Home Range of Wolves in Bialowieza Primeval Forest, Poland, Compared With Other Eurasian Populations

Some very important studies are being conducted on the Bialowieza wolves, and this one is of particular interest as wolf populations begin to recover in various parts of Europe. There isn't much prime wolf habitat left in that part of the world, so the carrying capacity of certain areas, which is (at least partially) determined by the pattern of home range use, is of keen interest. Another important element here: the maintenance of prey populations, since prey biomass directly affects pup survival, pack size, home range, and overall numbers of a wolf population -- JM

Pattern of space utilization by wolves (Canis lupus) has been intensively studied in North America but rarely in Eurasia. In southern Europe, few telemetry studies have been done in marginal wolf habitats. Numerous investigations on wolves in the former Soviet Union rarely were focused on accurate estimation of home ranges of wolves. Scarce data offer such diverse information that few conclusions or predictions for management seem possible. Reported home ranges of wolves vary from 16 km2 in Portugal to -900 km2 in Spain, northwestern Russia, and Finland.

We studied use of space by wolves in Bialowieza Primeval Forest (BPF) in the Polish-Belarussian borderland, a large and relatively natural woodland harbouring a multispecies community of ungulates and predators. The study area was on the westernmost limit of the continuous geographic range of the wolf in lowland Europe. Our objectives were to: 1) assess pack size and density of wolves, 2) estimate the size of home ranges and describe seasonal variation in use, and 3) assess the pattern of home-range use. We also reviewed available data on home ranges of Eurasian wolves and attempted to identify factors that influence variation in size.

Currently, 40% of BPF (595 km2) belongs to Poland and 60% (875 km2) belongs to the Belarus Republic. Since 1981, the Polish and Belarussian parts of BPF have been separated by a border fence built by the Soviets along their state border. Most of the Polish part of BPF is a commercial forest exploited for timber and undergoing game management. Logging is done by means of small clearcuts and selective cutting of large trees. Clearcuts are replanted, usually with one or two tree species (pine, spruce, or oak). These changes in the forest structure discernibly affect ecology of wolves and ungulates. A small part (47 km2) of BPF has been strictly protected since 1921 as the Bialowieza National Park (BNP). Neither timber exploitation nor hunting is allowed in BNP It has been a Man and Biosphere Reserve of the United Nations Environmental, Scientific and Cultural Organization since 1977 and a World Heritage Site since 1979. In 1996, BNP was enlarged to 100 km2. The entire Belarussian part of BPF has been protected since 1945, and in 1991, it was given the status of a State National Park. Forests in BPF in Belarus have not been exploited for timber; only dead and dying trees are removed. Since 1993, the whole Belarussian part of the forest has been recognized as a Man and Biosphere Reserve.

The BPF harbours a rich community of ungulates: European bison (Bison bonasus), moose (Alces alces), red deer (Cervus elaphus), roe deer (Capreolus capreolus), and wild boar (Sus scrofa). The red deer is the most important and preferred prey of wolves. Large carnivores are represented by wolf and lynx (Lynx lynx). Since 1989, wolves have been protected in the Polish part of BPF They are persecuted in the Belarussian part; in 19801993, an average of 16 wolves were shot there annually, which made up 80% of the estimated winter numbers.

....Field procedures.--In the Belarussian part of BPF, data on numbers of wolf packs and pack sizes were obtained by snowtracking. After a new snowfall, snowtracking on all accessible forest-compartment (1,066 by 1,066 m) lines was conducted twice, usually on two consecutive days. Tracks of wolves crossing lines and their directions were noted. An attempt to count the number of wolves in a pack was made by following their tracks. All tracks were mapped and, by drawing reconstructed routes of wolves' movements, sites of daily rest were determined (i.e., forest compartments where a track went into but not out of it). Observations of wolves and their tracks also were noted during any field work and used as auxiliary data. All reports of hunts for wolves were collected and analyzed. In the Polish part of BPF spatial structure of the wolf population was studied by telemetry and snowtracking. Four female wolves belonging to two packs were livetrapped, radiocollared, and followed from March 1994 to September 1996....Sex was determined, and approximate age (yearling or adult) was estimated on the basis of date of capture, body mass, and tooth wear. Wolves were equipped with radiocollars. We attempted to locate radiocollared wolves 5 days/week by following forest roads by vehicle or bicycle....Because of the relatively short range of transmitters ( 1-3 km on the ground) and large home ranges of wolves, we succeeded in locating radiocollared animals in 78-92% of our attempts to find them.

