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1 December 2007 Spatial and Social stability of a Eurasian lynx Lynx lynx population: an assessment of 10 years of observation in the Jura Mountains
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Abstract

A total of 18 Eurasian lynx Lynx lynx were radio-tagged between March 1988 and June 1998 in the Swiss Jura Mountains, and during 1995-1997 eight animals were radio-tagged on the French side of the mountain chain. Adult males occupied larger long-term home ranges than adult females (283 km2 vs 185 km2). Neighbouring males shared 7.3% of their home ranges and females 0.2%. The mean distance between males and females living in the same area for fixes taken the same day was 10.94 ± 8.61 km, underlining the solitary character of the species. Consecutive individual annual home ranges overlapped 71.7 ± 7.3% for females and 77.5 ± 7.9% for males, indicating high spatial stability over time. In the Swiss study area, two adult animals were followed for seven and nine years, respectively, and another two lynx were observed in the study area for nine years. Range size did not vary across three distinct periods, P1-P3, but the sex ratio did. Generally, males covered the ranges of 1-2 females, but during the second period, P2, the range of a single male overlapped with those of six females. Dead females were all immediately replaced, but dead males were not. Two poached males were only replaced after three and five years, respectively. Population density, ranging within 0.7-0.8 adult resident lynx/100 km2, did not vary significantly over time in Switzerland. Including kittens and subadults, the density was 1.1-1.6 lynx/100 km2. Our study in the Jura Mountains indicated that there is long-term stability in the social and spatial structure of the lynx population, but this stability was temporarily disturbed by the lack of adult resident males.

Large carnivores are long-lived animals with slow turn-over rates (Gittleman 1986), and scientific studies, generally running for only a few years, allow researchers to study a small time window in the development of populations only. To understand the functioning of populations and to be able to develop effective conservation strategies, it is imperative to know more about the dynamics of such populations during a wider time window. The interpretation of the status and conclusions regarding the conservation will depend on the time frame studied (Pelton & van Manen 1996). We reviewed the Journal of Wildlife Management from 1980 through 1995 for the survey periods of wildlife studies. Of 1,398 publications, 80% dealt with ≤ 5 years, and only 8% covered ≥ 10 years. Furthermore, long-term studies on large and medium-sized cats are relatively sparse. Prominent among others are projects on lions Panthera leo in the Serengeti and the Ngorongoro Crater in Tanzania since the early 1960s (Schaller 1972, Packer et al. 1991), on tigers Panthera tigris in Royal Chitwan Nation Park, Nepal, from 1977 until 1987 (Smith 1993), on cougars Puma concolor in the San Andreas Mountains of New Mexico from 1985 until 1995 (Logan & Sweanor 2001), on Iberian lynx Lynx pardinus in the Coto Doñana in southwestern Spain since 1983 (Palomares et al. 2000, 2001, Ferreras et al. 1997), and on Canada lynx Lynx canadensis, studied in the Northwest Territories from 1989 until 1993 (Poole 1995) and the Yukon Territory from 1986 until 1994 (Slough & Mowat 1996).

Eurasian lynx Lynx lynx are medium-sized cats, growing as old as 15-17 years in the wild (Breitenmoser-Würsten et al. 2007). The species' spatial organisation has been studied in Norway (Andersen et al. 1998, Sunde et al. 2000), Sweden (Andrén et al. 1997), Norway and Sweden (Linnell et al. 2001), Poland (Jędrzejewski et al. 1996, Schmidt et al. 1997) and in the Swiss Alps (Haller 1992, Breitenmoser & Haller 1993, Haller & Breitenmoser 1986, Breitenmoser-Würsten et al. 2001). All of these studies had survey periods of 3-4 years, with very few individuals surveyed for > 2 years, and came to quite different conclusions in regard to territoriality and social and spatial stability. The differences could be related to the methods used or the environmental conditions in the study areas, but they could also have arisen due to the narrow time windows into a changing world. Three studies on lynx in the Swiss Alps, performed in an identical environment using the same field techniques, revealed very different levels of population status (Haller 1992, Breitenmoser & Haller 1993, Breitenmoser-Würsten et al. 2001).

We had the unique chance to work for 10 years from 1988 until 1998 in the Swiss Jura Mountains, which allowed us to study the long-term aspects of the land tenure system and the social structure of the lynx population. Another study was conducted in the adjacent part of the French Jura Mountains during 1995-1997; in this study additional data on the spacing behaviour of lynx were collected. All animals followed in these two studies belonged to the same lynx population. In this paper, we present the combined data sets and address the following aspects concerning the dynamics of the lynx population: 1) home-range size and overlap, 2) spatial and social organisation and its dynamics, and 3) development of the population density.

