The mound-building mouse (Mus spicilegus) in Western Podillia: expansion on the left bank of the Dnister

New findings of the mound-building mouse on the left bank of the Dniester in the interfluve of its tributaries—the Dzhuryn and the Nichlava (Chortkiv Raion, Ternopil Oblast)—are described. The presence of Mus spicilegus was established based on findings of food stocks common for this species in the form of mounds, which are easy to detect in the field and which can be clearly diagnosed. Both single mounds and their clusters were taken into account. The specifics of biotopic distribution, formation of food reserves, and the role in trophic chains of this species under conditions of the studied region are indicated. The mound-building mouse is one of the few rodent species that maintain a high abundance under conditions of intensive agriculture, which involves mechanical tillage several times a year and a significant level of chemical use. The distribution of the studied species is influenced primarily by two factors: the level of agricultural techniques in agricultural production (arable farming and crop care, quality of harvesting) and the distance from uncultivated areas. The mound-building mouse usually inhabits agricultural lands with a low level of agriculture (minimal chemicalization and mechanical tillage). These are lands allocated for private gardening or farming. Such lands have increased weeds and crop losses during harvesting, which creates a rich food base. After harvesting, such lands usually do not undergo long-term tillage. Results show that the settlement of arable lands comes from natural or other uncultivated areas, where the nuclei of populations are concentrated. In autumn, under the above favourable conditions, population growth is observed in adjacent cultivated lands, where winter food reserves are formed in the form of characteristic mounds. On large-area crops of monocultures cultivated by large agricultural firms, mounds are usually absent. The level of agro-technical pressure on the same area varies from year to year. This causes temporary instability in the appearance of mounds. They disappear where anthropogenic impact has re-emerged significantly and re-appear where there has been a weakening. The role of the mound-building mouse in trophic chains and in maintaining regional biodiversity is shown