Director, Skansen Zoo, Skansen Foundation

156

I n / Zoo Yh (1990) 2 9 156 163

Breeding the Wolverine

in Scandinavian zoos Gulo gulo

LEIF BLOMQVIST’ & HANS-OVE LARSSON’ ‘Zoologist, Helsinki Zoo, Korkeasuari, SF-00570 Helsinki, Finland und Assistant

, I S-115 21, Stockholm, Sicwkn

The Wolverine Gulo gulo is listed as Vulnerable in the wild (IUCN, 1988) and only small populations exist in captivity where breeding is limited. The authors have compiled data on captive breeding from 1915 to the present and keep an unofficial studbook for the species. In this paper we present breeding data on the Wolverine and introduce the measures now being taken in Scandinavian zoos for its protection.

DISTRIBUTION IN THE WILD The Wolverine is the largest of the land- living Mustelidae. The 25 weigh around 1 1 kg with 38 some 5 kg heavier, al- though some individuals may weigh up to 35 kg. Body length is about 100 cm and the height at the shoulder about 45cm (Krott, 1959). The glossy fur is dark brown, almost black on the back, legs, tail and parts of the belly; a lighter yellow- brown. sometimes almost white, band runs along both sides of the body from shoulder to rump and there is a pale patch on the underbelly. A pale mask around the eyes is usually more apparent in cubs and juveniles.

In relation to its body size the Wolver- ine’s paws are large (the fore paws of an adult 2 can measure 16 x 12 cm) and are covered with dense hair, which grows thicker in the winter giving the animal excellent support in the snow. Despite its clumsy appearance and its waddling gait i t can be a successful predator especially during the winter and early spring when snow supports the Wolverine but hampers

its prey, usually Reindeer Rang1fL.r turun- dus in Europe. Like many mustelids, the Wolverine often kills more than it can eat and this has given i t a bad reputation among the Reindeer herders in Lapland. Surplus killing and actual storing of food are known to occur, particularly among If”;’ with cubs and food storage has been observed in zoo animals when an over- abundance of food has been provided. In general the Wolverine has a varied diet. consisting mainly of small rodents and birds but it also eats carcasses and prob- ably obtains a substantial part of its diet by scavaging, following the tracks of other predators. such as Wolves Cani.7 lupus and Lynx Lj>ns 1 ~ ~ s . Like the Brown bear Ursus arctos, it feeds on berries when they are available.

The Wolverine’s distribution is circum- polar from Norway in the west. across the Fennoscandian penninsula, the USSR. Mongolia and China and throughout Alaska and Canada with isolated popula- tions in the USA as far south as central California (Fig. 1). Its home range is mainly restricted to the taiga in Eurasia and North America but in Scandinavia, i t also lives north of the boreal zone, mainly because interference from man has forced the animals to withdraw to the tundra. In the southern parts of its range. as in southern Norway, the Wolverine occurs only in the mountains. In California it has never been seen at a lower altitude than 400 m (Schempf & White, 1977).

In view of its wide distribution. i t is not surprising that three subspecies have been

I57

L

Fig. 1. The distribution of the Wolterine G i h gu/o is circumpolar, mainly restricted to tht boreal zones of Eurasia and North America.

distinguished in Eurasia (Heptner (’I ul.. 1974). From west to east. they arc G. g. g h . G. g. ,sibiricirs and G. g. ulhus. with lighter coloured individuals becoming more common towards the east. The Kamchatka subspecies G. g. rilhirs is relatively well defined. The four north American subspecies. G. g . I i r c u s . G. g . kutc.lititnrikrti.sis, G. 8. 1 u r n r . v and G. g . ~ti t i~,ou~ler~ti .si .s are separate by craniological characteristics from the Eurasian populations.

DISTRIBUTION IN SCANDINAVIA The species is listed in Annex I 1 of the Berne Convention requiring that contracting parties pay special attention to i t . Its present distribution in Scanda- navia is shown in Fig. 2.

