Distribution

Distribution of the Boreal Owl (Aegolius funereus)

The Boreal Owl (Aegolius funereus) [or Tengmalm's Owl] is a smaller owl species with predominantly nocturnal activity and a circumpolar Holarctic distribution. In Europe and North America, it mainly inhabits coniferous taiga forests (Mikkola 1983). The largest breeding populations of the Boreal Owl in Europe are found in Russia, Sweden, Finland, Belarus, and Norway. Relatively high abundance is also recorded in the Baltic states. Scattered, yet locally relatively abundant, breeding populations are also known from larger forest complexes in higher elevations of Central Europe, particularly from Austria, Germany, France, Switzerland, the Czech Republic, and Slovakia. Small local breeding populations also occur in the Netherlands, Spain, Italy, Bulgaria, and Greece. Isolated Southern European populations of the Boreal Owl are considered glacial relics whose current distribution is linked to climate changes following the end of the last ice age (Mikkola 1983, Korpimäki in Hagemeijer & Blair 1997).


Distribution of the Boreal Owl in the Czech Republic

Reports of Boreal Owl nesting date back to the 19th century, when the species was recorded as breeding in almost all border mountain ranges. However, specific nest discoveries remained relatively rare until the 1960s. Only since that period has the breeding of the Boreal Owl been confirmed across a greater number of sites in the Czech Republic (Hudec et al. 2005).

In South Bohemia, the Boreal Owl breeds at elevations ranging from 380 to 1,350 m a.s.l., though most nesting sites are situated between 700 and 1,000 m a.s.l. (Šťastný et al. 1997). Within the Czech Republic, its breeding has been confirmed mainly in the following mountain ranges: Bohemian Forest / Šumava (Kloubec 1990), Ore Mountains / Krušné hory (Drdáková 2002, Holý 2002), Jizera Mountains / Jizerské hory (Pokorný 2000), Giant Mountains / Krkonoše (Flousek 1985), Orlické Mountains / Orlické hory (Hromádko et al. 2005), Jeseníky Mountains (Suchý 2004, Poprach 2010), and the Beskids / Beskydy (Čapek 1994).

However, breeding has also been confirmed at lower elevations, for example in the Moravian Karst at 400–420 m a.s.l. (Mrlík 1994, Dvořák et al. 2002), in the Znojmo region (Tunka 1988), near Česká Třebová at 550 m a.s.l. (Tomeš 1997), in the Svitavy region (Urbánek 2001), Vyškov region (Bartl 2002), Třebíč region (Chobot J. & K. 2002), Jihlava region (Kunstmüller 2002), and Náchod region (Diviš 2004). These findings demonstrate that the breeding distribution of the Boreal Owl is not limited solely to mountain regions, but also includes suitable forest habitats in inland hilly areas (Hudec et al. 2005).

More recent atlas mapping of breeding bird distribution in the Czech Republic during 2014–2017 confirms the occurrence of the Boreal Owl primarily in mountain and submontane forest areas, as well as in certain forest complexes at lower elevations (Šťastný et al. 2021). In addition to most border mountain ranges, the species occurs, for example, in the sandstone regions of Bohemian Switzerland and Broumov, in South Bohemia, the Rokycany region, and the Bohemian-Moravian Highlands (NCA CR).

According to the latest evaluation by the NCA CR (Nature Conservation Agency of the Czech Republic), prepared as part of the reporting under Article 12 of the Birds Directive for the period 2019–2024, the breeding population of the Boreal Owl in the Czech Republic was estimated at 1,500–3,000 pairs (NCA CR 2025). Previous assessments from 2013 and 2019 reported 1,500–2,000 pairs. However, the widening of the population estimate range does not in itself demonstrate an actual increase in the species' abundance. When assessing population changes, it is also necessary to consider mapping intensity, availability of nest cavities, and interannual fluctuations in food supply.

König (1969) states that the spatial distribution of occupied nest cavities in suitable habitats is not uniform, but patchy (fragmented). This finding also corresponds with our own experiences from the Jeseníky Mountains.


Author: Karel Poprach