Wolverine (Gulo gulo)

Barents sea region red-listed species
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The Wolverine is a powerful northern carnivore which is well adapted to long and cold winters. It is the largest species in the weasel family (Mustelidae). The length of the wolverine is 70–80 cm. Males weigh usually 12–18 kg, females are 8–13 kg. The legs are short, the head is broad the eyes are small, and the ears are short and rounded. The fur is dark somrtimes pale on the sides brown and thick. The wolverines are nocturnal, opportunistic predators, which 

live solitarily most of the year and communicate with each other trough scent marking and short-range vocalizations.

Distribution/range – global and regional

The wolverine is distributed in central and northern parts of Norway, Sweden, Finland and northwestern Russia excluding the northernmost tundra regions (Landa et al. 2000, Abramov et al. 2009). In Scandinavia the core area includes mountainous regions of northern Norway and Sweden, In Finland North Lapland with more fragmented distribution in easternmost part of the country. More scattered wolverines live also in some regions further south in all three Nordic countries. In Russia wolverines are distributed along the taiga zone, as well as in North America. Up to the 1800s the range extended south of the Baltic Sea.

Key habitats - seasonality

Wolverines have adapted to live in a broad scale of habitats from boreal coniferous forests to alpine habitats, if suitable food, shelter and safe den sites in remote valleys with steep slopes are available (Landa et al. 2000, Abramov et al. 2009). Wolverines prefer areas where snow lasts late in spring both for reproduction, preying and caching food (Copeland et al. 2010, Inman et al. 2012). Most wolverines live in remote and extensive upland habitats with alpine heath, birch forest and barren coniferous forests. After population recovery, especially in some southern parts of the range, the wolverines have been able to invade areas closer to roads, dispersed settlements, recreational activities and other human influence if there is suitable wild prey available, and den sites remain undisturbed. The species lived also in temperate deciduous forests before deforestation, human expansion and persecution pushed the range northwards and upwards.

Biology – migration, life strategy, feeding, trophic relation, etc.

Wolverines live solitarily most of the year. Females with cubs wander usually within the smallest home ranges, varying from 40 to 100 km2, while the home range of males and females without cubs is much larger, typically from 200 to 1.500 km2 (Landa et al. 2000). Wolverines are polygamous (Hedmark et al. 2007). The male and female mate from April to August and fertilized eggs remain as blastocysts up to implantation from November to March. Most females give birth from January to late March. Litter size is 1–5, on the average 2–3. Female wolverines become sexually mature at the age of 15 months, but all individuals do not produce cubs every year (Persson et al. 2006). Wolverines die typically at the age of 4–6 years, but at least 13 years old individuals have been recorded (Abramov et al. 2009). Especially in winter wolverines obtain most food as scavengers utilizing carcasses of large mammals left by other carnivores like wolves and lynxes, and animals died from disease or accidents. Wolverines are able to prey on reindeer throughout year and domestic sheep when grazing in upland pastures in summertime. They hunt regularly smaller prey, too, such as mountain hares (Lepus timidus), Ptarmigan (Lagopus spp.) and small rodents, which may form a marked part of the summer diet. In parts of the range with few large carnivores and a reduced supply of carrion, like in central Norway, the average litter size is dependent on vole densities. If there is plenty of food available wolverines cache excess part of it for later use.

Population status – numbers and trends

There exists no current estimate for the North American population but it must be some tens of thousands of animals, as the density varies from 0.3 to 15 animals/1.000 km2 (Abramov et al. 2009). In eastern Russia, east of the Ural Mountains, there are over 18.000 animals. The European population is at present well over 2.000 wolverines (Abramov et al. 2009). In Norway there are 336 (284-427), in Sweden 585 (481—758), in Finland 230–250 individuals. In European Russia the population was estimated at 1.400 wolverines a decade ago (Abramov et al. 2009), of which perhaps ca. 100 live in Kola Peninsula, less than 100 in Karelia, ca. 400 in Archangels Oblast, and ca. 800 in Komi, respectively (Landa et al. 2000). Wolverine populations have recovered slowly and extended their range to coniferous forests and pine peat bogs further south in South Norway, Central Sweden and East Finland since the late 20th century. In opposite to Scandinavia and Finland, the Russian population has reported to be declined during the last 50 years. The connection and gene flow between the common wolverine population in Finland, Kola and Karelia and that further east in Russia is poorly documented and dependent on the influx of individuals through the fairly narrow taiga corridor between the White Sea and the Lake Onega. The global population of the wolverine is decreasing (Abramov et al. 2009).

Threats – natural and anthropogenic

The major problems for the long-term and viable existense of the wolverine in the Barents region are small population size, fragmented distributions, and presumed low genetic diversity (Landa et al. 2000). Regional populations may not become completely genetically mixed, in spite of the fact that individual wolverines make long-distance movements. Stochastic events may have a drastic influence on sex and age distribution and viability of such a small population in spite of fairly wide distribution, connected to the slow reproductive rate. The main reason for the unnaturally low density of the Fenno-Scandian population, however, is too heavy killing rate both legally and illegally, motivated by depredation of livestock by wolverines (Landa et al. 2000, Abramov et al. 2009, Hobbs et al. 2012). Wolverines kill semi-domestic reindeer throughout the year in all three Nordic countries, and, in addition, unattended sheep in Norway during summer. Hundreds of wolverines have been shot as depredation control, including poaching, since the species became legally protected a few decades ago in all Nordic countries. In Russia, wolverine is a hunted species, but the illegal killing rate is high as shown by declining population trend. Optimal habitat has also been lost and degraded due to various kinds of human activity, which affect both directly (road and settlement construction, disturbance by recreational activity) and indirectly (decline in other carnivore populations providing carcasses). Intensive grazing by huge numbers of sheep and reindeer may alter living conditions of small vertebrates preyed by wolverines. Climate change will degrade living conditions of the wolverine drastically because both preying and reproduction are highly dependent on optimal snow conditions.

Conservation measures and needs

Wolverines are protected by the Bern Convention (1979) and the UNCED Convetion (Rio de Janeiro 1992) in Scandinavia and Finland, and additionally by EU Habitats Directive (1992) in Sweden and Finland. The species is classified as threatened in the Nordic countries (Norway endangered, Sweden vulnerable, Finland critically endangered). The major problem in wolverine conservation is the conflict with livestock husbandry. More intensive measures should be put into force against poaching. Wolverine habitats and den sites should be protected and further fragmentation prohibited by preventing recreational developments, and taking wolverine and its prey more carefully into account when planning roads, hydropower dams etc. Further research should be especially concentrated on population dynamics, dispersal, habitat use, and more reliable monitoring methods.