Fitilund The Wolverine is found mainly in the north-eastern parts of Finland. where i t is in close contact with animals on the Soviet side of the border and the size of the population depends on the prey available. In addition to Lapland and the eastern part of Karelia. young animals are found in more southern parts of Finland. With an estimated population of only 33 animals in the border regions in January

1988. i t is one of Finland’s most endan- gered species. A further five to ten animals are believed to live in inland areas (Pulliainen. 1988). Although the species is protected. special hunting licences are granted. even though losses from Rein- deer herds are compensated for by the state.

Fig. 2. Distribution of the Wolterine in Scandinatia: a. areas of main distribution: b.arcus of possible occurrence.

Su.eden The main population exists in the high mountain regions in the Swedish parts of Lapland, but some animals are found in parts of Jamtland. Although often found on the barren tundra in high mountains. the Wolverine takes about 90% of its prey in nearby forests. Extra- polating from a survey made in 1972, it was estimated that in 1975 some 75 animals lived in Sweden. In 1988 there were indications of a stable population of about 120 animals and this has probably been the case for the last ten to 15 years. The sex and age composition of the popu-

lation is largely unknown. The species is protected in Sweden but if predation of Reindeer herds is substantial, the herders in Lapland are given licences to kill a specified number.

Norway The Wolverine has spread widely into the northern mountain regions and isolated populations also exist in the southern mountains. Norway has the largest population of Wolverines in Scan- dinavia and the numbers seem to have been stable since 1970. In 1978 1983 the minimum population was estimated as

DATE OF MATING

DATE OF BIRTH -~

6 Mar 1915 27 Feb 1916 17 Feh 1917 17 Feb 1917 20 Feb 1944 17 Feb 1945

Copen hagen

Stockholm 17-22 Jul 1916 17-22 Jul 1916

3 7

4 23-25 Mar 1944 30 Mar 1945 2 6 3 0 May 1954 18 Apr 1956

Hoes

Bor i s

12 Feb 1975 20 Feb 1980 22 Mar 1970 12 Mar 1973

I .o 0. I 0 . 2 I . !

1 .o 0. I

1.1 29 May 1973

19-31 May 1984 11-14 Jul 1985 29-31 May 1986

2-3 Jul 1981

73 Feb 1981 0 I 0. 1

8 Mar 1987 Feb 1982 22 Feb 1984 25 Feb 1985 13 Feb 1986

28 Feb 1988 19 Feh 1983

0.2 0 2 1 . 1 I .o 2.0

I .u 1 . 1

Ahtiiri

R m u n

Helsinki

30 Jun-2 Jul 1985 29-31 Jun 1987 10-11 Jun 1982 25-26 May 1983 23-24 Jun 1986 10-17 Jun 1987 1G11 Jun 1988

2 Mar 1987 29 Feb 1988 15 Feb 1989 March 1979 16 Feb 1965 1978 1980 26 Feb 1973

7 Mar 1985

i .3 0 .3 1 .o 1 .2 7

1 . 1 0 3

N o vos i hi rs k I Colorado Springs’

0. I I .o 2 1 1 2

Bisniasc k ,’ Winnipeg

31 May 1972 I . ?

9.14.10 1 5 2 7 I6

‘Shilo & Tamdrovskaya. 1981, LDavies, 1967, 3Mehrer. 1976 Table I . Births of the Wolverine Gulo pulo reported in zoos in the years 19151989.

N t W 01 V k L O P M C N T C lh ril l /OO W O K 1 I)

2 0

15

1 0 .

5 -

I59

- -

118-183 animals (Kvam ('1 id., 1988). Six distinct populations have been defined. the largest containing some 70 animals.