Material and Methods

Study Area

The Swiss study area encompassed the part of the Jura Mountains in the cantons of Neuchâtel and Vaud and extended along the first chain of the Jura Mountains into France south to Fort de Vaucluse. The intensive study area where adult animals were regularly located covered 1,300 km2. A detailed description of the Jura Mountains is presented in Breitenmoser et al. (2007). The French study area was located in the southeastern part of the Département du Jura and covered 1,100 km2; for more details see Vandel (2001). The two study areas bordered onto each other along the Mijoux valley, behind the first chain of the Jura Mountains west of Geneva. About half of the Jura Mountains are covered by forest (Breitenmoser et al. 2007), deciduous trees along the slopes and coniferous forest on the ridges. The Swiss study area ranged in elevation within 484-1,718 m a.s.l. (Crêt de la Neige), the study area in France within 246-1,226 m a.s.l. The main prey of lynx in the Jura Mountains is roe deer Capreolus capreolus and chamois Rupicapra rupicapra (Molinari-Jobin et al. 2007, Breitenmoser et al. 2007).

Study Population

Lynx went extinct in the Jura Mountains during the 18th century. The last evidence of lynx was an animal killed near Lignerolle (Canton of Vaud) in 1830 (Schauenberg 1969). Lynx were brought back to the mountain chain through a reintroduction project in Switzerland in the 1970s (Breitenmoser & Baettig 1992). Authorised releases of four individuals originating from Slovakia took place in 1974 and 1975 in the Swiss Jura Mountains. Additional animals were released in clandestine events resulting in a maximum founder population of 8-10 lynx (Breitenmoser et al. 1998). The increasing population spread into France, mainly during the 1980s. Today, the French part constitutes the core area of the Jura population (Vandel & Stahl 2005). During our study period, all suitable habitat had not yet been occupied, in particular areas north and northwest of the study area had not been permanently occupied (Capt 2007). The lynx population in the Jura Mountains is still isolated from the populations in the Alps and Vosges Mountains (Zimmermann & Breitenmoser 2007).

Capture and Tracking

Lynx were trapped with foot snares installed around lynx kills during 1988-1997 in Switzerland and during 1995-1997 in France. The survey period ended in June 1998. Additionally large double-door box-traps were placed on frequently used paths in Switzerland during the winter months. One lynx in France was caught with a foot snare set on a trail regularly used by lynx. All traps were equipped with an alarm system, allowing for remote control. Animals caught in Switzerland were immobilised with a Ketamin/Xylazin mixture until 1992. From 1993 onwards, we used 0.1-0.15 mg/kg methetomidin (Domitor®) and 0.8-1 mg/kg ketamin (Ketasol®) for anaesthesia, and 0.5-0.75 mg/kg atipamezol (Antisedan®) for reversal. Lynx caught in France were immobilised with Zoletil. Animals were classified as 1) juveniles when they were still with their mother (up to 10 months of age; Zimmermann et al. 2005), 2) subadults during their dispersal until they established a permanent home range (Zimmermann 1998) and 3) adults thereafter. Residents were adult animals occupying their own territory (a home range stable over several years excluding other animals of the same sex), and floaters were non-resident adult lynx. We tried to capture young lynx while they were still with their mothers, i.e. during February-April, so that we would be able to follow them during their dispersal (Zimmermann et al. 2005). In this paper, we include only lynx who later settled down as resident adults. Lynx were fitted with radio-collars weighing 220 g (Wagener, Cologne, Germany). From adult animals in Switzerland an incisor was removed for age determination using the cementum-annuli method (Jensen & Nielsen 1968). For animals that died during the study period, the age determination was repeated on a canine for more reliable results (Kvam 1984).

Animals were located by ‘homing-in’ (White & Garrott 1990) with a precision of 1 ha or by drawing the bearings on a topographical map without approaching the lynx, yielding locations with an accuracy of 1 km2.

Spatial and Statistical Analyses

For spatial analyses, we only accepted one location per 24 hour period for each lynx to avoid autocorrelation. We defined as total range the convex polygon of all locations according to the minimum-area method of Mohr (1947). To eliminate outliers, i.e. locations apparently outside the normal use, we applied the method described in Breitenmoser et al. (1993), where a stem-and-leaf analysis (Tukey 1977) was performed on i0909-6396-13-4-365-e01.gif, where DCent was the distance to the arithmetic centre, and DLocs the mean distance to all other locations. An observation was identified as an outlier if its outside value was larger than H75 + 1.5*HS, where H75 is the upper hinge and HS the hinge spread. We then defined as home range the convex polygon of all locations excluding the outliers.

To describe range use, we chose the 95%-kernel area (Worton 1989, Seaman & Powell 1996). For the smoothing factor H, we applied the user-defined option, because the Ad Hoc or Least Squares Cross Validation (LSCV), did not produce satisfying results, as the distribution of locations and the shape of the home ranges did vary considerably between animals. Additionally, we calculated annual home ranges for adult animals present for at least 10 months in any given 12-month period.

For all range analyses, we used the Animal Movement Analysis Extension for Arc View 3.1 (Esri 1996, Hooge & Eichenlaub 1997). The increment analysis was performed within Arc View using a script (U. Müller, pers. comm).

