By Matt Wund
Carnivora and is comprised of 56 species in 22 genera. Members of this family include weasels, stoats, polecats, mink, marten, fishers, wolverines, otters, badgers and others. While many authors have traditionally considered skunks a subfamily within , recent molecular evidence indicates that skunks do not lie within the mustelid group and instead are recognized as a single family, Mephitidae, a systematic understanding which is accepted here (Dragoo and Honeycutt, 1997; Flynn et al., 2005; Marmi et. al., 2004; Sato et. al., 2003; Sato et. al., 2004). (Dragoo and Honeycutt, 1997; Flynn et al., 2005; Marmi, Lopez-Giraldez, and Domingo-Roura, 2004; Nowak, 1991; Sato et al., 2003; Sato et al., 2004; Vaughan, Ryan, and Czaplewski, 2000; Whitaker and Hamilton, 1998)is the largest family within
Mustelids inhabit all continents except Australia and Antarctica, and do not occur on Madagascar or oceanic islands. Members of this group can be found in diverse habitats, which include both terrestrial, aquatic and marine environments. Mustelids are mainly carnivorous, with various members of the family exploiting a great diversity of both vertebrate and invertebrate prey. Mustelids are generally proficient hunters; some weasels can take prey larger than themselves. Members of this family often hunt in burrows and crevices, and some species have evolved to become adept at climbing trees (e.g., marten) or swimming (e.g., sea otters, mink) in search of prey. (Nowak, 1991; Sato et al., 2003; Vaughan, Ryan, and Czaplewski, 2000; Whitaker and Hamilton, 1998)
Generally, mustelids have elongate bodies with short legs and a short rostrum, as typified by weasels, ferrets, mink, and otters. Wolverines and badgers have broader bodies. An order of magnitude difference in size exists between the smallest and largest mustelid species. The smallest species is the least weasel (Mustela nivalis), weighing between 35 and 250 grams. Wolverines (Gulo gulo) and sea otters (Enhydra lutris) reach 32 kg and 45 kg, respectively. All mustelids have well developed anal scent glands, which serve various functions, including territorial marking and defense. (Hutchings and White, 2000; Nowak, 1991; Vaughan, Ryan, and Czaplewski, 2000)
Other Geographic Terms:
Systematic and Taxonomic History
There has been much debate regarding the relationships among various groups groups within Mustelinae), badgers (Mustelinae), honey badgers (Mustelinae), otters (Lutrinae), skunks (Mephitinae), and all other weasel-like mustelids (Mustelinae). Recent molecular evidence has shown that skunks do not lie within , and thus skunks have been elevated to the family Mephitidae. The position of other taxa within have also been subject of recent debate (e.g., Gulo). Furthermore, the systematics of red pandas (Ailurus fulgens) has been controversial, with this species being placed alternately within Ursidae or Procyonidae. Recent comprehensive molecular studies of Carnivora, however, indicate a relatively close relationships between Ailurus and stink badgers ( ) (Flynn et al., 2005). (Dragoo and Honeycutt, 1997; Flynn et al., 2005; Sato et al., 2003; Wilson and Reeder, 1993). Between four and seven subfamilies have been recognized in the past. Currently up to six subfamilies are generally accepted: Old World badgers (
The morphological characters considered to unite all mustelids are enlarged anal scent glands, the loss of the second upper molar, and the loss of the carnassial notch on the fourth upper premolar. Mustelids share these characters with skunks, the main reason for their historical inclusion in the family. These characters may be the result of convergent evolution, however. For example, all carnivores have enlarged scent glands, and those of skunks are much more enlarged than in . Furthermore, the anal scent gland in skunks is associated with a nipple, rather than a duct as in . (Dragoo and Honeycutt, 1997; Flynn et al., 2005; Koepfli and Wayne, 2003; Marmi, Lopez-Giraldez, and Domingo-Roura, 2004; Sato et al., 2003; Sato et al., 2004)
- enlarged anal scent glands
- loss of the carnassial notch on the 4th upper premolar
- loss of a second upper molar
- Molecular synapomorphies resulting from phylogenetic analysis of a suite of genes: the nuclear genes transthyretin intron I (TR-i-I), thyroxine-binding globulin (TBG), interphotoreceptor retinoid-binding protein (IRBP), nuclear recombination-activating gene 1 (RAG1), and five nuclear gene segments amplified with type I sequence-tagged site (STS) primers (Koepfli et. al., 2003); and the mitochondrial genes NADH-ubiquinone oxidoreductase chain 2 (ND2), cytochrome-b, and 12S and 16s ribosomal RNA.
