Brown bear movement patterns are driven by their opportunistic feeding behaviour, with their complex life history and seasonality playing an important role in habitat selection. Within a large unfragmented forest habitats persisting over decades in the Romanian Carpathians and a prohibitive hunting management during 40 years of communist centralised game management, information about brown bear movements and spatial ecology is lacking. Using data obtained from 13 brown bears fitted with GPS telemetry collars, we estimated home ranges and core activity areas and we investigated the daily, seasonal and altitudinal movements of brown bears in the Eastern Romanian Carpathians and surrounding high hills. The median MCP95% home ranges of brown bears was 629.92 km² and the median size of core activity areas (estimated as 50% kernel density) was 36.37 km², with no significant differences between males and females. The mean daily distance travelled, measured as daily displacement length, was 1818 m and an analysis of seasonal movements indicated significant differences between seasons (greatest movements during the Hyperphagia season). The GPS-collared brown bears travelled between a minimum altitude measured at ~234 m and a maximum at ~1634 m. Analysing the spatial overlap between the estimated home range and the game management units (GMU) limits, we obtained a median number of 8 GMUs overlapping totally or partially with estimated home range polygons. Our study, using GPS telemetry, highlights the complex spatial ecology of the brown bear in the Romanian Carpathians, with larger home range size than those estimated in other European brown bear populations and with daily movements that vary by season and within a large altitude range. Our study supports the implementation of brown bear monitoring at a regional scale, rather than focusing on county level GMUs as the monitoring unit.

Daily movements, home range, Romanian Carpathians, Ursus arctos

Understanding animal movement patterns is crucial for wildlife management and conservation (Kernohan et al. 2001). Movements of individuals in their forays for food, switching between habitats, defending cubs or food resources, are of high interest for understanding the ecology of brown bears in heterogeneous landscapes (Martin et al. 2013). The use of telemetry to obtain movement data has been adopted in brown bear research studies for decades, e.g., movement patterns in Kodiak Island or denning ecology in Yellowstone (Berns and Hensel 1972, Craighead and Craighead 1972). Telemetry was also used to provide information about brown bear habitat suitability in the Alps (Guthlin et al. 2011) or predicting human-bear conflicts in the Dinaric Mountains (Jerina et al. 2012). Analysis of animal movement data leads to a deeper understanding of key environmental resources required for population persistence (Margules and Pressey 2010), which aids resource managers in developing wildlife management strategies. Worldwide, brown bear population management (e.g., for North American, Dinaric, Scandinavian, Alpine brown bear populations) has been heavily influenced by the results of telemetry studies over the past four decades. In Croatia, telemetry studies have been critical for quantifying home range sizes, the overlap between individual home ranges, as well as the gender differences in home range sizes (Huber and Roth 1993). These data have been used in developing the brown bear management plan for the Republic of Croatia.

Brown bear movement patterns and spatial ecology are driven by their complex life history and seasonality plays an important role in their selection of habitats (Pop et al. 2018). Brown bears are opportunistic omnivores (Bojarska and Selva 2012, Kavcic et al. 2015) and their movements are heavily influenced by food resource availability (Nielsen et al. 2006, Stofik et al. 2013, Ciucci et al. 2014, Kavcic et al. 2015). In addition to food availability, other factors such as reproductive stage, den site availability or avoidance of conspecifics or predators, can affect the movement of individuals, which further poses challenges to understanding space use patterns (Nathan et al. 2008). Furthermore, environmental characteristics such as the reproduction period, air temperature or daylight length are also important in understanding the seasonality of brown bear movements (Nielsen et al. 2006, Martin 2009, Ware et al. 2013).

Large unfragmented forest habitats, persisting over decades in the Romanian Carpathians and surrounding high hills (Rozylowicz et al. 2011, Patru-Stupariu et al. 2013), and a prohibitive hunting management during 40 years of communist centralised game administration, had contributed to the maintenance of the largest and most stable European brown bear population (Chapron et al. 2014, Popescu et al. 2016). Romania’s brown bear population inhabits the Carpathian mountains and surrounding high hills, which are characterised by low human density, but with intensive use of natural resources (e.g., timber and non-timber forest products) and livestock grazing. The highest brown bear densities, of up to 11 individuals/100 km² occur in Eastern Carpathians (Cazacu et al. 2014, Popescu et al. 2017). However, no studies to date have documented the movement ecology of Romanian brown bears at individual and population levels, leading to suboptimal management strategies (Popescu et al. 2016).

