Mustelids (Mustelidae)

by Victoria Hillman - TWP Research Director

Copyright © 2012 Victoria Hillman
The mustelid family consists of badgers, otters, mink, weasels, polecats and martens, all of which possess the key feature of anal glands that produce a thick, oily, powerful-smelling discharge called musk which is used to mark their territories and from which they get their name. Species within this family are tough, voracious and often opportunistic predators capable of taking on prey much larger than themselves in some cases, but despite this they remain one of the least studied mammal groups in Europe. Members of this family share a number of other characteristics which include the male being slightly larger than the female and in all but the martens, non-retractable claws.

The following Mustelid species are thought to inhabit the Eastern Carpathians and below is a short introduction to each species including description, reproduction, habitat, diet and threats that they currently face:-

The Pine Marten (Martes martes)

Copyright © 2012 Victoria Hillman
The pine marten is between 40-55cm in length with a 20-28cm bushy tail, weighing between 0.9kg and 2kg. They have a chestnut to dark-brown pelt with cream to yellow “bib” the pattern of which is unique to each individual. The pine as with as the other marten species have semi-retractable claws and fur on the soles of their feet, a characteristic that is unique to these members of the family and aids them in their semi-arboreal existence.

Pine martens have a lifespan of eight to ten years, reaching sexually maturity between one and three years. Martens are solitary and polygamous animals coming together in late summer to mate with one to five sparsely furred, deaf, blind kits being born around early spring, the kits are full weaned at two months and are able to kill prey at around three to four months, shortly after which they will leave the safety of their mother. Delayed implantation of the fertilised egg of between 165 and 210 days until conditions are thought to be optimal

Copyright © 2012 Victoria Hillman
Present throughout the Palaearctic, with some exceptions, this species inhabit deciduous, coniferous and mixed woodlands as well as scrub although their dens are most often in the hollows of trees, they are most active at dusk and during the night. They have a varied diet consisting of small mammals, birds, insects, bird eggs, honey and nuts and berries when they are abundant. Although pine marten populations are considered stable across their entire range, threats such as habitat fragmentation, unsustainable trapping and hunting and incidental poisoning are ever present and pose risks to smaller more isolated populations.

The Beech Marten (Martes foina)

The beech marten, also known as the stone marten and house marten, is between 40-50cm in length with a bushy tail of 20-30cm, weighing between 0.5kg and 2.5kg. They have a rich, chocolaty pelt with a distinctive white bib that is forked by a brown stripe from the bottom of the throat and is one of the distinguishing features from that of the pine marten whose bib is creamy yellow. As with the pine marten, the beech marten has semi-retractable claws and fur on the soles of their feet, a characteristic that is unique to these members of the family and aids them in their semi-arboreal existence.

Beech martens have a lifespan of approximately 10 years reaching sexually maturity between 15 and 27 months. They are solitary animals coming together to breed between June and August where the males will endeavour to mate with any females within their territory with mating usually taking place at night and often lasting up to an hour. Implantation of the fertilised embryos is delayed for up to eight months until the following spring, once implanted development takes approximately one month after which two to four young are born blind, deaf and hairless. The young are fully weaned at two months but will stay with their mother while she teaches them to hunt; they will be fully independent and start to disperse towards the end of the summer.

Beech martens are present throughout Europe, northwards to Denmark and southwards towards Italy from sea level up to 4000metres during the summer months. They typically inhabit rocky areas and deciduous forests making their dens in tree hollows, rocky crevices and abandoned burrows but can also be found near human dwellings and are known to cause damage to cars and raid chicken coops. As with other mustelids, beech martens are omnivorous predators with a varied diet of birds’ eggs, fruit, invertebrates and small mammals. As with pine martens, beech marten populations are considered stable across their whole range however they are still susceptible to habitat fragmentation, rabies in smaller populations and hunting for their fur. This said, beech marten populations in part of Europe are thought to be on the increase and it is thought that this success is larger due to their ability to adapt and live in close proximity to humans.

The Eurasian Badger (Meles meles)

The Eurasian badger is between 60-90cm in length with a 15-24cm tail and up to 30cm to the shoulder. They weigh between 7kg and 17kg depending on the season, during the summer they are typically a few kilograms lighter than in autumn with a maximum weight of 19.5kg recorded for a male or boar. Although they have a very good sense of smell, their vision is monochromatic and their hearing is no better than that of humans. The badger is a stocky, powerfully built animal which lacks the flexibility of martens, polecats, weasels and stoats. The fur along the back, sides and tail is silvery-grey, they have two black and three white bands that widen from the nose to the neck and merge with the fur on the back, the eyes and ears are situated within the black bands. They are one of the most studied members of the mustelid family found in the Carpathians.