Adult mustelids range in size from 114 mm and 25 g (least weasel) to over 1 m and 45 kg (sea otters). These animals are generally long-bodied with short legs. Most species have slender bodies, but some, like badgers (Mustelinae, Mustelinae) and wolverines have much broader bodies. The skull is elongate with a relatively short rostrum. Adult males are generally about 25 percent larger than females of the same species. The ears are short, as are the legs, each of which bears five digits. The claws do not retract and, in digging species, are especially robust. Mustelids are digitigrade or plantigrade. The dental formula varies among species: 3/3, 1/1, 2-4/2-4, 1/1-2 = 28-38. The canines are long, and the carnassials are well-developed. The upper molars are often narrow in the middle, giving them an hourglass shape. Mustelids have a powerful bite; in many species, the large postglenoid process locks the lower jaw into the upper, causing the lower jaw to only move in the vertical plane, without any rotary motion. (Nowak, 1991; Vaughan, Ryan, and Czaplewski, 2000; Whitaker and Hamilton, 1998)
Sexual dimorphism: male larger.
Mating systems vary both within and among species. Many species are polygynous and/or promiscuous. Some species are social, while others are solitary. Social organization can vary within species as well. Mustelids require prolonged periods of copulation to induce ovulation of an unfertilzed egg. As a result, copulation may last for several hours before fertilization can be successful. (Amstislavsky and Ternovskaya, 2000; Johnson, MacDonald, and Dickman, 2000; Vaughan, Ryan, and Czaplewski, 2000)
Most mustelids breed seasonally, but the length of the reproductive period varies among species. Day length often dictates the onset of the breeding season, which usually lasts 3 to 4 months. Many mustelids undergo delayed implantation, with the fertilized embryo taking up to 10 months (e.g. Meles meles) to implant in the uterus in some species. Environmental conditions such as temperature and day length determine when implantation occurs. Mustelids that live in more seasonal climates are more likely to exhibit delayed implantation. Following implantation, gestation typically lasts 30 to 65 days. Females give birth to a single litter each season, the size of which varies within and among species. For example, sables have an average litter size of 2.2, but can give birth to anywhere from 1 to 7 pups. The mountain weasel averages 8.7 pups per litter, but can have between 3 and 14 young in a single bout of reproduction. Generally, mustelids are altricial, being born small and blind. They reach sexual maturity between 8 months and two years following birth. (Amstislavsky and Ternovskaya, 2000; Nowak, 1991; Thom, Johnson, and Macdonald, 2004; Vaughan, Ryan, and Czaplewski, 2000)
Young are generally born in an alricial state, requiring extenisive care and protection from their mother. Young mustelids typically are able to care for themselves when they are about two months old. Females defend territories in order to acquire enough resources to care for their young and most often nurse and protect them in a burrow or den. (Johnson, MacDonald, and Dickman, 2000; Nowak, 1991)
altricial ; precocial ; pre-fertilization (provisioning, protecting: female); pre-hatching/birth (provisioning: female, protecting: female); pre-weaning/fledging (provisioning: female, protecting: female); pre-independence (provisioning: female, protecting: female).
Mustelids typically live between 5 and 20 years in the wild. (Nowak, 1991)
Social behavior varies both within and among species, and may vary in relation to local environmental conditions such as food availability. For example, European badgers are known to form groups with several males and females that are all reproductively active within the group. Yet in other parts of their range, European badgers may live solitarily or in pairs.Many species are territorial for at least part of the year, with individuals competing over hunting areas or access to mates (e.g., Mustela erminea). (Johnson, MacDonald, and Dickman, 2000)
Communication and Perception
Other communication keywords:
scent marks .