KEPKODUCTION Very little is known about reproduction in the Wolverine. The species is seldom kept in captivity and on 30 June 1988 only 9.10 individuals were registered with ISIS. Excluding Helsinki Zoo. which is one of the four zoos in Scandinavia which participates in ISIS, there are 12.8 Wolverines in zoos in the region. In addi- tion. there are 7.4 Wolverines in four Soviet zoos. We have collected data on 9.14.10 successful births during the last 75 years. 1915 1989. which occurred in 1 1 zoos. seven of them in Denmark. Sweden and Finland (Table I ) .

Like several other species of the Muste- lidae, the Wolverine is reported to have a delayed implantation, with mating taking place in the summer and the carrying the fertilized eggs until the following winter. Once implantation takes place, the foetuses develop quickly and the cubs are born after 3 W O days in early winter (Rausch & Pearson. 1972: Pulliainen. 1983; Banci & Harestad. 1988).

The birth season has long been known from the wild but because mating has seldom been observed a number of different assumptions have been made on the timing of the mating season. Pulliainen (1968) referred to the Russian studies where Ognev (1962) stated that oestrus occurs in January to February. Parovchcikov (1960) reported that the species mated in late July to early September in the Archangel. whereas Makridin (1964) mentioned that it might be possible that the mating season occurs after parturition in late winter concurring with Ognev's assumptions. In American literature also there are scattered state- ments which indicate that mating takes place in March and the cubs are born in June (Wright & Rausch. 1955). Wright and Rausch studied the reproductive tracts of 2 2 . I I Wolverines taken in Alaska and concluded that the species has a long

15 I 3

21 38 I3 32 1 2

,- > I

1 6

238 ~ ~~ ~

Table 2. Litter sizes of the Wolverine recorded in the wild.

occurred between 13 February to 22 March (Fig. 3) also agreeing with data from the wild. Pulliainen, based on data from 3 1 Wolverine breeding dens in north Finland, states that parturition occurs in January to March. These dates are confirmed for breeding VS; in Sweden (Krott, 1959; Haglund, 1959); Myrberget (1967) reported that dens were found between March to May in Norway. Parovchcikov (1960) reported dens with cubs during February to May in the Soviet Union. The timing of parturition during an apparently inhospitable period, coincides with the Wolverine's improved food supply during winter. Not only is the Wolverine a most successful predator in snow but also many Reindeer starve to death in hard weather and carrion is plentiful.

In observations made on a total of 248 Wolverine dens in the wild, the mean litter size was 2.4 (Table 2). In zoos the data we have collected give a mean of 2.1 but cub mortality in the wild is likely to be high. Pulliainen reports a captured carrying five foetuses. Because most of the captive breeding animals have been kept in large enclosures where the 7 has dug her own den making it difficult or impossible to check on newborn cubs. it is possible that the litter size may be higher than recorded. Of the total of 54 cubs bred in captivity 70% have been sexed, giving a

ratio of 1 : 1 5 ($:<). Based on the limited data available from zoos. at birth the cubs weigh c. 90g (12 = 6) (Table3) but the growth rate is rapid. By one-and-a-half months, the mean of four ;;. of known weight was over 15 times heavier than the birth mean for ;< and the only 3 weighed at this age was more than 23 times heavier than the mean of three -3 birth weights. (Unfortunately none of the individuals was weighed at birth and at a later date to give a direct comparison; obtaining the birth weight of mother-reared cubs will probably always be impractical.) In May when the cubs leave the den in the wild. they weigh 445 kg.

The cubs are born blind but covered with a light cream pelage which they begin to moult at the age of three-and-a-half months. In the wild in the taiga region the den made by the dam begins to melt in April or May forcing the cubs to leave. Captive-bred cubs are seen to investigate their enclosures about this time and by six to seven months they are almost indepen- dent of the mother, although in the wild they continue to follow her throughout the autumn. They grow to sexual maturity at the age of three to four years. In our records the youngest ,t to have given birth was a three-year-old at Helsinki Zoo while the youngest 3 to sire cubs was four years old.

In June 1988 of the 20 Wolverines

. .

