Spatial and temporal diversity of the diet of the tawny owl (Strix aluco)
Authors: Obuch Ján 
Published: August 2012

Spatial and temporal diversity of the diet of the tawny owl (Strix aluco)

The author compared diet of eight owl species in Slovakia, out of which four species prey in the non-forest environment (Bubo bubo, Tyto alba, Asio otus and Athene noctua), while the other four species prey mostly in the forest (Glaucidium passerinum, Aegolius funereus, Strix uralensis and Strix aluco). Tawny owl (Strix aluco) has shown the highest degree of adaptability when it comes to various types of environment and broad diversity of prey. Appendix 1 presents material of total 225,441 pieces of diet, which contains 69 species of mammals and at least 147 species of birds. While B. bubo diet is typical especially for high presence of bigger prey species within mammals and birds (66 diagnostic taxa), diet of S. aluco is characterized by as many as 89 taxa with higher share than the average of all eight compared owls (taxa with values 1+ and 2+ in blocks as marked by full line). Based on the analysis of 68,070 pieces of S. aluco diet collected in Slovakia, it is possible to differentiate seven basic diet types: A - from lower mountains, B - from middle montane locations, C - from colder and more humid parts of mountains, D - characterized by high share of bats (Chiroptera), E - characterized by high share of slugs (Limacidae), F - from floodplain forests, and finally G - from environment strongly influenced by humans. Diagnostic species for one or several diet types are characterized by markedly higher share than Slovak average. By the large amount of analyzed samples of S. aluco diet it is possible to gain the knowledge about structure of several animal groups from relatively little disrupted forest ecosystems and those from environment to some degree influenced by humans. Diet types represent simplified models, which are understood in a different sense than plant communities. Individual disposition for specific food preference (e. g. Chiroptera) also plays an important role by some tawny owl's specimens. Some types of prey can be further divided into undertypes (e. g. undertypes G1 and G2 in Table 1). Diet of S. aluco has been examined more in detail and over a longer period of time especially in following national parks: Slovenský kras, Muránska planina and Veľká Fatra Mts. Samples from other parts of Slovakia are also presented here according to their relevance to particular diet types. Pellets of S. aluco were collected over a longer period of time (up to 30 years) in several sites and it is chronological periodicity in presentence of diagnostic species, which stands in focus. Long-term changes in S. aluco diet during Holocene were examined in two parts of Veľká Fatra Mts, which are influenced by climatic changes as well as human activity (deforestation and pasture). The author has occasionally collected pellets of S. aluco in several mountains of Europe between Western Alps and Caucasus and from northern border in S. aluco areal, from Trondheim area in Norway. Furthermore, the author presents hereby his own material from pellets of S. aluco from the Middle East to Himalaya (in particular countries of Jordan, Israel, Lebanon, Syria, Turkey, Iran, Kyrgyzstan and Nepal).