Barbary sheep is a nonnative animal species in Croatia that lives on the Mosor Mountain. In 2002, five Barbary sheep individuals escaped from captivity, resulting in today's population, which is estimated at around 140 individuals. While in the native habitat the population is endangered due to poaching and habitat loss , and the species is listed on the IUCN Red List, most of the introduced populations have shown high adaptability to new habitats and a high potential for spreading to new habitats. Since ungulates play a key role in ecosystems, knowledge of their morphological, biological and ecological characteristics is necessary for their proper management. Non-native ungulates can pose a serious threat to native biodiversity. Some non-native species of ungulates are known to have a negative impact on the areas into which they have been introduced. These include predation, competition with native wildlife, diseases and their associated consequences, hybridization and habitat alteration. Due to the high growth rate and the ability to adapt to the diet, the results from the areas where the Barbary sheep was introduced (Spain and the USA) show a rapid process of dispersion and population increase, which is not the case on Mosor Mountain. The motive of the research was to obtain the first information about the non-native ungulate species that has been present on Mosor Mountain in open nature for twenty years using modern and appropriate methods. Although so far there is no empirical evidence related to any negative impact on native fauna or flora from Barbary sheep, due to general and scientifically unconfirmed theses, there is a negative opinion about this species in society. Insights into autochthonous and nonnative populations of Barbary sheep with an emphasis on their ecological, biological and morphological characteristics present the current knowledge about the species. The chronology of the arrival of the Barbary sheep in Croatia is shown, and the habitat where they were introduced, Mosor Mountain, is discussed through the relief and climatic features of the plant community. To determine the daily activity, habitat choice and dispersion estimation using two different methods, we caught and marked one of the animals with GPS-GSM collars. No mortality was recorded while capturing and tagging animals with collars. The total monitoring of marked animals lasted from 2015. to 2019. Daily activity in the research was measured using an accelerometer built into GPS-GSM collars and a separate measurement of the collar's movement speed in 2 rectangular directions. The information obtained from the two-axis sensor is not a binary activity status (active-passive), but a numerical value, the result of the intensity and duration of the collar's movement. The accelerometer measures activity using the x-axis and the y-axis. From the x-axis and y-axis values, we obtained the total activity (VA) in the formula VA=sqrt(x2 +y2). The collars we placed on the animals were programmed to record the location of the tracked animal (GPS coordinates) every two hours. All the data from the GPS-GSM collars was presented within the ArcGIS PRO program and further enriched using GIS analyzes and publicly available data. We analyzed daily movements, habitat area, habitat characteristics and changes in space use during the warm and cold part of the year. For the purposes of determining dietary habits, samples of rumen content were taken from animals that were legally shot on Mosor Mountain. Analyzes of rumen content samples of Barbary sheep were made according to the methodology of Klansek et al. (1995). The morphological characteristics of the body and horn growth were determined on 30 samples of Barbary sheep (20 M, 10 F) that were legally caught from 2014. to 2019. on Mosor Mountain. The measurements were taken just after the individual was shot in the mountain. All measurements were made by the same person using standard methodology. We analyzed females and males separately, due to pronounced sexual dimorphism. The results of daily activity showed a typical bimodal pattern of activity with two peaks, the first in the morning between 5:00 and 9:00 a.m., and the second in the afternoon between 4:00 and 7:00 p.m. Afternoon activity is more pronounced than morning activity and lasts longer. The peak of activity changed in accordance with the seasonal dynamics of the photoperiod. period of the lowest activity is in winter before dawn. The home range of Barbary sheep on Mosor Mountain is the mountain ridge and southeastern exposure. The monitored animals moved an average of 1.46 km per day, and the area of their annual home range is on average 1872 ha. Data suggest that the dispersal of Barbary sheep is limited to the Mosor Mountain area and is unlikely to spread. The activity was mostly circular and vertical in home range and during the research, not a single tracked animal moved away from the Mosor Mountain, and they very rarely stay on the northern slopes. Barbary sheep prefer and use extremely steep, rough and sunny terrains of the Mosor Mountain with altitudes above 650 m/s. They spend most of their time on rocks and in deciduous forests. They show the greatest tendency to use rock creep, where there are very few in the habitat, while they use the forest habitat types a lot, but do not prefer them. During the cold part of the year, Barbary sheep use terrains with a lower altitude and sunnier exposures with a greater slope. The species is of the pasture type, very flexible in terms of diet and shows large seasonal variations. The main part of the diet consisted of various grasses and leaves of deciduous trees. During the summer, they consumed much more leaves of deciduous trees than in other seasons, which may indicate that they use it as a substitute for water. The results of the quantitative morphological characteristics of Barbary sheep from Mosor Mountain suggest that this population is well adapted to the Mediterranean habitat and indicate that they do not differ significantly from other populations either in autochthonous or non-native habitats. Males had significantly higher mean values of all quantitative variables, which explains the pronounced sexual dimorphism of this species. The results of this research indicate new knowledge about the life habits of this species in the free nature of the Mediterranean habitat, and will contribute to better management of nonnative species in Croatia, which will preserve biological diversity and the ecosystem in its original form.