Timing of Major Life History Events
Breeding - Northern river otters breed in late winter or early spring; the
breeding season is spread over a period of 3 months or longer [1,4].
Gestation period and litter size - There is much discrepancy in the
literature regarding the length of gestation in the northern river otter.
Gestation periods of 288 to 375 days have been reported. The extreme
length of gestation is due to a process called "delayed implantation",
wherein the development of the blastocyst is arrested for a period of
time before it implants into the uterine wall. Litters are generally
born from November through May. In northwestern North America, river
otters generally give birth from March through May following an average
delay of 9 months and an actual gestation of about 62 days . Litter
size ranges from one to six, with two to four young most common .
Pup development - Northern river otter pups are born helpless. They begin to
open their eyes by age 21 to 35 days; by 25 to 42 days pups begin
playing. Northern river otter pups are introduced to water by age 48 days and
may venture out of the den on their own by the age of 59 to 70 days.
Weaning occurs at about 91 days of age .
Age at sexual maturity - Female northern river otters normally become sexually
mature when they are about 2 years old, but may or may not breed at that
time. Female northern river otters may not breed every year [6,14]. Although
male northern river otters also become sexually mature at about 2 years of age,
they may not become successful breeders until they reach 5 to 7 years
Life span - Northern river otters have lived at least 16 years in captivity .
Northern river otters are primarily nocturnal, but may be active in the early
morning and late afternoon in remote areas. They are active all winter
except during the most severe periods, when they take shelter for a few
- 1. Banfield, A. W. F. 1974. The mammals of Canada. Toronto, ON: University of Toronto Press. 438 p. 
- 4. Chapman, Joseph A.; Feldhamer, George A., eds. 1982. Wild mammals of North America. Baltimore, MD: The Johns Hopkins University Press. 1147 p. 
- 6. Dronkert-Egnew, Ana E. 1991. River otter population status and habitat use in northwestern Montana. Missoula, MT: Univeristy of Montana. 112 p. Thesis. 
- 14. Melquist, Wayne E.; Hornocker, Maurice G. 1983. Ecology of river otters in west central Idaho. Wildlife Monographs. 83: 1-60. 
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