We used the minimum-convex-polygon (MCP) method (White and Garrott, 1990) to estimate size of home ranges of wolves during the entire period of radiotracking and size of their home ranges in shorter periods (seasons and two months). For those calculations, all radiolocations from a relevant period were taken. Kernel methods (Worton, 1989) were used to analyze patterns of home-range use. For this method, from the entire set of radiolocations for a given period, 3 locations/24 h were taken whenever available: 1) a location in a daily resting place, 2) a location when wolves rested at night, and 3) a location most distant from the resting site used on the previous day....

Literature on sizes of home ranges of Eurasian wolves was reviewed. Data selected for comparisons fulfilled the following criteria: 1) values of home-range size given by authors came from real packs or individuals, 2) territorial status of a wolf or pack was certain (nonterritorial single wolves were not included), and 3) radiotracking was conducted for -6 months and snowtracking for - 1 winter season. In the latter case, maps from original papers were scanned, and sizes of home ranges were computed as MCP encompassing all mapped tracks and routes. Wherever available, pack size was given to check its possible influence on size of territory. Fairly undisturbed established populations were set apart from colonizing ones.

Number and density of wolves.--In 1993-1996, the whole BPF was inhabited by six to seven packs of wolves, each comprising from two to seven wolves. Density of wolves in late winter was 1.51.9 individuals/100 km2. There were considerable differences in density of wolves and average pack size between the Belarussian and Polish parts of BPF, resulting from different human attitudes towards wolves (control versus protection). In the Belarussian part of BPF, snowtracking evidenced only three packs in the end of winter in 1994-1995 (in the northeastern part the census was not conducted) and four packs in winter of 1995-1996. At least five wolves were shot in the Belarussian part during each of the 2 winters, which constituted 30-40% of the early winter numbers of wolves. During the 2 winters in the Belarussian part, mean size of a wolf pack was 2.7 and 3.2 individuals and densities of wolves were 0.9 and 1.5 individuals/100 km2, respectively. The Polish part of BPF was inhabited by three packs in 1994-1996. Average pack size was four to five wolves. Late-winter density of wolves ranged from 2 to 2.6 individuals/100 km2. In winters 1994-1995 and 1995-1996, wolf packs in the Polish part of BPF were larger than those in the Belarussian part. Undisturbed wolves in the Polish part of BPF maintained a more stable spatial structure than those in Belarus. Observations from the Polish part of BPF indicated a significant variation in social bonds within a pack between spring-summer and autumn-winter. In summer, wolves usually moved alone or in pairs (65% of observations). There were only a few observations of the whole families in late summer. In winter, single wolves and pairs made up only 38% of observations, and the majority of observed or snowtracked groups (51%) consisted of four or more wolves.

Size and use of home ranges.--In 1994-1996, four female wolves belonging to two Polish packs were radiotracked. During the first 3 months of telemetric observations the area used by radiocollared wolves increased rapidly. After 6 months of radiotracking, home ranges of two adult females were 53 and 70% of their total home ranges. After 9 months, the increase of area used by wolves was low. Thus, a reliable estimation of home-range size of wolves required 9-12 months of intensive radiotracking.

Home ranges of radiocollared wolves calculated for the whole period of radiotracking....ranged from 173 to 294 km2 . Home ranges estimated by 95% MCP (excluding out-liers) for three female wolves comprised 83-89% of their total home ranges. The 95% MCP of the fourth female covered 48% of her total home-range area. Core areas of radiocollared wolves, comprising 75% and 50% of locations, were calculated by MCP and Kernel methods. For all wolves, 50% of all radiolocations fell into small core areas of 11-23 km2, or 5-13% of the total home range. As many as 75% of radiolocations found wolves in somewhat larger areas of 31-73 km2, or 11-36% of the total home ranges. Thus, wolves used their ranges unevenly. Core areas were always located in regions of BPF that included no permanent human settlements and comprised extensive patches of inaccessible forests (bog alderwoods and swampy forests of pine, spruce or birch). In both packs, core areas were naturally delimited by rivers and were located in parts of BPF that were least penetrated by people.

Use of core areas of home ranges stemmed from two factors. First, breeding dens were located there, and the pack's activity was concentrated around the den when offspring were small. Secondly, a majority of diurnal resting sites used by wolves year round also was located in core areas. Packs hunted both in core areas and peripheral parts of their ranges, but during a several-hour rest during the day, they usually retreated to core areas of their large home ranges. Areas calculated for locations of wolves in their daily resting sites (95% MCP) covered 50-91 km2, or 32-60% of the comparable (95% MCP) home ranges.

