The Swedish wolverine project
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ecology and conservation

Project leader:
Jens Persson
Department of Animal Ecology
Swedish University of Agricultural Sciences
SE-901 83
Umeå, Sweden
E-mail: jens.persson@szooek.slu.se

Field technicians:
Peter Segerström
Tom Wiklund

Project summary [Click photos to supersize]

The Swedish wolverine project is an ongoing study initiated in 1993. The overall aim of this project is to gain information on the population dynamics of the Scandinavian wolverine, in order to facilitate science-based management and conservation of the species in Sweden.

The Swedish wolverine population is sympatric with reindeer and distributed along the mountain range in the north-western part of the country. The wolverine is legally protected in Sweden. The population was estimated at 326 ± 45 individuals during 1998-2000. The main prey of Swedish wolverines is reindeer. As a consequence, the main conservation problem is the conflict between wolverine and reindeer husbandry, leading to illegal killing of wolverines.

The study is based on data from individually radio-marked wolverines. A total of 168 wolverines have been captured and equipped with intraperitoneally implanted radio transmitters. Juveniles are captured by hand and equipped with transmitters mainly in late April to early June. Adult wolverines are darted from the ground or from helicopter. At capture, we take morphological measurements, retrieve a tooth for aging, sample tissue and hair for genetic analyses, and blood for veterinary medicinal analysis.

We determine positions for home range and dispersal analyses through bi-weekly radio-tracking from fixed-wing aircraft or from the ground. Reproduction of radio-marked wolverines is determined during the denning season by intensive radio-tracking of females greater than 24 months of age as well as visits on the ground to investigate the site of a suspected den in search of typical characteristics of a den site. Presence of kits and litter size is determined from early May to early June.

The study is conducted in and around Sarek National Park in Norrbotten County, northern Sweden. The area is characterised by deep valleys, glaciers and high plateaus with peaks ranging up to 2,000 m.a.s.l. The valleys are dominated by mountain birch (Betula pubescens), Scots pine (Pinus sylvestris), and Norway spruce (Picea abies). The study area is approximately 6,000 km² and the approximate density of wolverines is 1.4/100 km².

Results
None of the known-aged females (n=10) have reproduced before the age of 3 years, and the average age at first reproduction was at least 3.4 years. The proportion of adult females (37 females during 88 individual reproductive seasons) which reproduced each year was 0.54 and the average annual birth rate was 0.8 kits per female. The average size of 50 litters in mid May to early June was 1.9 and ranged from 1 to 3 kits.

We have found that reproduction incurs costs on females that affect reproduction the subsequent year. Experimental food-supplementation of females in early winter enhanced reproductive rates, even though all food-supplemented females had reproduced the preceding year. This suggests that reproductive success of wolverine females is determined by the combined effect of reproductive costs and winter food availability.

The survival rate of radio-marked juveniles from May to February was 68%. Intraspecific predation was the most important cause of juvenile mortality, and occurred in May-June when juveniles are dependent on their mother as well as in August-September after independence. The most important cause of adult mortality was illegal killing. Other causes of adult mortality were legal killing, avalanche and intraspecific predation.

The average dispersal age was 13 months for both males and females. All males and two-thirds of the females have dispersed. All sedentary females occupied their mother's territory when she died or shifted territory. Preliminary analyses indicate that adult females are strongly territorial.

In a population viability analysis we have shown that the Scandinavian wolverine population is strongly influenced by stochastic components. This includes first, a large demographic variance due to a very variable success in recruitment of juveniles to the age of 1 year. Second, it includes a high environmental variance, presumably due to variations in food availability.

The project is funded by the Swedish Environmental Protection Agency, Norwegian Directorate for Nature Management, World Wide Fund for Nature (WWF) Sweden.

Recent publications:

Vangen, K.M., Persson, J., Landa, A., Andersen, R. & Segerström, P. 2001. Characteristics of dispersal in wolverines. Canadian Journal of Zoology 79: 1641-1649.
Abstract: http://pubs.nrc-cnrc.gc.ca/cgi-bin/rp/rp2_abst_e?cjz_z01-124_79_ns_nf_cjz9-01

Persson, J., Willebrand, T., Landa, A., Andersen, R. & Segerström, P. 2003. The role of intraspecific predation in the survival of juvenile wolverines. Wildlife Biology 9: 21-28.
Abstract: http://www.wildlifebiology.com/2003/persson_.html

Persson, J. 2003. Population ecology of Scandinavian wolverines. PhD-thesis, Swedish University of Agricultural Sciences, Umeå, Sweden.
Summary of the thesis: http://diss-epsilon.slu.se/archive/00000205/