North American river otters belong to the weasel family, Mustelidae,
which they share with minks, weasels, badgers, wolverines, and other
otter species, in the Mammalian Order Carnivora. Its scientific name
is Lontra canadensis, which means "otter belonging to Canada",
although this otter species range includes much more of North
America than Canada.
photo M Noonan
The North American river otter is considered a medium to large sized
otter, with adults ranging in length from 3 to 5 feet and weighing
between 10 and 30 pounds. The fur on their backs is generally dark
brown, and their undersides vary from light brown to gray. Some
individuals may have a silver or white throat patch. They are
very quick animals, both on land and in the water. North American
river otters are capable of swimming at speeds of seven miles per
hour, and can reach 18 miles per hour at a full run. The life
expectancy for this species in the wild is only about ten years, but
with the steady food supply and protection that zoos afford, captive
individuals can live to be twenty years old.
The North American river otter is quite possibly the most numerous
otter species in the world. Their range extends through most of
North America from Alaska and northern Canada down to southern
Florida. These animals inhabit a variety of diverse environments,
from saltwater estuaries to freshwater lakes, rivers, marshes and
streams. The bulk of these animal’s diets consist of slow-swimming
fish and small crustaceans, but they are also very opportunistic
hunters. North American river otters will eat frogs, turtles,
snakes, insects, small mammals and birds whenever this type of prey
is readily available.
North American river otters very vocal, and the animals use a variety of calls
to communicate. The calls may range from high-pitched chirps,
whistles and twitters, to low grunting chuckles and buzzes.
This species is highly inquisitive and playful.
They have been observed using muddy riverbanks and snow drifts as
slides, rushing down on their bellies and slipping into the water.
The skills they build during their frequent play sessions later
serves them well when they need to make quick escapes from predators such as wolves or coyotes.
Other “play” behaviors help these animals find food. For example,
North American river otters have been observed swimming in circles
to create a small whirlpool. The suction created by the whirlpool
pulls hiding fish up from the bottom of a river or stream.
Reproduction in North American River Otters is highly seasonal.
Females are in estrus for approximately 1 month per year, and males
start sperm production and have increased testosterone levels for
approximately 3 months per year. Additionally, there is some
evidence that seasonality is related to geographic location in that
those in more southern latitudes start estrus and testosterone
increases much earlier in the year than those in northern latitudes.
This geographic influence also extends to parturition, where
females with give birth at earlier times in more southern latitudes.
The North American
River Otter is one of only two known otter species to have delayed
implantation (the other is the Sea Otter). Fertilized eggs will
remain in diapause for 7-10 months before implanting - usually
during late winter/early spring months. Once the embryos implant
the gestation period is fairly consistent at 68-73days. The total
resulting duration of pregnancy (from date of last observed breeding
to parturition) is thus 302-351 days.
Females do not usually excavate dens; instead,
they prefer to use abandoned dens of other animals or naturally
existing shelters. The typical litter is 2-3 kits, but there may be
as many as six kits in a single litter. The kits are only about 4.5
ounces at birth, and they cannot swim until their dense undercoats
grow in at about two months of age. When they are learning to swim,
the kits sometimes climb onto their mother’s back. Young will leave their mother when they
are about one year old, and they will
reach maturity between two
and three years of age.
photo M Noonan
Fossils of the North American river otter have been dated back to
the Pleistocene period. They were well established throughout their
range, as they have few natural predators. Native Americans hunted
them for their warm, dense fur, but the number of animals taken was
not high enough to impact the size of their populations. The real
trouble for these animals began with the arrival of the Europeans in
the Americas. Extensive hunting drastically reduced their numbers in
the wild, and North American river otters vanished from some states
entirely. There are a number of examples of Native American folklore
involving the otter. Several origin myths place the otter as one of
the animals sent down to the bottom of the water to find earth, upon
which all the seeds of life are then planted. The otter is also
frequently portrayed as carefree, comical, or lazy. Sometimes, even
as a rather obnoxious character. In a Shoshone myth, Otter mocks
Beaver for working too hard. Beaver’s wounded pride causes him to
prove that he can slide farther than Otter. Beaver slides down a
mountain on his tail, to which a laughing Otter replies, “The slide
was perfect, but look what you have done to your tail!”
While North American river otters are not endangered, their
populations are still threatened by humans. It is still legal to
trap river otters in 38 states, and anywhere from 20,000 to 30,000
individuals are killed each year for their pelts. Apart from the fur
trade, the two largest threats to these animals are habitat
destruction and water pollution. Despite the wide variety of
habitats in which the North American river otter can be found, they
are particularly shy animals and will try to avoid human contact in
the wild. As human populations develop areas in which wild otters
live, the animals are forced into smaller and smaller territories.
They are also incredibly sensitive to pollutants, and otter
populations have suffered declines around human settlements and
As the otters began to disappear from their historical ranges, steps
were taken to help slow the rate of decline. Several states in which
the otters were entirely wiped out now have budding populations
thanks to reintroduction programs. In the 1980’s, the North American
river otter was rare or extinct in 26 states. Today, that number has
been reduced to fifteen. Zoos and wildlife rehabilitation centers
all across the country are partnering in breed and release programs
to help further the recovery of these energetic animals.