Boreal Owl Aegolius funereus


Justification of Red List Category
This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (extent of occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend appears to be fluctuating, and hence the species does not approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is extremely large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.

Population justification
The global population is estimated to number > c.1,700,000 individuals which equates to 1,130,000 mature individuals (Rich et al. 2004). The European population is estimated at 90,900-309,000 pairs, which equates to 182,000-619,000 mature individuals (BirdLife International 2015). Europe forms approximately 26% of the global range, so a very preliminary estimate of the global population size is 700,000-2,380,000 mature individuals, although further validation of this estimate is needed. The population is placed in the band 700,000-2,400,000 mature individuals.

Trend justification
The population is suspected to be fluctuating owing to fluctuations in prey populations. In Europe the population size is estimated to be fluctuating (BirdLife International 2015).


The breeding population of this species fluctuates with vole cycles and the depth of annual snow cover, which inhibits foraging. Forestry can reduce primary prey populations, remove forest structure necessary for foraging, and eliminate nest cavities (Holt et al. 1999). At one time the species frequently used old Black Woodpecker (Dryocopus martius) holes in Eurasia but declines in the species has resulted in less nesting opportunities (Mikkola 1983). Tawny owls (Strix aluco) and martens (Martes spp.) are serious predators of this species and in some years the latter can destroy a high percentage of broods and kill many females on the nest. In Germany, the Nuthatch (Sitta europea) may reduce the size of nest-hole entrances with plastered mud and has even been known to wall in brooding females, resulting in the birds starving to death. It is also vulnerable to pesticides (König et al. 2008)


Text account compilers
Ekstrom, J., Butchart, S. & Ashpole, J

Recommended citation
BirdLife International (2020) Species factsheet: Aegolius funereus. Downloaded from on 28/11/2020. Recommended citation for factsheets for more than one species: BirdLife International (2020) IUCN Red List for birds. Downloaded from on 28/11/2020.