In Romania, brown bear ecology data are collected via opportunistic observations at feeding stations or using methodologies for counting track signs (Popescu et al. 2016) which lack statistical rigor and ignore the complex bear space use patterns (Lindstedt et al. 1986, Dahle and Swenson 2003). These monitoring deficiencies lead to a poor understanding of brown bear movements and habitat selection. Published data on space requirements or home range sizes of Romanian brown bears have been based on expert opinion and varied from 15–20 km² for an individual (Comsia 1961) to 200 km² for males and 50 km² for females (Maanen et al. 2002). Management decisions, made at the level of game management unit (GMU), may be suboptimal, given that GMUs are on average ~120 km² in size, thus potentially failing to capture the full extent of movement and space use of a single individual.

The aim of the study is to investigate brown bear movement ecology and space use in the Eastern Carpathians and surrounding high hills (Subcarpathians), Romania. We take advantage of a large dataset of Romanian brown bear GPS telemetry gathered between 2011 and 2015 within the framework of several large carnivore conservation projects to quantify annual and seasonal home ranges. We specifically evaluate whether differences in home range sizes exist between males and females, as well as between adults and sub-adults (Dahle and Swenson 2003). To test the validity of using GMUs for brown bear management, we analyse the overlap between individual home ranges, core activity centers and the game management units. Lastly, we investigate the daily, seasonal and altitudinal movements of brown bears across four different seasons with varying food availability (Ciucci et al. 2014, Roellig et al. 2014).

Our analysis of brown bear movement and space use from GPS telemetry data showed that previous predictions on bear movement ecology and home range sizes from the Romanian Carpathians (e.g., Comsia 1961, Maanen et al. 2002) were not realistic. The estimated median MCP95% home range (~630 km²) and median home range core areas (~36 km²) were more than three times larger than published information. Furthermore, our estimated home range size was higher than brown bear home ranges in the Northern or Southern Europe (Dahle and Swenson 2003, Dahle et al. 2006, Gavrilov et al. 2015). Individual seasonal home ranges varied from a few square kilometres to over 2000 km² (see Table 3) and, for the Hyperphagia season, home ranges had larger values (see Figure 3), although we did not detect significant differences between seasons. Our results also show that there are no differences between age groups or between males and females, which contradicts findings from other European studies (Dahle and Swenson 2003). However, we did detect higher variation in home range size for males and subadults.

The number of core areas identified for each bear varied between 1 to 4, while the median area of activity centres (KDE50) was estimated at under 40 km², demonstrating that bears may intensively use several areas during a year and such areas can be larger than a GMU. The median number of 8 GMUs overlapping with individual home ranges (MCP95% home ranges) and 3 GMUs overlapping with home range core areas (KDE50 core areas), suggest that the size of GMUs in our study area (mean = 126.97 km²) might not be suitable for planning bear management and especially as a population census base unit, as done presently. Thus, GMUs as sampling units might be a biased approach that can lead to poor management decisions at the population level, such as overharvesting (Popescu et al. 2016) or unnecessary supplementary feeding (Selva et al. 2017). Planning further census techniques should consider that male home ranges overlap more GMUs than those of the females (see Figures 4 and 5), mostly as a result of the brown bear mating system (Dahle and Swenson 2003).