The Eurasian badger has a lifespan of approximately six years in the wild but can live to 14 and unlike other members of the mustelid family live in family groups or clans of up to 15 individuals in setts that can be over 100 years old passed on from generation to generation. Sexual maturity is reached between 12 months and two years with males typically becoming sexually mature before females. Badgers are monogamous pairing for life although it is not unusual for the female or sow to mate with more than one male or boar with only the dominate female breeding; although she may suppress reproduction of subordinates they help with the grooming, protection and feeding of the cubs. Mating can take place throughout the year but generally peaks between February and May, lasts from 15 minutes up to an hour. Unless mating takes place in December where implantation is immediate, there is delayed implantation of anywhere from two to nine months. Following a gestation period of seven weeks, a litter of two to three cubs is born blind, deaf and covered in a silvery fur, weighing 75-132grams and measuring approximately 12cm in length. The eyes open at five days along with the appearance of dark hairs and pigmentation of the claws. The milk teeth erupt at around five weeks and although they start to venture from the sett at nine weeks, when they follow their mother on foraging expeditions learning what to and what not to eat, they are fully weaned until around three months.

The badger is abundant throughout Europe, preferring deciduous woodland close to open pastureland and clearings but can also be found in coniferous and mixed woodlands, scrub and suburban areas. Setts are usually located within woodlands near to a tree and are unmistakable with anywhere from 10 to 50 entrance holes. Badgers, along with brown bears are the least carnivorous members of the Carnivora order being adaptable, opportunistic omnivores with adults eating around 3.4% of their body weight a day. The diet consists of everything from berries and nuts, roots and tubers, amphibians, invertebrates, cereal foods to small mammals including hedgehogs, moles and rabbits. Populations of Eurasian badger are consider stable, however they face numerous threats including persecution, killing as bycatch during fox hunts, land-use changes resulting in fragmentation of habitat to which they are particularly sensitive, baiting and road collisions. Over 50% of young badgers die in their first year with cubs falling prey to larger predators such as wolves, lynx and raptors.

The Least Weasel (Mustela nivalis)

The least weasel is the smallest carnivore in the world with a body length between 11-26cm in length with a 1.2-6cm tail, weighing between 30g and 250g. The body is thin, slender and incredibly flexible and the head is small with large, dark coloured eyes. The soles of the feet are covered with dense hair. The fur on the upper parts of the body ranges from dark chocolate to light tawny dependant on the habitat, whereas the fur on the underside from the lower jaw to the tail including the inside of the legs is white. During the winter the fur on the entire body turns white.

The least weasel has a lifespan of around two years in the wild reaching sexual maturity between three and four months. Mating takes place between April and July and following a 34-37 day gestation period the kits are born blind, deaf, pink and naked weighing between 1.5g and 4.5g. By the age of ten days the margin between the dark and lighter fur is visible, first teeth start emerging at around two to three weeks when they are weaned, by three to four weeks the eyes and ears are open and by eight weeks the killing behaviour has developed. Dispersal form the mother normally takes place at around 12 weeks.

The least weasel has a circumboreal (largest floristic region in the world), Holarctic distribution inhabiting forests, farmland, meadows, scrub, hedgerows and grassy fields from sea level up to around 3840m and will make their dens in abandoned burrows, hollow logs or amongst tree roots. The least weasel is a specialist diurnal hunter, preying on predominantly small rodents but will take eggs, lizards, amphibians, worms and even carrion and will store food for the winter months. Populations of least weasel are generally considered stable, however where the species inhabits mainly agricultural land the populations are under threat due to changes in practices.

The Stoat or Ermine (Mustela erminea)

The stoat is very similar in build and movement to the least weasel but is slightly bigger with a total length between 17-32cm and the tail being at least one third of the body length measuring 6.5-12cm and weighing in between 60g and 350g. The summer coat is a sandy-brown colour on the head and back with a white underside that extends to under the jaw and turns white, except for a black tip on the tail, during the winter months with moulting initiated by changes in the seasons, or photoperiodism.

The stoat has a lifespan of approximately ten years in the wild with males reaching sexual maturity at around ten months and females at just a couple of weeks. Mating takes place between April and July with a litter of 6 to 12 kits born after 280 days gestation, as stoats are not monogamous the litter can be of mixed paternity with delayed implantation of fertilised eggs of 9-10 months occurring. The kits are born blind, deaf and covered in a very fine fur, the milk teeth erupt at three weeks with solid food being eaten at four weeks. By five to six weeks, the eyes are open and they have thermoregulation abilities which are absent before this time.

As with the least weasel, the stoat has a circumboreal distribution mainly found in successional or forest-edge habitats from sea level up to 3000m. The stoat is an opportunistic predator, and although their diet predominantly consists of small rodents, they will take prey much larger than themselves mesmerizing it with a “dance” and commonly raids bird nests for eggs. As with the least weasel, the stoat with cache kills if prey is plentiful for times when prey maybe more scarce. On a world wide scale, there are no major threats to the populations of stoats so are considered stable, however on a local scale populations can suffer from unrestricted trapping and timber harvest; but generally speaking populations are controlled by prey availability and diseases.

