North American river otter

Appearance

The North American river otter is a stocky animal of 5 to 14 kilograms, with short legs, a muscular neck and an elongated body that is broadest at the hips. They have long bodies, and long whiskers that are used to detect prey in dark waters. An average adult male weighs about 11.3 kilograms against the female's average of 8.3 kilograms.

Its body length ranges from 66 to 107 centimetres. About one-third of the animal's total length consists of a long, tapered tail. Tail lengths range from 30 to 50 centimetres. Large male North American river otters can exceed a weight of 15 kilograms. It differs from the European otter by its longer neck, narrower visage, the smaller space between the ears and its shorter tail.

A broad muzzle is found on the North American river otter's flat head, and the ears are round and inconspicuous. The rhinarium is bare, with an obtuse, triangular projection. Eyes are small and placed anteriorly. A short, broad rostrum for exhaling and a long, broad cranium define the relatively flat skull. The North American river otter's nostrils and ears close during submersion, keeping water from entering them. Its vibrissae are long and thick, enhancing sensory perception underwater and on land.

The fur of the species is short, with a density of about 57,800 hairs/cm2 in the midback section. The pelage has a high luster and varies from light brown to black. The throat, chin, and lips are grayer than the rest of the body. Fur of senescent river otters may become white-tipped, and rare albinos may occur.

The North American river otter is sexually dimorphic. Males are, on average, 5% larger than females. In Idaho, juvenile, yearling, and adult males averaged 8, 11, and 17% heavier, respectively, than females of the same age. A clinal reduction in size may exist from north to south along the Pacific coast, but not from east to west.

North American river otters live an average of 21 years of age in captivity, but they can reach 25 years of age. In the wild, they normally live about 8 to 9 years, but are capable of living up to 13 years of age.

Status

The North American river otter is considered a species of least concern according to the IUCN Red List, as it is not currently declining at a rate sufficient for a threat category.

Behavior

North American river otters are active year-round, and are most active at night and during crepuscular hours. They become much more nocturnal in the spring, summer, and fall seasons, and more diurnal during winter. They may migrate as a result of food shortages or environmental conditions, but they do not migrate annually. North American river otters only settle in areas that consist of vegetation, rock piles, and sufficient coverage.The North American river otter is more social than most mustelids.

In all habitats, their basic social group is the family, consisting of an adult female and her progeny. Adult males also commonly establish enduring social groupings, some documented to comprise as many as 17 individuals. In coastal areas, males may remain gregarious even during the estrous period of females. Family groups may include helpers, which can be made up of unrelated adults, yearlings, or juveniles.
Male North American river otters disperse from such family groups more often than females. When females leave, they tend to move much further away than males , which tend to move shorter distances. Male North American river otters do not seem to be territorial, and newly dispersing males may join established male groups.

On occasion, groups of unrelated juveniles are observed. North American river otters living in groups hunt and travel together, use the same dens, resting sites, and latrines, and perform allogrooming. In freshwater systems, groups occur most often in autumn and during early winter. From mid-winter through the breeding season, adult females move and den alone. River otters are not territorial, but individual North American river otters of different groups portray mutual avoidance. Home ranges of males are larger than those of females, and both sexes exhibit intra- and intersexual overlap of their domains.Communication among North American river otters is accomplished mainly by olfactory and auditory signals. Scent marking is imperative for intergroup communication. The North American river otter scent-marks with feces, urine, and possibly anal sac secretions. Musk from the scent glands may also be secreted when otters are frightened or angry.

North American river otters can produce a snarling growl or hissing bark when bothered, and a shrill whistle when in pain. When at play or traveling, they sometimes give off low, purring grunts. The alarm call, given when shocked or distressed by potential danger, is an explosive snort, made by expelling air through the nostrils. North American river otters also may use a birdlike chirp for communication over longer distances, but the most common sound heard among a group of otters is low-frequency chuckling.North American river otters are polygynous. Females usually do not reproduce until two years of age, although yearlings produce offspring on occasion. Males are sexually mature at two years of age. The number of corpora lutea increases directly with age.

