**5. Conclusions**

Only the Pygmy Owl declined after a near 30 year period (steep decline by −2 from 8 to 5 territories); its local decline is referred to increased presence of Tawny Owl at the site. Only 23% of site visits were effective to locate calls of the species in

#### *Qualitative and Quantitative Changes in a Guild of Forest Owls: Eurasian Pygmy Owl… DOI: http://dx.doi.org/10.5772/intechopen.102932*

years 2020–2021 in comparison to 90.8% of positive site visits in 1989 and 83% of positive visits in years 1989–1994. This fact was probably caused by decline of calling activity of Pygmy Owl in sympatric areas with Tawny Owls. Two other species showed steep population increase +2: the Tawny Owl almost doubled its population at the site, from 3 territories (mostly females only) in 1989–1994 to 5 territories occupied in 2017–2021 and the Boreal Owl was almost absent during 1989–1994 and appeared as regularly occurring territorial species with 8 occupied breeding territories in years 2017–2021. In case of Tawny Owl, there is a tendency of spreading to higher elevations and in the case of Boreal Owl an opposite tendency, looking for suitable breeding habitats in old fir-beech forests with fir and oak stands and Black Woodpecker holes in old beeches as low as below 500 m a.s.l., presumably due to profound habitat loss going on recently in higher, central and W parts of the same mountain range, in elevations about 1000 m a.s.l., where optimal conditions for the species were worsened after year 2000 due to large-scale drying up and destruction of spruce forests. One species, the Ural Owl remained stable at the site between years 1989–2021 with a continual total population of about 8 pairs. Wider regional comparison of the site at the scale of whole Volovské mountains range was given in chapter 3.

Earlier published studies of diet of Pygmy Owl [20] in years 2012–2015, including data from 3 nests located in higher elevations of Volovské mountains revealed an existing wide food supply for the species, including at least 6 mammal and 22 bird species found in diet of these 3 Pygmy Owl pairs. These data support an assumption, that local decline of the Pygmy Owl at observed study site Bankov-Kamenný hrb was not caused by food shortage. On the other hand, good populations of small mammals in the forest and open habitats (meadows, clear-cuts), able to maintain good and stable populations of Ural Owls could possibly attract some Boreal Owls to as low areas as that site, to lowest known elevation limit of the species in Slovakia. It has been concluded that some of quite recent, new, already published data on occurrence of Pygmy Owl in its lower distribution limit, e.g., as those on first documented breeding of the species in Aggtelek karst in N Hungary from 2011 [21] could be explained by a partial population decline and large-scale habitat loss going on in some areas of Volovské mountains, located only 13 km to N from edge of the Aggtelek karst area in Hungary. Still, the study area of 5.2 km2 is quite small, so wider conclusions on population trends of these 4 owl species should be taken carefully and further research is needed, on a larger scale.
