However, despite such a large number of studies, feeding habits of breeding owl species are still unknown for many vast regions (e.g., mountain ranges). One species that is relatively poorly investigated in such areas, particularly in southeastern and eastern Europe, is Tengmalm’s owl Aegolius funereus, a small forest-dwelling predator, which occurs in the taiga forest belt across Eurasia and North America (Mikkola, 1983; König and Weick, 2008). In the Balkan Peninsula, the Tengmalm’s owl population is regarded as a postglacial relict population (Simeonov et al., 1990). In Serbia, this rare nocturnal predator inhabits high mountain areas (>1000 m) covered with mixed and coniferous forests in the western and southwestern parts of the country (Rajković et al., 2010). Across the European continent, this owl species has been in the focus of numerous feeding ecology studies (e.g., Fredga, 1964; Sulkava and Sulkava, 1971; Jäderholm, 1987; Korpimäki, 1988; Kloubec and Vacík, 1990; Sorbi, 1995; Henrioux, 2010; Zárybnická et al., 2011). Nevertheless, all these studies were carried out in northern and central Europe, whereas data regarding southern relict, isolated, and patchy populations such as those from the Pyrenees or Balkan Peninsula are scarce or completely lacking. So far, for the Balkan Peninsula, there is only one published article about the diet of Tengmalm’s owl. This research, based on an investigation of only one family, was carried out on Mt. Rila in western Bulgaria (Simeonov, 1980). Data from other Balkan countries have not been published yet. The main aim of this study was to describe and analyze the diet composition and prey diversity of Tengmalm’s owl from the southeastern border of its distribution range in Europe recorded during the breeding period of 3 consecutive years. Field work was conducted in part of Kopaonik National Park (hereinafter Mt. Kopaonik) in central Serbia (43.28°N, 20.80°E; altitudinal range 800–2017 m). The study area covered approximately 25 km2 and is situated in the central part of the national park. About 75% of the study area consists of high-mountain forests (mostly Norway spruce, Picea abies), 22% of open grassland-rocky terrain, and 3% of built-up areas. A detailed description of the study area can be found in earlier publications (Rajković et al., 2010, 2013). Abstract: Annual variation in the diet, composition, and prey diversity of Tengmalm’s owl Aegolius funereus (Linnaeus, 1758) was investigated in high-mountain coniferous forests of Mt. Kopaonik (central Serbia) during 3 consecutive years. Prey remains and decomposed pellets (detritus) were collected at the bottom of nest-boxes during 2 separate periods: during mating and after nesting. Prey remains such as maxillae, mandibles, beaks, or feathers were used for prey identification. In total, 438 prey items were separated and identified. Small mammals represented the most numerous class of prey (87.23%). The most frequent prey item was bank vole Myodes glareolus (23.29%). During the nesting season the proportion of voles eaten was significantly higher in comparison with the mating period. The mean prey weight was 20.74 g. In the study area, according to diversity index calculations, prey diversity was high and it seems that the number of breeding attempts by Tengmalm’s owl showed dependence on the annual abundance of small rodents, but further research is needed to confirm this assertion.