Notes on the reproduction, breeding biology and ethology of the Eurasian pygmy owl (Glaucidium passerinum) in Slovakia
Authors: Pačenovský Samuel , Šotnár Karol 
Published: May 2012

Notes on the reproduction, breeding biology and ethology of the Eurasian pygmy owl (Glaucidium passerinum) in Slovakia
Accessible data on 78 breeding occurrences of the Eurasian pygmy owl (Glaucidium passerinum) in Slovakia are evaluated. Data from the oldest known breeding in 1846 up to 2010 were used. The breeding of this species has been proved in 24 orographic units, at altitudes from 450 (400) to 1450 m. Distribution of the species in Slovakia closely follows the distribution of fir (Abies alba) and spruce (Picea abies) and breeding has also been recorded in forest habitats with an abundance of scots pine (Pinus silvestris) and black pine (Pinus nigra). From the point of view of natural and secondary origin of these forest habitats, the species breeds in both ‘natural’ habitats such as montane spruce forests and Euro-Siberian coniferous forests, forests with beech and fir, oak-hornbeam forests with lime and fir, as well as in secondary forest spruce plantations. From 22 evaluated Slovakian nests as many as 17 (70.8%) were situated no farther than 200 m from water. A high number of nests (72.5%) were situated at altitudes between 600-1100 m, with 13% above this range and 14.5% below. As many as 25 nest holes were located in spruce, both living and dead, and in snags, ten in fir (with a significant number of dead stumps), six in beech, four in oak and four in aspen. Nests were also found on one occasion each in larch, maple and black pine. On one occasion breeding took place in a nest-box. On several occasions the same nest hole was used repeatedly, with the highest number of such occasions being four times in the same tree in an eight year period. On three occasions a shift of nest location of ca. 200-350 m within the same territory occurred and two neighbouring pairs, and nests, were once found at the same time just 400 m from each other. Nest holes excavated by the Dendrocopos major and Picoides tridactylus are often used. On four occasions breeding took place in natural cavities (2x beech, 1x larch, 1x maple). The lowest situated nest was placed lower than one m above ground level and the highest 13 m above the ground. From 44 evaluated nest holes the highest number (26) were situated between 4-7 m. The production of young was evaluated in 57 cases, 34 of which were successful (69.7%). Young were found on 27 occasions, from which 80 fledged: an average of 2.96 per nest. This average is slightly lower than that calculated in Austria and Germany. In the colder than usual years of 2009 and 2010, which were poorer in food availability and characterized by high precipitation, the numbers of fledglings was even lower: on average only 2.3 and 2.0 fledglings per nest respectively. The average number of fledglings per nest from 8 Slovakian nests in three consecutive years (1989 to 1991) was 3.75 fledglings per nest but the same parameter from nine Slovakian nests in six years (2005 to 2010) dropped to 2.88. This indicates a diminishing trend in nest productivity. On one occasion the movements of fledglings in the territory after their fledging were observed for 27 days. On other occasions disturbance due to human activity (tree felling) was recorded as the reason for an abandoned breeding attempt. Such disturbance can be extreme, for example, in the Kysuce Region in the Javorníky Mts and Turzovská vrchovina Mts, two breeding sites with nests in 1999 and 2003 were later destroyed because of complete removal of those forest tracts attacked by bark-beetles. In 2009 in the Strážovské vrchy Mts, a curious case was observed where, during the period of parent care of nestlings, the male disappeared but the female continued to feed her two nestlings alone until they fledged. Just after fledging these fledglings were predated, probably by a Pernis apivorus or an Accipiter nisus, both of which bred nearby. The authors made several remarkable ethological observations in the life of Eurasian pygmy owls. In the Strážovské vrchy Mts the ‘nest-showing’ of more than one cavity in its territory by the male to the female was observed. Copulation was observed a total of eleven times during the months February - May in the years 1989-2010, with the following frequency: February 1x, March 3x, first half of April 5x, second half of April 1x, beginning of May 1x. Interactions of the Eurasian pygmy owls with diurnal raptors, other owl species and other cavity-breeders were also documented. In the Strážovské vrchy Mts the breeding of an Eurasian pygmy owl pair at a relatively close distance to the nests of various diurnal raptors were as follows (species/distance from nest of the raptor from nest of the Eurasian pygmy owl): Pernis apivorus 7 m, Accipiter nisus 230 m, Buteo buteo 250 m, Aquila pomarina 500 m, Accipiter gentilis 700 m. In the Volovské vrchy Mts a pair of Eurasian pygmy owls successfully bred at a distance of 600 m from two nests of Strix uralensis, and another pair bred at a distance of 500 m from a nest of Strix aluco. The breeding of another pair of Strix aluco just 30 m from a cavity used by a pair of Eurasian pygmy owl led to unsuccessful breeding/abandoned nest by this pair. Competitive behaviour was observed between the Eurasian pygmy owl and other cavity-breeders such as Sitta europaea and Dendrocopos major, and an occasion of the predatory killing of an owl fledgling by Strix uralensis was suspected. An attack by Aegolius funereus on a Eurasian pygmy owl was also observed.