Temporal variation in size of wolf home ranges.--Home ranges used in spring-summer and autumn-winter varied from 99 to 271 km2. Size of home range of one pack in Poland varied nearly three fold among years, but that of the other pack remained fairly stable. However, average seasonal sizes of ranges of the two packs did not differ; they were 170 and 167 km2, respectively. There was minimal, if any, overlap of ranges of the two neighboring packs (3% in spring-summer 1995 and 1% in autumn-winter 1995-1996). When we concurrently radiotracked two wolves belonging to one pack (in autumn-winter 1995-1996), their ranges based on individual movements overlapped 95%, indicating that each was representative of the pack's home range.

Reproductive status determined the area used by female wolves. The two adult females gave birth to young in early May. During 2 months prior to parturition, the area used by females decreased by an average of 20% compared with their mid-winter ranges. In the first 2 months of pups' lives (May-June), females stayed in a small area around the breeding den (130 km2, or ca. 13% of mid-winter ranges). The area used by reproducing females increased in July-August. We synthesized data of 19 home ranges of wolves throughout Europe .... Home ranges of wolves increase from 80-240 km2 in southern Europe to 415-500 km2 in northern Europe. Multiple regression analysis revealed that two variables, latitude (L) and status of the wolf population .... explained 65% in the variation in the size of home ranges. From 42 to 680N, territory size of wolves grew with increasing latitude. At a given latitude, home ranges of wolves were larger in low-density colonizing populations and smaller in saturated ones....When we excluded two small packs of two and three wolves that were tracked in northern Sweden, home ranges of all other European packs were not related to pack size.

Based on our results and review of literature on wolves in Europe, we identified two sources of variation in size of home ranges of wolves. Apparent variation emerged from methodology and real variation resulted from seasonal and social changes in the life of a wolf pack. A crucial source of variation was the duration of radiotracking -- the longer the radiotracking, the larger the home range. Six to eight months of intensive radiotracking was the shortest time needed to reveal the minimum-reliable size of a home range. Moreover, to compare ranges of various packs, one needs to standardize time of tracking. If wolves were tracked for <6 months or radiocollared individuals with different tracking times simply were listed together, conclusions could be flawed seriously. For instance, the smallest reported home ranges of wolves of 16-66.5 km2 in Portugal come from data that were collected during only 3-8 (on average 5) months. From data presented by Pereira's team, we calculated that size of home ranges in km2 was positively related to the radiotracking time in months....

We found that radiotracking of wolves needs to be conducted during night as well as during daylight. Radiotracking during the day usually located wolves at their resting sites, which were concentrated in core areas of their home ranges. In BPF, size of home range estimated from distribution of daily resting sites covered only one-half of the total ranges. Thus, if in a given area wolves are active at night, it is necessary to gather radiolocations at night. In our study, continuous radiotracking over several 24-h periods revealed long but short-lasting excursions by wolves to hunt prey during the night.

Knowledge of the social status of radiocollared wolves also was important in assessment of home-range use. Social bonds in the pack changed seasonally, and size of area used by various individuals throughout the year varied greatly. During May-June, non-breeding females moved over ca. 75% of their winter territories, but breeding females stayed temporarily in only 10% of their winter ranges. Other European studies confirm that social status of wolf is an important factor of variation of home-range size. In Spain, a juvenile wolf moved over a small range of 100 km2, two adult males increased their ranges during mating season (291-568 km2), and a female that lost her litter and territory roamed throughout the territories of other wolves and covered 892 km2.

Comparison of data from various regions in Europe showed that there are two other sources of variation in the size of home ranges of wolves: latitude and status of the population....Voskar (1994) reported, albeit with no information on methods used, that home ranges of wolves in montane regions of Slovakia were larger in years of low densities after several years of persecution than in years after the wolf population recovered.

We propose that the major factor underlying latitudinal variation in home-range size of wolves is the occurrence and density of the red deer, a preferred prey of wolves. The continuous range of red deer in central Europe and the Caucasus Mountains coincides with small home ranges of wolves (80-200 km2). This relationship needs quantitative examination on both local and Eurasian scale when more data from various ongoing projects on wolves are available.

INCLUDES

Figure 1: Number and spatial distribution of wolf packs...in Bialowieza Primeval Forest (BPF) in winters 1994-95 and 1995-96.

Figure 2: Frequency of single wolves, pairs, and groups of various size in spring-summer and autumn-winter in the Polish part of BPF in 1993-1996.

Figure 3: Increase in the estimated size of home ranges of four radiocollared wolves in BPF (1994-1996) relative to length of radio-tracking.

Figure 4: Seasonal changes in home ranges of female wolves radiotracked simultaneously in the Polish part of BPF in 1994-1996...

Table 1: Characteristics of wolf population inhabiting BPF.

Table 2: Home range of four radiocollared wolves in BPF in 1994-1996...

Table 3: Bimonthly changes in the area...used by female wolves in BPF in relation to their reproductive status.

Table 4: Summary of home ranges of Eurasian wolves.

References: 29