R I H T H .wit (mon ths ) -

? '. F 3 3.5 3 5 I 1.5 - . -

93. I 104 x4

8 50 x75 w

400 3 50 520 550

M t A N 94 x75 I355 X5.6 X3.5 X- l

.. I )

'OOO M t A N 84.7

2000 2ooo 1950

7400 74(Hl 7173

2290

3000

7600

Table 3. Weights (in grams) of captive-bred Wolverine cubs. Data are taken from Swosibirsk Zoo (Shilo & Tamarovskaya. 1981). Dakota Zoo. Bismarck (Mehrer. 1976). f'ulliainen (1974) and Htlsinki Zoo records.

recorded in zoos in North America. 19 were of known age. a mean of 6.8 years (range 0 16 years). The corresponding mean for the captive population in Scan- dinavia is 4.6 years. The mean longevity of live wild-caught animals kept at Helsinki Zoo in the early 1970s to 1980s was I 1.2 years ( 10 13 years). The maxi- mum longevity recorded was 17 years 4 months for a G . g. Itrsc.u.s (Jones. 1979).

CAPTIVE MANAGEMENT The Wolverine is a solitary animal although in captivity they are usually kept as a pair. Some 100s keep several animals in the same enclosure and havc succeedcd in breeding under these conditions but i t is not recommended. In such cases the group has often been built up from a breeding pair plus its offspring or with young animals which have been kept together since they were cubs. I f the pair is housed separately, they should be put together in early May as the breeding season is confined almost exclusively to May and June. At the end of the year. the : should be separated from her matc and preferably given free access to a nestbox.

In Sweden regulations for keeping the species require a minimum enclosure o f

800mL. furnished with logs. stones and a substrate in which the animals can dig. As the Wolverine is a superb climber. i t necessary to prevent i t from climbing trees near to the perimeter fence by electric fences or collars of surong. climb-proof material around the trunks. Since the animals are capable of climbing up wire- mesh. this cannot be used for enclosure walls unless protected by electric fcnces or lined with smooth plastic sheets. The walls of most existing enclosures are concrete and need to be at least 2 m high since an adult can jump to a height of 1.5m and even an I I week-old cub has been reported as jumping to a height o f I m (Krott. 1059).

The pregnant . needs to be separated in late December into a smaller enclosure with access to a nestbax. We recommend a nestbox. measuring 70 x 50 x 70 cm high. with one entrance and an inspection door in [he roof protected by strong wire- mesh. Nesting material. such as hay o r straw. should be supplicd. Like most mustelids. Wolverines are highly nervous during parturition and thc dam will kill her offspring if disturbed. The breeding enclosure therefore should be o u t of sight and totally secure from disturbance by the

I02

public. In zoos where the has not been separated and provided with a nestbox she has dug a den which has prevented the keepers from checking on the cubs.

As a general rule, it cannot be recom- mended that zoo staff enter an enclosure with Wolverines and for successful mana- gement each breeding unit requires three separate enclosures, the main living area for display and two holding enclosures for use during cleaning of the main exhibit or as a birthing den.

SCANDINAVIAN BREEDING PROGRAMME The Wolverine has always played a special role in Scandinavian zoos, many of which exhibit only native fauna. During the last few years the Wolverine stock has been surveyed and several transfers between Swedish and Finnish zoos have taken place in order to establish breeding pairs. An unofficial Scandina- vian studbook for the species has been kept by the authors. At a Scandinavian zoo congress in Ranua Zoo, Finland, in 1987. it was agreed that the Wolverine be given a high priority. As several zoos have received enquiries from other European zoos and some animal dealers, it was agreed that no animals should be sold outside Scandinavia as long as there was a demand among Scandinavian zoos. First a healthy breeding stock needs to be established to achieve a self-sustaining captive population. Because of the situa- tion in the wild, the immediate aim is to build up the zoo population and even- tually we would want to reintroduce the species to areas from which it has disap- peared. However, until circumstances change, this is not a realistic enterprise, especially in Lapland where the Wolverine is regarded as a severe threat to the domestic Reindeer. Once the situation with the captive population is satisfac- tory, there is no reason to prohibit the export of captive-bred specimens to other zoos interested in breeding the species. At time of writing there are 8.6 animals located in six Swedish zoos and 7.6 animals in three Finnish zoos. A new

