Tree-dwelling bats are an important component of the forest ecosystem, however they are dependent on a sufficient number of available roosts, as they frequently switch roosts due to the fission-fusion dynamics of bat colonies. Roost switching is closely related to the dawn swarming, serving as a source of information for the choice of the new roost. The main aim of our thesis was to expand the knowledge about this unique social behaviour and the mechanisms behind it, whereas previous findings were mostly anecdotal and lacked further details. Most of the results are based on a maternity colony of Daubenton’s bat (Myotis daubentonii) but data on Leisler’s bats (Nyctalus leisleri) were employed too. Using a combination of different methodological approaches such as passive integrative transponders (PIT-tags) and automatic RFID readers, microsatellite genotyping of individuals, an enzyme immunoassay from bat droppings and an agent-based computational model, we found that: 1) The pattern of dawn swarming differs between sexes and age categories. Juveniles and yearlings mainly swarm around dawn, with no particular pattern, while old females swarm as the main part of the colony during most of the night, with a gradual increase from midnight onwards. This difference may be related to the learning status of the young bats. Old males swarm at least because of their solitary lives. 2) Old females increase their swarming activity during the time when juveniles are capable of flying, in order to guide them within the colony area or to teach them swarming behaviour itself. In addition, old females and juveniles swarm together more often than dyads of adult females only. Kinship is an important factor in the formation of swarming dyads only in youth, towards adulthood the effect of kinship diminishes. 3) Swarming behaviour may be correlated with an elevated cortisol levels as a result of roost switching due to stressor exposure, as is predation or unsuitable microclimatic conditions. 4) Swarming activity may serve as an indicator of individual’ colony affiliation. Male yearlings tend to stay with their natal colony after their first hibernation due to mating options or toleration by the adults. This is reflected in their increased swarming activity during spring. 5) The agent-based model Skybat, based on an algorithm of swarming behaviour was successfully used to predict the effects of roosts shortage on population size. When social bonds between colony members were assumed to be strong, a 50% decrease in the number of available roosts led to area abandonment. In summary, research into this behavioural phenomenon found a practical application in biological conservation yet, with the potential for further research from the perspective of many biological or non-biological disciplines.