Current Expansion of the Barn Owl (Tyto alba) (Tytonidae, Aves) in Northern Eurasia

In the northern part of Eurasia, until the mid-20th century, the barn owl (Tyto alba) was sporadically distributed only in the Baltic states, in the western parts of Belarus and Ukraine, and in Moldova. Once, in 1942, a vagrant bird was also caught in Turkmenistan. At the end of the 20th century, rare recordings of barn owls in Eastern Europe were reported, and, since the early 21st century, there has been pronounced expansion of these birds observed in the southern parts of Ukraine, Crimea, Ciscaucasia, and Transcaucasia. Different subspecies living in Central and Southern Europe and in the Middle East are simultaneously expanding their nesting areas, namely, T. a. guttata, T. a. alba, and T. a. erlangeri. However, visual identification of subspecies and clarification of the direction of their expansion are complicated by the similarity of various forms and their significant individual variability associated with the age, sex, intergradations with the neighboring subspecies, and other factors. The appearance of sedentary barn owls in new places is usually preceded by their post-nesting dispersion, which is variously directed and in some cases reaches 1000–2000 km from the place of birth. Owing to the expansion of its range, barn owl populations have increased many times in a number of regions in recent decades, but there are no accurate estimates of their numbers due to the rarity and sporadic nature of new findings, the highly secretive lifestyle of these birds, and insufficient knowledge of their ecology and ethology in the northern part of Eurasia. The taxonomy of various barn owl populations in Northern Eurasia and the major diagnostic characteristics of some subspecies living in the northern part of Eurasia are considered, and the features of their historical and current distribution and expansion in Eurasia are analyzed. The possible causes and mechanisms of the barn owl dispersion and the data on the dynamics of their numbers in different regions are considered.