Habitat

Although commonly called a "river otter", the North American river otter is found in a wide variety of aquatic habitats, both freshwater and coastal marine, including lakes, rivers, inland wetlands, coastal shorelines, marshes, and estuaries. It can tolerate a great range of temperature and elevations. A North American river otter's main requirements are a steady food supply and easy access to a body of water. However, it is sensitive to pollution, and will disappear from tainted areas.

Like other otters, the North American river otter lives in a holt, or den, constructed in the burrows of other animals, or in natural hollows, such as under a log or in river banks. An entrance, which may be under water or above ground, leads to a nest chamber lined with leaves, grass, moss, bark, and hair. Den sites include burrows dug by woodchucks , red foxes , nutria , or beaver and muskrat lodges. North American river otters also may use hollow trees or logs, undercut banks, rock formations, backwater sloughs, and flood debris. The use of den and resting sites is chiefly opportunistic, although locations that provide protection and seclusion are preferred.

Reproduction

North American river otters are polygynous. Females usually do not reproduce until two years of age, although yearlings produce offspring on occasion. Males are sexually mature at two years of age. The number of corpora lutea increases directly with age.

North American river otters typically breed from December to April. Copulation lasts from 16 to 73 minutes and may occur in water or on land. During the breeding, the male grabs the female by the neck with his teeth. Copulation is vigorous, and is interrupted by periods of rest. Females may caterwaul during or shortly after mating. Female estrus lasts about a month per year, and true gestation lasts 61–63 days. Because the North American river otters delay implantation for at least eight months, the interval between copulation and parturition can reach 10–12 months. Delayed implantation distinguishes the species from the European otter, which lacks this feature. Young are born between February and April, and parturition lasts three to eight hours.

In early spring, expectant mothers begin to look for a den where they can give birth. The female otters do not dig their own dens; instead, they rely on other animals, such as beavers, to provide suitable environments to raise their offspring. When the mothers have established their domains, they give birth to several kits. Litter size can reach five, but usually ranges from one to three. Each otter pup weighs approximately five ounces. At birth, the North American river otters are fully furred, blind, and toothless. The claws are well-formed and facial vibrissae long) are present. The kits open their eyes after 30–38 days. The newborns start playing at five to six weeks, and begin consuming solid food at 9–10 weeks. Weaning occurs at 12 weeks, and females provide solid food for their progeny until 37–38 weeks have transpired. The maximum weight and length of both sexes are attained at three to four years of age.

The mothers raise their young without aid from adult males. When the pups are about two months old and their coats grow in, their mother introduces them to the water. North American river otters are natural swimmers and, with parental supervision, they acquire the skills necessary to swim.
The North American river otters may leave the den by eight weeks and are capable of sustaining themselves upon the arrival of fall, but they usually stay with their families, which sometimes include the father, until the following spring. Prior to the arrival of the next litter, the North American river otter yearlings venture out in search of their own home ranges.

Food

Prey is captured with a quick lunge from ambush, or more rarely, after a sustained chase. North American river otters can remain underwater for nearly 4 minutes, swim at speeds approaching 11 km/h , dive to depths nearing 20 m , and travel up to 400 m while underwater. Several North American river otters may even cooperate while fishing. Small fish are eaten at the surface, but larger ones are taken to the shore to be consumed. Live fish are typically eaten from the head.

North American river otters dry themselves and uphold the insulative quality of their fur by frequent rubbing and rolling on grass, bare ground, and logs.

A highly active predator, the North American river otter has adapted to hunting in water, and eats aquatic and semiaquatic animals. The vulnerability and seasonal availability of prey animals mainly governs its food habits and prey choices. This availability is influenced by the following factors: detectability and mobility of the prey, habitat availability for the various prey species, environmental factors, such as water depth and temperature, and seasonal changes in prey supply and distribution in correspondence with otter foraging habitat.