Percent overlap of total ranges and home ranges between animals A and B was calculated as:

i0909-6396-13-4-365-e02.gif
We calculated the different range-use models for the entire survey period of each animal and called this long-term home ranges. Additionally, we divided the 10 years of observation into four periods, according to significant changes in the spatial behaviour of the observed animals as well as the loss and appearance of new animals (Fig. 1). Period 1 (P1) included the years 1988-1991, Period 2 (P2) the years 1992-1994, Period 3 (P3) the years 1995-1997, and Period 4 (P4) the year 1998 until the end of June when the survey was terminated. As the last period is considerably shorter than the previous periods, data from this period were only used to show changes in spatial behaviour of animals that were also followed in previous periods. For comparison between sexes or time periods, we only included animals that were followed for > 1 year.

Figure 1

Distribution of home ranges (i.e. total range excluding outliers) of adult resident lynx in the Jura Mountains for the four observation periods P1-P4 (A-D). Ranges of males are delineated by solid lines, and those of females are dark grey. The pale grey area in C) indicates the home range of FMAYA who remained in the home range of her mother FAIDA. Dashed lines indicate the border between France and Switzerland, light grey shows major lakes, and lines with arrows indicate migration routes and directions of adult animals. Black dots show the locations where FAMBA, MAMOS and MTARO were found dead in 2001, 2002 and 2005, respectively.

i0909-6396-13-4-365-f01.gif

For the density estimation of adult animals in Switzerland, we used the radio-collared lynx and collected all available information of individuals not radio-tagged. If signs of presence of a lynx could not be assigned to one of the radio-collared animals, efforts were intensified to trap this individual. If an animal died or disappeared, trapping efforts were intensified as well to collar the successor as quickly as possible. All observed total ranges together defined the reference area for the density estimation. For gaps with no information, we measured the surface and defined the number of animals fitting in there based on the mean home-range size and overlap of the respective sex (Mace & Waller 1997). For the total density, we added the mean number of kittens and the number of subadults per female in the study area during the winter for the respective numbers of adult females present. These two figures were taken from Breitenmoser-Würsten et al. (2007) and are based on the survival rates in these two age categories.

Results

Observed Lynx and Survey Period

A total of 27 lynx were caught 47 times from March 1988 until the end of 1997; 18 lynx were equipped with radio-collars in Switzerland and so were eight in France (Table 1). Of the animals captured, nine were adult males, 10 were adult females, one was a subadult male and six were subadult females. Adult males were significantly heavier than females (20.8 kg, SE  =  0.6, vs 17.2 kg, SE  =  0.4; t-test: P < 0.001).

Table 1

Data on the 26 lynx radio-tracked in the Jura Mountains during March 1988 - June 1998. Lynx captured in France are marked with * and animals that were still under control at the end of the survey period in June 1998 are marked with **. Animals marked with 1 were captured as subadults, followed during their dispersal and as resident adult lynx. FAMBA was poached in the study area in November 2001; MAMOS died in August 2002 in the study area due to an accident ; MTARO died in 2005 at the edge of his 1998 range, and FMAYA was last observed in the study area in January 2003.

i0909-6396-13-4-365-t01.gif

Adult animals were observed for a mean of 2.2 years (N  =  25, range: 0.4-6.4 years; Table 2). Only three animals had a survey period of < 1 year. For the remaining 22 lynx the mean survey period was 2.5 years (1.1-6.4 years). The survey period for males and females was not different (Mann-Whitney: U  =  81, P  =  0.610). For the animals MTARO and FAMBA, the observation by telemetry was interrupted because of a breakdown of their radio-collars. Both animals were observed within their home ranges several times while their radio-collars stopped functioning. They were recaptured within their ranges after two and a half and three years, respectively (see Table 2). A total of 10,605 radio locations were included in the range analyses for adult animals.

Table 2

Survey period for 26 adult lynx in the Jura Mountains during 1988-1998. The numbers beneath the years indicate quarterly periods (1-4). Lynx marked with * were caught while they were still with their mothers and then followed by telemetry during their dispersal (d; Zimmermann 1998) and as adults occupying their own home ranges (X). † indicates death of the animal and ? indicates that fate of animal is unknown. c indicates collar breakdown or battery failure, lc a lost collar, o that the animal was observed after the collar stopped working, m that the animal moved far off the study area, e that the survey of the animal ended, r that the animal was recaptured, rm that the animal was removed because of excessive damage to livestock (Stahl et al. 2001).

i0909-6396-13-4-365-t02.gif

We aimed to locate each adult lynx at least twice a week. However, we were not able to fulfil this aim for all animals (Table 3). An exceptionally low rhythm was applied to animals that had moved off the study areas (FWINA, FNADA and MRICO for Switzerland and MFAD9 for France) and animals that were still surveyed after the intensive study period had ended (e.g. FFAD8 in France; see Table 1).

