To know and to protect.

The research of functional and numerical response of Boreal owl to long-term environmental changes in air-polluted areas of Central Europe as a background for better protection of this species

One of the main tasks of Nature conservation is a conservation of biodiversity. That is why the species whose populations are threatened with extinction in local or even global scale are protected. Effective plant and animal protection, including protection of habitats, is the prerequisite for assuring biodiversity protection at the species level. The European union and its states regulate the protection of threatened species by law and invest finance in measures that eliminate or reduce known threatening factors and improve the conditions for life of such species. For optimalization of these investments it is necessary to plan the measures with the perfect knowledges of biology and ecology of protected species, the knowledges of local population´s and its environmental conditions and main limiting factors.

Boreal owl is a species protected by the European directives (№2009/147/EC, Annex I) and Czech law (№114/1992 Coll.) as well. It is a subject of protection in several Special Protection Areas (SPAs) in Central Europe, where the forest ecosystem was damaged because of air-pollutions in the eighties of the 20th century. Then the areas were afforested, and the growing of young forest cover projected into changes of animal associations. Also, the population of Boreal owl reflects this process and the most limiting factor for population has changed as well.

The distribution of this cavity-nesting species can be limited by the availability of suitable habitats, availability of nesting sites, food availability, interspecific and intraspecific competition and climatic conditions.

Fig. 1.: The Boreal Owl (Aegolius funereus)

We have studied the Boreal Owl population in The Jizera Mountains Protected Landscape Area since early nineties of 20th century. There is a central mountain plateaus (about 700–800 m.a.s.), where the forest ecosystems were nearly completely damaged because of air-pollutions in the eighties. There were no natural availability of nesting, so this was the main limiting factor for Boreal Owl.

Fig. 2.: The Jizera mountains in early nineties of 20th century

There were also big problems with reforestation of the open areas and forest clearings (dominated by wood reed Calamagrostis villosa) with only solitary trees. High densities of Microtus voles (as pests of young trees) and bad habitat quality for their avian predators were factors which made the situation worse. The system of more than 600 nest boxes for Boreal Owl were installed there to enhance a habitat quality for the protected species and for a purpose of supporting the natural defence ability and stability of forest ecosystem.

Fig. 3: Nest box for Boreal Owl

The proportion of occupied nest boxes continuously grave up first (in nineties) and then it started to fluctuate synchronously with the abundancy of small mammals as a main prey of Boreal Owl. The nest possibilities (presence of nest cavities) and food conditions (the density and the availability of prey) seemed to be the most important factors affecting the abundancy of Boreal Owl breeding population. As soon as the nest possibilities were sufficient, the prey abundancy and availability became the most important factor.

The system of nest boxes has been maintained, so the availability of nest cavity is stable but the main habitat has changed from open areas with solitary trees in nineties of 20th century to young spruce thicket at the present time.

Figure 4: Currently the central plateau of Jizera Mountains is covered mainly by growth of young trees (mainly Norway spruce and Blue spruce)

In northern Europe, the centre of the Boreal Owls’ range, the species frequently inhabits Norway Spruce Picea abies forests. More or less isolated populations occur in central and southern Europe where this owl inhabits coniferous, mixed or deciduous forests mainly in mountain areas. In central Europe, population densities of this owl are usually stable, for example, in Slovakia (Danko et al. 2002) and Poland (Sikora et al. 2007), or even increasing, for example, in the Czech Republic (Šťastný et al. 2006). However, the population densities of northern European Boreal Owl populations, especially in Finland and Sweden, are declining due to the decreasing area of old coniferous forests (Laaksonen et al. 2004, Korpimäki & Hakkarainen 2012).

In contrary with the trend of whole population in the Czech Republic, the abundance of Boreal Owl in the Jizera mountains (after population growth in nineties) has decreased during last 20 years. The big changes of environment occurred there in the context of reforesting and growing young forest. But there were no decreasing areas of old forests in this period as it happened in Scandinavia. So, what’s the reason of population decline in the Jizera mountains? The main change is decreasing of proportion of open areas and clearings and increasing proportion of young forest there. One of the aims of my study is to test the effect of proportion of open areas and clearings and proportion of forest in different age categories on nest box occupancy (and partly also on diet composition) of the central European Boreal Owl. We want to find out if the age of forest is an important factor and if high dominancy of young dense forests with minimum open areas or old forests in environment could be a limiting factor for Boreal owl.

Fig.5: We will make GIS analysis with using Forestry maps of growth to find out how is the occupancy of nest boxes influenced by habitat cover in its surrounding and how does it change with successive changes.

And what else has changed with succession of habitat? We also want to find out how the food availability has changed during these successive changes of environment, how the structure and the dynamics of small mammals synusia have changed and how it reflects in owl’s preferences of prey.

Fig. 6: The pellets and rests of prey from nest boxes are collected after the breeding season, the osteological material is separated, and prey items are identified into a species.

The thesis aim is to evaluate the numerical and functional answer of Boreal owl to long-term changes of its environment from the nineties of the 20th century to present and bring new knowledge for better protection of this species not only in The Jizera Mountains Protected Landscape Area but also in other areas in Central Europe where the forest ecosystem breakdown and big successive changes happened (or will happen in future).