Mustelids are primarily carnivorous, but some species may at times eat plant material. A wide range of animal taxa are preyed upon by various members of this family; many mustelids are opportunistic feeders rather than specialists. However, many mustelids are especially adept at capturing small, mammalian prey. Weasels, for example, are capable of chasing and capturing rodents in their burrows. Otters are well-adapted to chasing and capturing aquatic prey, including fish, crustaceans, and other aquatic invertebrates. Mustelids hunt in a variety of terrestrial, aquatic, and arboreal habitats. Some species regularly prey on animals larger than themselves. Some species have been known to store food (e.g., Mustela, Gulo). (Nowak, 1991; Vaughan, Ryan, and Czaplewski, 2000)
stores or caches food .
Mustelids are generally small carnivores, and are therefore subject to predation by larger carnivores such as canids with which they co-occur. They may also fall prey to large snakes (Serpentes), raptors (Falconiformes), and owls (Strigiformes). Some mustelids secrete noxious chemicals to discourage predators. In some of these species, aposematic color patterns can help ward off predators. (Bright, 2000; Nowak, 1991)
Mustelids mainly impact their communities through their effects on prey populations. Many species limit rodent and bird populations. In some cases, mustelids limit rodents that are considered pests, in other cases, mustelids threaten rare bird species. Some species, such as sea otters ( ) are keystone predators, enhancing the diversity of their community by keeping highly competitive prey species in check. Honey badgers (or ratels, Mellivora capensis) have developed commensal relationships with both humans and honey guides (Indicator indicator), using both to aid in the location of bee colonies. (Bright, 2000; Macdonald and King, 2000; Nowak, 1991)
Key ways these animals impact their ecosystem:
keystone species .
Economic Importance for Humans: Negative
Some mustelids are considered pests, either for harming poultry livestock, for threatening other species in the wild, or for transmitting diseases. European badgers have been implicated in the transmission of bovine tuberculosis. Cattle may become infected from grazing on land where badgers have defecated. Up to 20% of badgers carry the disease in areas where bovine tuberculosis is a problem. Since 1975, badgers have been culled in the United Kingdom, but there is no conlcusive evidence that it has helped control bovine TB. As mammalian carnivores, mustelids can also be infected by, and transmit, rabies. (Bright, 2000; Gough and Rushton, 2000; Nowak, 1991)
Ways that these animals might be a problem for humans:
causes or carries domestic animal disease .
Economic Importance for Humans: Positive
Many mustelids help control rodent populations that are considered to be pests. In addition, many are hunted and/or raised for their pelts, which are often considered highly valuable (e.g., the pelts of mink and sable). Some species have been domesticated and are traded as pets (e.g., ferrets). (Bright, 2000; Nowak, 1991)
Ways that people benefit from these animals:
pet trade ; body parts are source of valuable material; controls pest population.
Some mustelid species are considered highly threatened by the IUCN, while other species are so abundant that they are considered pests. Approximately 38% of all species of otters and martens. Smaller carnivores that are restricted to small habitat fragments may also be at risk to predation by larger carnivores that can more easily move among fragments. Hunting has been a problem for some species, while others, particularly tropical mustelids, do not seem to be declining as a result. Endangered mustelids include: Colombian weasels ( ), European mink (Mustela lutreola), Indonesian mountain weasels ( ), marine otters (Lontra felina), southern river otters (Lontra provocax), sea otters (Enhydra lutris), and giant Brazilian otters (Pteronura brasiliensis). Sea mink ( ) became extinct in recent times. (Bright, 2000; Gough and Rushton, 2000)are considered threatened,which is a much higher proportion than mammals in general (15%). Habitat destruction is a serious risk to species with restricted habitat requirements such as
Numerous re-introduction programs for various mustelid species have met with mixed success. Generally, "soft" re-introductions, those that allow the animals to acclimate to their new surroundings while in a temporary enclosure, are more successful than "hard" re-introductions, in which captive-bred animals are released directly into the wild. Black-footed ferrets (Mustela nigripes) are considered extinct in the wild, although several re-introduction programs are underway. (Bright, 2000)
Matt Wund (author).
Tanya Dewey (editor), Animal Diversity Web, University of Michigan Museum of Zoology.