age class 10-11

9-10 8 - 9 7 - 0 6 - 7 5 - 6 4 - 5 3 - 4 2 -3

1 2 3 4 5 n o . of a n i m a l s

Fig. 5. Age distribution of 27(15.12) Woherines in Scandinavian zoos in 1988. The mean age of the population was 4.6 years.

breeding centre for endangered species. The Nordic Ark, has recently been opened on the west coast of Sweden and will include at least two pairs of Wolver- ines in its breeding programme. Also. there are two zoos in Sweden. Froso Zoo and Eskilstuna's Parken Zoo, which do not yet keep the species. I t is hoped that they will soon also be able to include the Wolverine in their collections. At present there are no Wolverines in zoos in Norway or Denmark.

The age distribution of the captive stock in Scandinavia varies from 0- 10 years with an average of 4.6 years (Fig. 5). As sexual maturity is reached by the age of three to four years. this is favourable for future breeding. The nine (8.1) wild- caught animals in the present population are five to ten years old. Only four of the Jj' have bred (three of which are in Finland and one in Sweden) leaving the other 4.1 animals as potential founders. The remaining 18 (7.1 1) animals are captive-bred. It is of the greatest impor- tance that the remaining wild-born speci- mens are included in the breeding population to give a broader genetic base. A 2 and G which had been kept together as a pair at Lycksele Zoo without repro- ducing have now been separated and introduced to new partners in the hope of inducing them to bred. The behaviour of two other potential sires in Stockholm and Kolmarden looks promising for the future.

I63

4C'hhOWLt.MikMt.h I S

We wish to extend ou r thanks to the following who kindly supplied us with inforniation concerning the captivc population: N . Hilldcn. Borasparken. M. hmmundin. Kolniardens Djurpark. F.. Pykili inen. Ranua Zoo and J . Lahtinen. Ah t i r i Zoo.

REFERENCES BAN(.I. V. a I ~ A R ~ S ' I A U . A. (1988): Reproduction and natality o f wolverine I Gu/o g i r k i 1 in Yukon. :inn. Zocrl. Fev/t/. 25: 265-270. DAVIFS. 1). G. (1967): A hrief note on the hirth o f wolverines Gulo K u / o at Colorado Zoo. / f i r . Zoo 1.h. 7: 127. HAGLI:?;~). H (1969): Di, f i r u vroru. Stockholm: Pan Norstcdts. ~ I E P T Y F R . V. G . . NAIMW. N. P.. J I :R< SLLIIXKI. A. A, . C I K K ~ V A . A. I... & BANNIK~V. A. G . (1974): Gat tung Girlo Storr 1780. Vielfrasse. In Dit Sijugcricw cfcr Sowjc'runiriii 2: 6(W-623. Jena: VEB Gustav Fischer Vcrlag. IUCN ( 1988): 19XX Il'CN rcd /is/ t i / ' rhrsuwncd uninials. Gland. Cambridge: 1lJCN. JONES. M. L. (1979): Longevity of mammals in captivity. I n / . Zoo N c ~ 26(3): 16 26. KKOTT. P. (1959): Dcr Viell'rass f G u l o p l o L 17%). Mono.qruphiiw dcr U'ild Saugc'ritw No. 13. Jena: VEB Gustav Fischcr Vcrlag. K V A M . T.. 0 v ~ ~ ~ ~ t n i . c ; . K . & &jW)RI:N (1988): The wolverine Gido pu/o in Norway. Lurru 31: 7 20.