This study presents the first extensive assessment of space use and movements for brown bears in the Romanian Carpathians. Our results show larger home range size in Romania compared to bears in Bulgaria (MCP100% and Kernel 99% isopleth for home ranges and Kernel 50% isopleth for core areas, Gavrilov et al. 2015) and Sweden (MCP95%, Dahle et al. 2006) and comparable to those reported in Italy (MCP100% and Kernel 95% isopleth for home ranges and Kernel 50% isopleths for core areas, Preatoni et al. 2005). The larger home range sizes from our study could be due to external factors such as human disturbances due to logging activities, heterogeneous landscapes or food availability. In particular, the home range sizes may have been influenced by the presence of supplementary feeding locations (3–5/100 km² in study area, personal estimation). Bear daily displacement length comparisons revealed minor differences between seasonal movements: the Winter season displacement distances were smaller compared to the Hyperphagia season (Figure 6). The daily mean distance, estimated in our case, corroborates those obtained in other studies – median daily distance of 1500 m in Croatia (Huber and Roth 1993) and averaged 2450 m in Greece (Mertzanis et al. 2005).

Seasonally, Hyperphagia resulted in increased home ranges and daily movements in all individuals. During the Hyperphagia season, we recorded the lowest altitude for an adult female and a highest variability of altitude between individuals, showing a tendency to seek out food resources in different types of habitats varying along an altitudinal gradient (Pop et al. 2018). Considering both the daily movement and altitude results, we observed a variability of the daily, seasonal and altitudinal movements of brown bears on relation to the seasonal and altitudinal natural food resource availability. The greater anthropogenic food availability at lower altitudes, such as orchards or crops, might also influence the brown bear distribution (Pop et al. 2012), especially during the Hyperphagia season. Seasonal movements of brown bear in the Carpathians should be analysed in relation to seasonal changes in bear diet, approach often addressed in other studies (Stofik et al. 2013, Ciucci et al. 2014) to explain changes in brown bear movements.

As the main limitation of the study was related to the small numbers of bear females (4) and subadults (5), some of our results should therefore be interpreted with caution (Preatoni et al. 2005). Using a larger dataset and considering the seasonal and altitudinal gradient of the food availability (Roellig et al. 2014), may result in differences between seasonal movements and/or between genders. Future brown bear spatial ecology studies in the Romanian Carpathians should consider both external (e.g., food availability, predation risks, presence of mating partners) and internal factors (e.g., health, age, reproductive stage) (Nathan et al. 2008, Martin et al. 2013) recommended using a landscape approach (Di Minin et al. 2016).

In summary, our study, using GPS telemetry, highlights the complex spatial ecology of the brown bear in the Carpathians, with home range sizes larger than those estimated in other European brown bear populations and daily movements that vary by season and within a broad altitude range. Human disturbance caused by traditional activities such as logging, hunting, agriculture, could not be considered when describing the movements, but it represents a key factor influencing brown bear movement and habitat selection (Martin et al. 2010), and should be considered in further studies. Notably, our study supports the implementation of brown bear monitoring at a regional scale, rather than focusing on GMUs as the monitoring unit (Popescu et al. 2016). As brown bears may use multiple GMUs annually or during a single season, a regional approach to monitoring based on remote cameras and track counts (Popescu et al. 2017) or non-invasive DNA techniques (Proctor et al. 2010) is likely to yield better results and will require coordination between multiple adjacent GMUs. Additionally, conservation initiatives should cover large areas, which seems to be difficult in Romania given the tendency of conservationists to work at a local scale (Nita et al. 2016). This study provides important information for future brown bear research and conservation, such as habitat selection studies, habitat connectivity and population estimates for Romania’s brown bear population.

The research was supported by a grant of the Romanian National Authority for Scientific Research (www.uefiscdi.ro), PN-III-P2-2.1-PED-2016-0568. We thank our colleagues from ACDB, Vrancea, Covasna and Harghita EPAs, WWF Romania, Buzau County Council and to game wardens for the efforts made during the trapping and monitoring activities. The bears were fitted with GPS collars within the projects: LIFE08 NAT/RO/000500 LIFEURSUS, Protecting and promoting the biodiversity in the ROSCI0190 Penteleu and ROSCI0229 Siriu and Open Borders for Bears between Romanian and Ukrainian Carpathians. We thank Diana Zlatanova, Gabriel Chisamera and an anonymous reviewer for their valuable comments and suggestions on the manuscript.