Territories and home-ranges are the smallest spatial units of species' presence in a landscape and they determine in what ways and on what scales animals perceive and use their environments. Their sufficient sizes encompassing enough resources are critical for survival and reproduction of individuals. Processes and factors affecting territory and home-range sizes therefore belong to fundamental ecological issues. Despite its importance, the knowledge of variation in avian territory and home-range size at large spatial scales is poor. So far it has comprised mainly the findings that the used area is determined by individual's energetic demands, dependent on body size and diet type, and by environmental productivity. Therefore, the aim of this thesis was to use data gathered from available literature to describe the variation in territory and home-range size of birds. I was curious what was the nature of territory and home-range size frequency distribution; whether the sizes were species-specific and whether and how these sizes were affected (beside the body mass and diet type) by various environmental characteristics, such as latitude, temperature, precipitation, seasonality, altitude and habitat type. I have found that the territory and home-range size frequency distribution is approximately...