Abstract: The Eurasian Nuthatch is a common bird species that uses artificial nest boxes for roosting in many areas across Europe. However, the knowledge about its roosting habits in urban habitats is lacking. In our study, conducted across three study sites in the city of Bratislava (forest, and two parklands), we observed this species roosting 151 times (1.7% of 9153 checked boxes). The mean nest-box occupancy by roosting Nuthatches, as well as their proportion among roosting birds, decreased from oakwood to parklands, varied significantly between checks, seasons, and was positively correlated with the number of roosting Great Tits. Mean relative air humidity and precipitation between 18:00 and 19:00 positively influenced nest box occupancy. The number of roosting Nuthatches also varied within a single winter (October to February), with the highest numbers recorded in November and December. A significant prevalence of recorded males was observed only in two parklands (accounting for 83.3% N = 18 and 79.2%, N = 22 of all records, respectively), while in woodland habitat, the sex ratio was nearly equal (males comprised 51.1%, N=94). Within a single winter season, 36.2% of roosting birds (N =58) were faithful to their roosting locality (i.e., recorded more than once in the season), with a mean fidelity rate of 0.1. Individuals recaptured over multiple winter seasons were observed only in the woodland area, accounting for 17.1% (N =35).

Key words: overnighting, urban ecology, cavity nesting birds, Slovakia