Table 3

Home-range size of 26 adult lynx in the Jura Mountains during the periods P1-P4. Location rhythm is expressed as survey period/number of locations. Total range is expressed as 100% minimum convex polygon and home range as restricted convex polygon excluding excursions. Dbdl gives the distance between daily locations and N  =  sample size for Dbdl. FKIRA was present during limited time spans until the appearance of FLORA in February 1990, after which FKIRA shifted her home range (Breitenmoser et al. 1993). After the death of her mother FLORA in January 1993, FROYA took over her home range. FAIDA was present in her first home range until 31.12.1996 and in her second home range in 1997.

i0909-6396-13-4-365-t03.gif

Home-range Size

Long-term total ranges were not different for adult males and females (median 465 km2 and 280 km2; Mann Whitney: U  =  27, P  =  0.072), but males had significantly larger home ranges than females (median 283 km2 and 185 km2; Mann-Whitney: U  =  16, P  =  0.010; Table 4). With 1,744 km2, MTARO had an outstandingly large long-term total range, and, with 672 km2, also a very large long-term home range. At the other end of the scale was MFSA3, with a total range of only 145 km2 and a home range of 113 km2. This young male had specialised in killing sheep and was therefore removed from his territory in 1998 (Stahl et al. 2001). The small home-range size of this animal caused the lack of significance in total range size between the sexes. All other males that were surveyed for at least one year by telemetry had higher and fairly similar values (see Table 4). If MFSA3 was excluded, the total ranges of males were larger than those of females (Mann Whitney: U  =  14, P  =  0.016).

Table 4

Long-term ranges of adult lynx in the Jura Mountains. Location rhythm is expressed as survey period/number of locations. Total range is expressed as 100% minimum convex polygon. Home range is expressed as restricted convex polygon (outliers excluded). a only animals that were followed for at least one year were included in the medians and for b1-b7 the ranges were computed only during their respective resident phases (dispersal excluded): 1 01.06.1996 - 31.12.1997; 2 01.01.1992 - 31.10.1994; 3 01.012.1994 - 21.02.1995; 4 01.06.1992 - 15.02.1995; 5 13.10.1992 - 24.11.1994; 6 1998; 7 01.12.1996 - 31.12.1997.

i0909-6396-13-4-365-t04.gif

We performed a multiple regression analysis with the dependent variable home-range size and the independent variables sex, body weight, number of locations and survey time. These four factors explained 75% of the variance in the size of lynx home ranges (N  =  15; P  =  0.005). The values of the male MTARO were excluded, as he was identified as an outlier (leverage 0.591-0.674; studentised residual 3.361-6.872). In the stepwise backward elimination, sex was the remaining variable explaining 66% of the variance (P < 0.001). The next important variable was body weight (r2  =  0.39, P  =  0.012). Number of locations and survey time were not significant.

Looking at the total range during the three periods P1-P3 (see Table 3), males roamed during all periods over larger total ranges than females (Mann-Whitney: U  =  22, P  =  0.045). The same was true for home ranges (Mann-Whitney: U  =  19, P  =  0.017; see Fig. 1 and Table 3). For both sexes, the range sizes did not vary across the three periods (Fig. 2 for home ranges; females: Kruskal Wallis: H  =  0.085 for total ranges and H  =  1.192 for home ranges, both P > 0.05; males: H  =  2.560 and H  =  3.271, respectively, both P > 0.05). The exceptional large range of male MTARO in Period 2 (see Fig. 1) did not influence this result for males.

Figure 2

Home-range size of adult females (grey lines) and adult males (black solid lines) for the observation periods P1-P4. The data are presented as box plots, with the centre line showing the median.

i0909-6396-13-4-365-f02.gif

The restricted polygon contained a larger proportion of the total number of locations for males (mean: 96.0%) than for females (mean: 91.1%; Mann-Whitney: U  =  14.5, P  =  0.006). The home range was 58.8% of the total range for females and 73.6% for males, respectively (Mann-Whitney: U  =  22.5, P  =  0.032). In females, these two proportions were positively correlated (r2  =  0.68, N  =  13, P  =  0.001), but in males they were not (r2  =  0.033, N  =  8, P  =  0.669). This demonstrates the different range use of the two sexes. Females have an outer circle that they use infrequently, whereas males regularly patrol the boundaries of their home ranges, and additionally some make short excursions into neighbouring territories, which are excluded in the restricted polygon. This can lead to a low value for the proportion home range over total range and still a high value for the ratio of the locations as these excursions can have a great impact on the total range, but not on the number of locations.

Overlap

The mean overlap of total ranges and home ranges of males and females living in the same areas was 49.6 and 51.5%, respectively. For females, the mean overlap with the resident male was 81% of their home range, whereas for the male home ranges, the mean overlap with the home range of a resident female was only 36%. Neighbouring females shared 16.7% of their total ranges and 0.2% of their home ranges, neighbouring males 16.2% of their total ranges and 7.3% of their home ranges, respectively. Additional to the females within their home ranges, males had access to 1-4 neighbouring females (see Fig. 1). The overlap with the total ranges of the neighbouring females was 21.3% and 5.4% with their home ranges.