The European Polecat (Mustela putorius)

European Polecat
Copyright © 2012 Victoria Hillman
The European polecat is the last surviving ancestor of the ferret which was domesticated over 2000 years ago. It varies greatly in size depending on the sub-species of which there are believed to be seven, including the Carpathian polecat (Mustela putorius rothschildi). Body length ranges from 35-46cm in males and 29-40cm in females with the tail making up approximately one third of the body length and they weigh between 0.7-1.8kg. their winter coat brown-black in colour which is brightened by the lighter under fur which often shows through on the back and flanks whereas the summer coat is a lighter, almost faded brownish-grey but lacks the lustre of the winter coat. The face has a bandit like mask of pale fur with a dark brown band across the eyes and is a key feature in distinguishing them from the other mustelids. The front claws measure approximately 6mm, are strongly curved and only partially retractable whereas the hind claws are shorter at 4mm, less curved and non-retractable.

The polecat has a lifespan of approximately six years with both males and females reaching sexually maturity at around six months. Polecats lead a solitary and polygamous life coming together only to mate between March and May although there are no courtship rituals, the male grasps the female by the scruff of the neck and shakes until she becomes limp to stimulate ovulation at which point he will mate with her, unlike other members of the mustelid family implantation of the fertilised eggs happens almost immediately. Following a gestation period of 40-45 days and average litter of five kits are born in May to June blind, deaf and naked weighing 9-10 grams. By one week the kits are covered in a fine, silky white fur which is replaced between three to four weeks by a brownish-grey woolly coat. At three weeks weaning begins and by two to three months the kits are fully independent and at four months they disperse from their mother and the den.

The European polecat has a widespread distribution in the western Palaearctic inhabiting most types of habitats, particularly lowland areas and riparian woodlands but tends to avoid mountainous regions. Although the polecat is a generalist hunter, it predominately feeds on small rodents, followed by amphibians and occasionally birds such as grouse, quail and pigeons. Prey is stalked and seized with a killing bite to the neck, although instinctive this killing technique does require perfecting with practise; it is not uncommon for polecats to cache food during plentiful times. The population trend of the polecat is currently decreasing with threats including road collisions, habitat fragmentation, poisoning and decreases in their prey. Although a Carpathian sub-species has been identified, it has not been fully described with very little actually known about its populations, habitat and behaviours. 

General Threats to these Species

All the mustelid species currently found in the Eastern Carpathians are listed as least concern on the IUCN Redlist with stable populations, with the exception of the Western polecat whose populations are currently declining. However, local populations are subject to decline due to human activities, in particular changes in farming practices and habitat fragmentation and destruction. One of the biggest issues surrounding mustelids in Europe and in particular the Carpathians is that the exact species, numbers and territories of the area are unknown and virtually unstudied.


Evans, P.G.H., Macdonald, D.W., and Cheeseman, C.L. 1989. Social Structure of the Eurasian Badger (Meles meles). Journal of Zoology 218 (4), Pp 587 - 595

Kranz, A., Tikhonov, A., Conroy, J., Cavallini, P., Herrero, J., Stubbe, M., Maran, T. & Abramov, A. 2008. Martes martes. In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.4.<>. Downloaded on 04 April 2011.

Tikhonov, A., Cavallini, P., Maran, T., Krantz, A., Herrero, J., Giannatos, G., Stubbe, M., Libois, R., Fernandes, M., Yonzon, P., Choudhury, A., Abramov, A. & Wozencraft C. 2008. Martes foina. In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.4.
<>. Downloaded on 18 April 2011.

Kranz, A., Tikhonov, A., Conroy, J., Cavallini, P., Herrero, J., Stubbe, M., Maran, T., Fernandes, M., Abramov, A. & Wozencraft, C. 2008. Meles meles. In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.4.
<>. Downloaded on 18 April 2011.

Tikhonov, A., Cavallini, P., Maran, T., Kranz, A., Herrero, J., Giannatos, G., Stubbe, M., Conroy, J., Kryštufek, B., Abramov, A., Wozencraft, C., Reid, F. & McDonald, R. 2008. Mustela nivalis. In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.4.
<>. Downloaded on 18 April 2011.

Reid, F. & Helgen, K. 2008. Mustela erminea. In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.4.
<>. Downloaded on 18 April 2011.

Fernandes, M., Maran, T., Tikhonov, A., Conroy, J., Cavallini, P., Kranz, A., Herrero, J., Stubbe, M., Abramov, A. & Wozencraft, C. 2008. Mustela putorius. In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.4.
<>. Downloaded on 18 April 2011.