The wolverine exhibits a polygamous mating system where one male usually mates with several females (Hedmark et al. 2007). Wolverines have an extended mating period and are believed to mate from May to August (Wright and Rausch 1955, Rausch and Pearson 1972). Most matings probably occur in June-July (Mead et al. 1991, Pasitschniak-Arts and Larivière 1995, Blomqvist 2001).
Wolverines exhibit delayed implantation. Fertilized eggs develop to the 8-cell stage (blastocyst), then remain in this stage until implantation into the uterine wall, usually occurring from December to February (Banci and Harestad 1988). Post-implantation following implantation of the blastocyst is about 30-50 days (Mead et al. 1993, Rausch and Pearson 1972, Pasitschniak-Arts and Larivière 1995).
Parturition occurs from January through April, with most females giving birth in February to mid-March (Rausch and Pearson 1972, Banci and Harestad 1988, Magoun and Copeland 1998). Young are born fully furred with eyes closed and teeth not erupted. At birth their fur is white, they weigh an average of 84.0 grams, and have a crown-rump length of 121.0 mm (Davis 1967). Young are weaned at 9-10 weeks (Iversen 1972) and begin to travel with mothers in early summer. Juvenile wolverines are nearly full-grown and probably nutritionally independent from the mother by September (May et al. 2008). Males appear to reach sexual maturity at about 2 years of age (Banci 1987). Female wolverines attain sexual maturity at about 15 months (Banci 1987), but research has shown that it is very rare that 2-year-old females produce litters that survive long enough to be detected in the field (Persson et al. 2006). In general, wolverine females have a low reproductive rate. Although pregnancy rates determined from reproductive tracts of harvested wolverines (Banci 1994) suggest that most adult females mate every year, the proportion of females that successfully rear young appears to be low. In a large-scale study of wolverine reproduction in Scandinavia, the proportion of females (> 2 years old) that reproduced each year was only 53%, and the number of offspring per female in May/June was 0.74 (Persson et al. 2006). Litter size is on average about 1.8-2.0 (Magoun 1985, Copeland 1996, Persson et al. 2006). Reasons for the low reproductive rate are that reproduction incurs costs on female wolverines that affect future reproduction, and that reproduction is limited by winter food availability (Persson 2005). Presumably, female wolverine reproduction is determined by their condition in winter, which is a result of the combined effect of reproductive costs and winter food availability.
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Banci, V. and A. S. Harestad. 1988. Reproduction and natality of wolverine Gulo gulo in Yukon. Annales Zoologici Fennici 25: 265–270.
Banci, V. 1987. Ecology and behaviour of wolverine in Yukon. M.Sc. thesis. Simon Fraser University, Burnaby, Canada.
Banci, V. 1994. Wolverine. In: Ruggiero, L.F., K.K. Aubry, S.W. Buskirk, L.J. Lyonand W.J. Zielinski (eds). The scientific basis for conserving forest carnivores. American marten, fisher, lynx and wolverine in the western United States. U.S. Forest Service General Technical Report RM-254. Fort Collins, Colorado, USA. Pp. 99-123.
Blomqvist, L. 2001. Management of captive wolverines Gulo gulo in Europe: Studbook and guidelines to husbandry, vol 2. European Association of Zoos and Aquaria. Vimmerby, Sweden.
Copeland, J.P. 1996. Biology of the wolverine in central Idaho. M.Sc. thesis, University of Idaho, Moscow, USA.
Davis, D. G. 1967. A brief note on the birth of wolverines Gulo gulo at Colorado Zoo. International Zoo Yearbook: 7:127.
Hedmark E., J. Persson, P. Segerström, A. Landa and H. Ellegren. 2007. Paternity and mating system in wolverines Gulo gulo. Wildlife Biology 13(Suppl 2):13–30.
Mead, R.A., M. Rector, G. Starypan, S. Neirinckx, M. Jones, and M.N. Don Carlos. 1991. Reproductive biology of captive wolverines. Journal of Mammalogy 72, 807–814.
Mead, R. A., M. Bowles, G. Starypan, and M. Jones. 1993. Evidence for pseudopregnancy and induced ovulation in captive wolverines (Gulo gulo). Zoo Biology 12:353–358.
Magoun, A.J. 1985. Population characteristics, ecology and management of wolverines in northwestern Alaska. Ph.D. dissertation, University of Alaska, Fairbanks, USA.
Magoun, A. J. and J. P. Copeland. 1998. Characteristics of wolverine reproductive den sites. Journal of Wildlife Management 62:1313–1320.
Iversen, J.A. 1972. Metabolic rate of wolverines during growth. Norwegian Journal of Zoology 20:317–322.
May, R., J. van Dijk, R. Andersen and A. Landa. 2008. Wolverines in a changing world – Final report of the Norwegian wolverine project 2003-2007. NINA Report 434.
Pasitschniak-Arts, M., and S. Lariviere. 1995. Gulo gulo. Mamm. Species, 499: 1–10.
Persson J, A. Landa, R. Andersen, and P. Segerström. 2006. Reproductive characteristics of female wolverines (Gulo gulo) in Scandinavia. Journal of Mammalogy 87:75–79.
Persson, J. 2005. Female wolverine reproduction: reproductive costs and winter food availability. Canadian Journal of Zoology 83:1453–1459.
Rausch, R.A. and A.M. Pearson 1972. Notes on the wolverine in Alaska and the Yukon Territory. Journal of Wildlife Management 36:249–268.
Wright, P. L. and R.A. Rausch. 1955. Reproduction in the wolverine, (Gulo gulo). Journal of Mammalogy. 36:346-355.