There were two exceptions from these patterns. One concerned the males MFAD1 and MFAD2. They were living in the same area from April to early October 1995. Nevertheless, 24.7% of the locations of MFAD1 were within the home range of MFAD2. After the death of MFAD2, MFAD1 used this area more often, and 55.9% of his locations were in the former range of MFAD22  =  20.724, P < 0.001). The distance between the two animals when located on the same day was 11.80 km (SD  =  6.09 km, N  =  137, range: 0.90-31.77). Even though they had overlapping ranges, they clearly avoided each other. The second exceptions were the two females FAIDA and her daughter FMAYA described below.

Sociality

As a measure of sociality, or solitude, we used the distance between two individuals located the same day. Males and females living in the same area only met occasionally and were usually separated in space or time. They were 10.94 km (SD  =  8.61 km, N  =  2,793, 14 male-female pairs) from each other when located on the same day. We observed 75 meetings of male and female lynx; 52 (70%) of them during the mating season from mid-February to mid-April. On an additional 105 occasions, males and females were < 1 km apart. Neighbouring males were closer than 1 and 2 km only three and 11 out of 1,143 times, respectively. The mean distance between them was 25.23 ± 13.55 km. A similar pattern was observed with neighbouring females. On only seven and 14 out of 1,791 occasions were females found < 1 km and < 2 km apart, respectively. With 16.51 ± 7.04 km, the mean distance was smaller than the distance between neighbouring males, reflecting the higher density of resident females.

Home-range Use

The mean 95%-kernel area, calculated for animals that were followed for at least one year, was 119 km2 for females and 226 km2 for males (Mann-Whitney: U  =  11, P  =  0.003; see Table 4). The 95%-kernel area covered 41% of total range for females and 63% for males, which was not significantly different (Mann-Whitney: U  =  35, P  =  0.217). There was one exception in males, MTARO, whose 95%-kernel area covered only 18% of his total range. His total range was very large, but he used a core area comparable to those of the other males. In females, for FFAD5 and FFAD7, the 95%-kernel area constituted as much as 87 and 81% of their total ranges, respectively. For the other females, this value ranged within 20-65%. Without the three obvious exceptions, the difference in the share of the 95%-kernel area of the total range between the sexes would be significant (Mann-Whitney: U  =  8, P  =  0.006). For both sexes, there was no difference in the size of the 95%-kernel area across the periods P1-P3 (females: Kruskal Wallis: H  =  2.809, P  =  0.245; males: Kruskal Wallis: H  =  2.560, P  =  0.278).

Distance Between Daily Locations

Overall, male lynx moved significantly further than females (2.51 km, SE  =  0.11, vs 0.96 km, SE  =  0.04; Mann-Whitney: U  =  4.26 × 106, P < 0.001). This was also true for P1, P3 and P4 (all P < 0.001). An exception was MTARO. Although he occupied the largest range during P2, he did not move further than the females (P  =  0.988). There was a significant negative correlation between the distance between daily locations and the size of the total range and the home range of males, as animals with larger ranges moved less from day to day (total ranges: r2  =  0.638, N  =  11, P  =  0.003; home ranges: r2  =  0.874, N  =  11, P < 0.001). This was not the case for females (total ranges: r2  =  0.047, N  =  26, P  =  0.29; home ranges: r2  =  0.001, N  =  26, P  =  0.85). This could have been influenced by a difference in the location rhythm (mean number of days between locations) of the two sexes, assuming that males were harder to find because they roamed over larger areas, and the longer displacements could have been missed. Once they were found, they could have been located frequently. But the location rhythm was not significantly different for males and females (Mann Whitney: U  =  164.5, P  =  0.751), and did not differ across the four periods (Kruskal Wallis: H  =  6.465, P  =  0.091).

Stability of the Spatial Organisation

The increment analysis is a method to find out how long and how often animals need to be located to seize their entire home ranges. In both sexes, 95% of long-term home ranges were reached after a mean of 1.7 years (Mann-Whitney: U  =  47, P  =  0.876; Fig. 3) and 337 locations (Mann-Whitey: U  =  40, P  =  0.697). After one year of survey, females and males had roamed over a mean of 75% of their home ranges (Mann-Whitney: U  =  40, P  =  0.697). Exceptional low values were noted for FKIRA (46%) and MTARO (32%), indicating a shift of thehome ranges (Breitenmoser et al. 1993; see Fig.1).