The diet of the North American river otter can be deduced by analyzing either stool obtained in the field, or gut contents removed from trapped otters.
Fish are the primary component of the North American river otter's diet throughout the year. Every study done on the food habits of the North American river otter has identified varying fish species as being the primary component of its diet. For instance, an Alberta, Canada study involved the collection and analysis of 1,191 samples of North American river otter scats collected during each season. Fish remnants were found present in 91.9% of the scat samples. Moreover, a western Oregon study revealed fish remains were present in 80% of the 103 digestive tracts examined. Crustaceans , where regionally available, are the second-most important prey for otters. Crustaceans may even be consumed more than fish. For example, a study conducted in a central California marshland indicated crayfish formed nearly 100% of the river otter's diet at certain times of the year. However, North American river otters, as foragers, will immediately take advantage of other prey when readily obtainable. Other prey consumed by North American river otters includes fruits, reptiles, amphibians, birds , aquatic insects, small mammals, and mollusks.

North American river otters are not scavengers; they avoid consuming carrion. North American river otters do not generally handle prey of a large size relative to themselves but there are occasions where they've been observed ambushing and killing adult common snapping turtles while the large turtles are hibernating. Remains of the much larger North American beaver have been found in North American river otter scat in some regions, although most otter dietary studies in areas where otters and beaver are sympatric do not show them to be regular predators of beavers and perhaps only young beaver kits may be attacked.

North American river otters do not dramatically reduce prey populations in the wild, generally speaking. When a copious supply of food dwindles or other prey becomes available, North American otters either transfer to a new location or convert their dietary choices to the most adequate prey. When left unchecked, though, otter depredations can be quite significant under certain circumstances . Likewise, the potential predatory impact of otters may be considerable whenever fish are physically confined . Resolution of such conflicts will usually require removal and/or relocation of nuisance otters. Even in larger bodies of water, they may take disproportional advantage of any seasonal concentrations of fish when and where only very limited areas of suitable spawning, low-flow, or over-wintering habitat may exist. Even such fast-swimming species as trout become lethargic in extremely cold water, with a commensurate increase in their vulnerability to predation. As such, careful consideration of any threatened, endangered, or fish species of special interest is warranted prior to reintroduction of otters to a watershed. Although other prey species are of temporary significance to the North American river otter, the deciding factor whether the North American river otter can establish itself as a permanent resident of one location is the year-round availability of fish.

Predators

The North American river otter has few natural predators when in water. Aquatic predators include the American alligator, American crocodile, and killer whale, none of which commonly coexist with the North American river otter and thus rarely pose a threat. On land or ice, the North American river otter is considerably more vulnerable. Terrestrial predators include the bobcat, cougar, coyote, domestic dog, wolf, black bear, bald eagle, and red fox.

Evolution

The North American river otter was first described by German naturalist Johann Christian Daniel von Schreber in 1777. The mammal was identified as a species of otter and has a variety of common names, including North American river otter, northern river otter, common otter and, simply, river otter. Other documented common names are American otter, Canada otter, Canadian otter, fish otter, land otter, nearctic river otter, and Prince of Wales otter.

The North American river otter was first classified in the genus ''Lutra''; ''Lutra'' was the early European name. The species name was ''Lutra canadensis''. The species epithet ''canadensis'' means "of Canada".


In a new classification, the species is called ''Lontra canadensis'', where the genus ''Lontra'' includes all the New World river otters.
Molecular biological techniques have been used to determine when the river otter and the giant otter of South America diverged. These analyses suggest they diverged in the Miocene epoch 23.03 to 5.33 million years ago , which is "much earlier" than indicated in the fossil record. Fossils of a giant river otter dating back 3.5 Mya have been found in the US Midwest; however, fossils of the modern river otter did not appear in North America until about 1.9 Mya. The earliest known fossil of ''Lontra canadensis'', found in the US Midwest, is from the Irvingtonian stage . The oldest fossil record of an Old World river otter comes from the late Pliocene epoch ....hieroglyph snipped... The New World river otters originated from the Old World river otters following a migration across the Bering Land Bridge, which existed off and on between 1.8 million and 10,000 years ago. The otters migrated to North America and southwards again across the Panamanian Land Bridge, which formed 3 Mya.