Red deer (Cervus elaphus) exhibit specific behaviour during the rutting season, which may have an impact on the safety on cervid farms, both due to aggressive interactions between animals and the safety of people staying there, such as staff and tourists. This issue applies especially to stags whose behaviour changes radically, and the correct interpretation of the observed changes is very important. Therefore, the aim of the study was to analyse the pre-rut behaviour of stags and to show the influence of atmospheric conditions on vocalization and other elements of their behaviour, which facilitate determination of the onset of the rutting season. The observations were conducted in August and September of 2017 and 2018. It was shown that lower temperatures, declines in air humidity, increasing atmospheric pressure, and transition of the moon phase towards the full moon resulted in intensification of the vocalization activity in the red deer in the pre-rutting season, which may accelerate the rutting period in the deer males. The number of vocalizations varied between the years and depended on the mean temperature, air humidity, atmospheric pressure, and moon phase in the pre-rutting and rutting seasons. Through observation of the changing weather conditions, it is possible to predict the time of increased activity of stags and the onset of the rutting period. Predicting the date of mating season in farm breeding, based on daily observations of changes in the behaviour of stags, can be helpful in planning veterinary treatments or selecting the composition of the hinds to be covered by specific stags, which can also contribute to the improvement of their welfare.