Figure 3

Cumulative area of home range (i.e. total range excluding outliers) of adult male (A) and female (B) lynx in the Jura Mountains. For each additional location in chronological order, the convex polygon is plotted against time.

i0909-6396-13-4-365-f03.gif

Mean annual home ranges were smaller for females (126 km2, range: 53-259 km2) than for males (270 km2, range: 184-347 km2; Mann-Whitney: U  =  2, P  =  0.001). It covered a similar proportion of the long-term home range in both sexes (74% for females and 81% for males; Mann-Whitney: U  =  34, P  =  0.391). They did not vary across years for both sexes (females: Kruskal Wallis: H  =  1.257, P  =  0.939; males: H  =  5.977, P  =  0.308). The mean overlap of consecutive annual home ranges was similar for females and males (71.7 ± 7.3%, N  =  13, vs 77.5 ± 7.9%, N  =  6; Mann-Whitney: U  =  21, P  =  0.114), indicating a high stability of the spatial structure in the study area. The lowest values were observed for FKIRA with 55%, FROYA with 58% and MTARO with 58%, respectively. All three animals had shifted their home ranges during the survey period.

Stability of the Social Organisation

During P1, four resident females and three males were monitored in the Swiss study area. At the end of this period, four animals were dead, leaving the two adult females FAIDA and FLORA, and the adult male MTARO (Breitenmoser et al. 1993). The two poached males were not replaced until three and five years later (Table 5).

Table 5

Replacement of lynx that died or moved away from their home ranges. Lynx 1 is the disappearing, dying or shifting animal and Lynx 2 the newly appearing or intruding animal.

i0909-6396-13-4-365-t05.gif

During the whole P2, MTARO was the only resident male in the Swiss study area (see Fig. 1). During the mating season in 1993, he met with six different females, four of which were radio-collared (Breitenmoser-Würsten et al. 2007). The two females who had vanished at the end of P1 were replaced within a maximum of half a year (see Table 5). In the southwest, the adjacent female FELSA was trapped and radio-collared (see Fig. 1). The two subadult females FNADA and FWINA dispersed into France, where they established their own home ranges and reproduced for the first time in 1993. At the end of October 1993, FNADA left the home range that she had established in early 1992 and moved southwest (see Fig. 1), where she settled down at the edge of the Jura Mountains in 1994 (Zimmermann & Breitenmoser 2007). At the end of P2 and early in P3, FWINA and FROYA died (see Table 1).

Towards the end of P2, MTARO started to change his spatial behaviour. He did not use the northeastern part any more. In early 1995, the two males MAMOS and MMOMO were trapped and radio-collared in this area (see Table 5). MAMOS was born in 1993 as a son of MTARO and FAMBA (KORA, unpubl. data). The overlap of the total ranges of MAMOS with the former range of MMIRO as well as of the home ranges was 80%. The situation in P3 was similar to the situation in P1: three neighbouring males and the corresponding neighbouring females were living in the Swiss part of the study area (see Fig. 1C). In P3, additional animals were radio-collared in the study area in France (Vandel 2001; see Table 1). These lynx were neighbouring the already monitored animals in the southwest of the Swiss study area (see Fig. 1C). In 1996, the young adult male MRICO was trapped in the northeast at lake Neuchâtel. He was roaming over large areas. His origin was unknown and his social status remained unclear; probably MRICO was a floater, i.e. one of the rare non-resident adult males.

During P3, the long-term resident adult female FAIDA was replaced by her daughter FMAYA. FMAYA was born in 1995. She did not leave the maternal home range, as subadult lynx usually do, during their first year of independence (Zimmermann 1998), but stayed within the home range of her mother (see Fig. 1C).

The largest home range during P3 was occupied by MFAD1 (413 km2), who also had the largest 95%-kernel area (328 km2; see Table 3). MTARO had the largest total range (759 km2). His home range and 95%-kernel area have a bias, as he was less often located in the southwestern than in the northern part of his home range. As a consequence, the locations in the south were identified as outliers. He occupied the same area in the south during P3 and P2. The centre of activity (mean of X and Y coordinates of all fixes) only shifted 2.0 km.

During P4, the two males MTARO and MMOMO both shifted their range activities compared to P3 (see Fig. 1). MTARO moved his centre of activity 10.0 km to the west. After that, he spent most of his time in France, east of the Mijoux valley; only eight of 67 locations were still in Switzerland. MMOMO reacted on this and shifted his centre of activity 4.3 km to the southwest. MTARO had lost his two long-term mates FAIDA and FELSA. His range had overlapped with their home ranges for at least 7-8 years. The only female left in his old home range was his own daughter, FMAYA. They had met during the mating season of 1997, but FMAYA did not reproduce. The shift of his home range in 1998 gave MTARO access to at least two new females (FZAYA and FFAD8; see Fig. 1D). In 2005, his radio-collar was found at the edge of his range of 1998, so probably he had stayed in this area for seven years. The locations where FAMBA and MAMOS were found dead in 2001 and 2002 suggest that these two animals also had shifted their home ranges along the first chain of the Jura Mountains southwards (see Fig. 1D).