behavior of free-ranging wolverines / Gu/o , q u / o ~ . Acru :oo/. Icnn. No. 174: 175-177. MAKRIDIN. V. P. (1964): The distribution biology of the wolverine. Zoo. Zhurn. 43 1688-1692. (In Russian.] M w u R . C . F. (1976): Gestation period in the wolverine G i h g u h . J. Muniniul. 57: 570. MYHRK. R . (unpubl.): Jc,rvc*ii i Nor,qc.- A/[fc,r.ro,ic//~..F[,, rc~proifuk.sjon ox c'riuwruig. llniversity of Oslo. 1968. (In Norwcgian.] MYRRI(RG1iT. S. (1967): D c tire store rovdyrene i

Norge. ,Vu/urcn 91: 228- 240.

MACOIIN. A. J . a VALKtNHI'R(i. P. (19x3): Breeding

M \ K H ~ K G L I . S. a SOHUMGARI). R. (1979): Time of hirth and littcr si7c in wolvcrinch. F~rirnu 32: 9 I ? . Iln Norwcgian. J NASIMOVICH. A. A . (1948). Neue Dawn m r Oliologic dcs Viclfrasws in1 Lapplindischcn Naturschutzgchici. .Arbe,mti L/C.S .%IIII. 1.upp- /iInl//.wh~v~ N c r r i t r , s ~ ~ / i u r ~ . q c ~ t ~ i ~ ~ r ~ . r 3: I97 124. OGSEV. S. I . (1962): .4fun/mul.r of 1;SSR uni/ui&mw/ coutitricT 3. Curnrwru. Jcrus4lem: Israel Program for Scientific Translation. (Translated from the Russian.] PAROVCHCIKOV, W . J . t 1960). Biolog! o f thc wol\'crine. t o o l . Zhurn. 2 9 I I I I . [In Russian.] I? .LLIAINFS. E. ( 1968): Brceding biology o f the wolverine (Girlo , q i h L.) in Finland. .Ann. ZOO/. Fcwn. 5: 338-344 PULI IAISES. E. (1972). Ahniu. In Siromcn Nuiikkdiir 2: 245- 264. Siivonen. L. (Ed.) . Otava: Helsinki. PULLIAINEN. E. (1974): Ahniu. In Suomew suurpcdor; 161 -193. Helsinki: Tammi. PIILLIAISFN. E. (1983): Ahnw. In Suonicw diiinicr I: 240 244. Koivistn. I . (Ed . ) . Helsinki: Weilin & Giiiis. PLII.LIAISFV. E. ( 19x8): Ecology. status and managcmcnt of the Finnish wolvenne G d o K i h

populations. /.irrro 31: 21 -28 , RALWH. R. A . & PEARSON. A. M. (1972): Notes on the wolverine in Alaska and the Yukon territory. J. Wild/. M,qnr/ 36: '49 26X. S C . H E M P t . 1'. & WHiI.1.. M. (1977): .%lu/ir.r of .ri.\ furhrurrr p ( ~ p ~ / ~ I i ~ i i . \ I n the, niounrums of riorrhcrn Culrforniu. US Department of Agriculture Forestry Service. California Region.

growth and development of wolverines Gulo Kulo at Novosibirsk Zoo. In!. A i o t b . 21: 1 4 6 1 4 7 . SIIVONTN. L. ( 1956): Suuri nrsuku,skir/u. Helsinki; Mammalia Fennica. Iln Finnish.] WRIGHT. P. L. & RAI:X'H. R. (1955): Reproduction in the wolverine G'uh ~ u l t ~ . J. .Uunimu/. -16: 346 355. 7 r m R R E R c ; . H . ( 1 9 4 9 : Tva frcdliisa. Uppsala. [In Swedish.]

SIIILO. R. A . B . rAMAROVSKf lYA\ . M . A . (19x1): The

Manuscript submitted 20 September 1989