Population Density

For P1-P3, the density of adult resident lynx was fairly constant in the Swiss study area, varying between 0.7 and 0.8 lynx/100 km2 (Table 6). The reference area varied between 1,007 km2 and 1,297 km2. During P2 and P3, the Swiss study area reached further to the southwest than during P1 (see Fig. 1). Additional to the adults, we calculated 0.50-1.29 kittens per female and year, and 0.1-0.55 subadults per female and year during the winter. The total number of lynx in the Swiss study area was therefore 1.1-1.6 lynx/100 km2.

Table 6

Density estimation of resident lynx in the Swiss study area for the three periods P1-P3. The reference area was defined through the boundaries of all total ranges of the radio-collared animals. Marked lynx are radio-collared resident animals, unmarked lynx are resident animals that were observed or that were assumed to be in the area based on the social and spatial behaviour of the radio-collared animals. Densities are given in number of lynx/100 km2. The number of kittens/female and the number of subadults are from Breitenmoser-Würsten et al. (2007).

i0909-6396-13-4-365-t06.gif

Discussion

Spatial Structure

The observed social and spatial structure of the lynx population in the Jura Mountains confirms findings obtained in other telemetry studies on Eurasian lynx. The home-range sizes in the Jura Mountains for males (283 km2) and females (185 km2) were in between those reported from Poland and Norway, but they are comparable to those found in the Swiss Alps in the 1980s (Breitenmoser & Haller 1993). However, lynx home ranges observed in the northwestern Alps of Switzerland during the late 1990s (Breitenmoser-Würsten et al. 2001) were significantly smaller; males occupied on average only 169 km2, and females 100 km2, respectively. Range sizes computed might also depend on the period of time an individual was followed. The increment analyses revealed that we had reached the asymptotic value for most animals. Neither observation period nor number of locations influenced home-range size any further. In a study in Poland by Schmidt et al. (1997), where most animals were observed for 12-15 months, this was not the case, and, especially for adult males, long-term home ranges in reality may have been larger than the figures published (248 km2 for males and 133 km2 for females).

Home-range sizes of females in solitary felids depend on resources to rear the young, whereas males' range structure depends on the distribution of females (Eisenberg 1986). In central Norway, where ungulate density was 4-6 times lower than in the Jura Mountains, male lynx roamed over 1,906 km2 and females over 561 km2, respectively (Sunde et al. 2000, Molinari-Jobin et al. 2002). In Switzerland, the roe deer population seemed to have increased during the 10 years of observation (Molinari-Jobin et al. 2007). However, the lynx population did not increase in space or numbers during the study period (Vandel & Stahl 2005, Capt 2007), as one would have expected from other carnivore studies (e.g. Stander et al. 1997). Very likely, the mortality rate in lynx reached a level that, due to illegal killings, did not allow the population to grow further (Breitenmoser-Würsten et al. 2007). Additionally, the increase in the roe deer population was probably not significant enough to cause an important numeric response in lynx (Molinari-Jobin et al. 2007).

The overlap between neighbouring animals of the same sex was small and < 10%, underlining the exclusiveness of the home ranges (Sandell 1989). Only when new animals appeared, was the overlap temporarily larger until the situation was settled again. In the northwestern Swiss Alps, where a larger number of neighbouring animals were observed, the overlap was < 10% as well (Breitenmoser-Würsten et al. 2001). In contrast to these findings, Schmidt et al. (1997) found an overlap of 30% between males and 8-29% for females. The population observed in Poland experienced large turnover during the study period. This could, further to the relatively short survey periods of individual lynx, result in an overestimation of the overlap between animals of the same sex. We observed on several occasions that a newly arriving female initially had a big overlap with the resident female, which steadily decreased until the animals had divided up the area between them. In Iberian lynx, high overlap with newly appearing animals of the same sex have also been observed. In contrast to the Eurasian lynx, it was not uncommon that overlapping individuals were involved in fights which usually determined the end of the high overlap (Ferreras et al. 1997).

Males with large home ranges moved less from day to day than males with smaller ranges. A similar observation was made in the Swiss Alps. The male with the largest home range (M1 in Breitenmoser & Haller 1993) covered on average a straight line distance of only 1.133 km from day to day, whereas another male (M2), who occupied a home range of 275 km2, moved 1.821 km. The males observed in the Swiss Alps during 1997-2000 had a mean home-range size of 169 km2, and moved 3.527 km from day to day. Males with larger home ranges seem to use their range in a different way than males with smaller ranges, who control and mark their range boundaries on a regular basis (Dötterer 1992), probably as a consequence of the closeness of neighbouring males. During P2, MTARO was clearly no longer able to be constantly present along the borders of his territory, but as no obviously rivals were around, he did not need to be so. He may have switched to a different strategy, and instead of controlling the boundary he may have surveyed the females.

Social and Spatial Stability

Successors of vanished resident lynx occupied almost the same home ranges. However, the sex ratio was not stable. Dead females were in all cases quickly replaced, but dead males were not (see Table 5). The two resident males that died in the Swiss study area in 1989 and 1991 were not replaced until 1994/1995. During P1, we observed a low survival of male kittens and subadults (Breitenmoser-Würsten et al. 2007). This had consequences for the replacement of dead males. The two males appearing in 1995 were both young, one born in 1993, the other not much older. During 1989-1991, nine animals were removed in France as livestock raiders (four adult males, two juvenile males, one female and two of unknown sex; Stahl et al. 2001). The temporarily high mortality of (resident) males in the two study areas probably led to a lack of dispersers and a disturbed social structure in Switzerland. This allowed MTARO to meet with six females during the mating season of 1993. The lynx population in the Jura Mountains has been reintroduced with a small founder population (Breitenmoser & Baettig 1992). Dramatic changes in the sex ratio of a population can increase inbreeding considerably, and jeopardise genetic stability. Additionally, disturbance of the social structure may have a large impact on the breeding success of solitary carnivores like the lynx (Breitenmoser-Würsten et al. 2007).

In New Mexico, USA, researchers removed 71% of adult females and 60% of adult males of a cougar population, and investigated the reaction of the remaining animals (Logan & Sweanor 2001). The removal of neighbours of the same sex did not cause females to expand their home ranges. The prominent male in the treatment area, however, immediately expanded his range, obviously looking for new mates. These results correspond well with our observations of the reaction of MTARO after the loss of his two neighbours MPACO and MMIRO. Males try to maximise breeding opportunities and will adjust their home ranges in a direct response to the availability of mates and the presence of rivals. Females, on the other hand, need to secure the resources for successful breeding and will adjust their home ranges to prey availability. As demonstrated by the very low overlap between neighbouring females, they hardly have encounters with conspecifics.

Conclusions

The observation period of 10 years in the Jura Mountains has shown that there is a potential for long-term stability in the social and spatial structure of a lynx population. In the Swiss study area, four lynx remained in rather stable home ranges for 7-9 years, and successive individuals of the same sex occupied congruent home ranges. After a disturbance (loss of adult resident males), the pre-disturbance social and spatial setup was re-established, however, only after > 3 years. Anthropogenic losses brought the population out of balance, and the recruitment remained low for a few years. Natural mortalities cannot be influenced, and legal removal of problem animals is an important management tool to uphold local people's acceptance of the predator, but laws should be strictly implemented to prevent poaching. The lack of males can lead to a situation where, as in the Swiss study area, one male fathered many litters and all the cubs born in this area were half-sibs. The pronounced topographic and anthropogenic structure of the Jura landscape seems to promote spatial and, hence, social stability of the population, but it also seems to limit the flexibility of the land tenure system.

Acknowledgments

many people and institutions contributed to this study. We would like to sincerely thank them all for their contribution. A core team of motivated people collected the data in the field in Switzerland: Dr. M. Liberek, Dr. P. Kaczensky, M. Dötterer, M. Wölfl, S. Wölfl, J. Auer, D. Gétaz, R. Pensa, S. Roy, J.D. Horn, L. Hofer, M. Struch, Dr. P. Wandeler, B. Zimmermann and F. Bernhart. The game wardens M. Conti, P. Deleury, P. Matthieu and B. Reymond supported the fieldwork in many respects. M. Scholl was piloting the search flights and solved numerous technical problems. Dr. G. Neiger-Aeschbacher helped us to develop a protocol for a safe methetomidin-ketavet anaesthesia in the field. The study in Switzerland was funded by the Swiss Agency for Environment (Buwal), the head of the wildlife department Dr. H.J. Blankenhorn supported the project over all these years with great interest, by the Swiss League for Protection of Nature (Pro Natura), WWF Switzerland, the canton of Vaud, the Society for the Protection of Animals of the Canton of Vaud, the Agassiz foundation, and in the initial phase by the Swiss Foundation for the Scientific Research (project no. 3.119-0.-0.85, grant to U. Breitenmoser). We are grateful to the people who helped us in the field in France, in particular to the national gamekeepers (SD-ONCFS) from the Jura region for catching the lynx and fitting them with collars. L. Coat, Y. Coat, A. Garnier and S. Ruette have participated in collecting the telemetry data. We also thank DDAF-39 and FDC-39 for their support and P. Migot Head of Predators and depredators Unit (applied research department of the ONCFS). The French study was supported by the French Ministry of Environment, Nature and Landscapes Directorate.

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Christine Breitenmoser-Würsten, Fridolin Zimmermann, Anja Molinari-Jobin, Paolo Molinari, Simon Capt, Jean-Michel Vandel, Philippe Stahl, and Urs Breitenmoser "Spatial and Social stability of a Eurasian lynx Lynx lynx population: an assessment of 10 years of observation in the Jura Mountains," Wildlife Biology 13(4), 365-380, (1 December 2007). https://doi.org/10.2981/0909-6396(2007)13[365:SASSOA]2.0.CO;2
Received: 12 August 2004; Accepted: 3 April 2007; Published: 1 December 2007
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