Reproduction

Data, statistics, and information regarding the reproductive history of Odobenus rosmarus in captive settings.

Preface

Please keep in mind that unless otherwise noted, this page references studies and sources that pertain specifically to observations in captive walruses. The events described here may differ from or be entirely independent of occurrences in wild populations, and I highly recommend consulting alternate sources if your aim is to learn about the life history of this species in the wild.

This page is largely reliant upon information made available to the general public, and therefore is subject to inaccuracies and incomplete data. The information presented here has been made as accurately as these restrictions allow and is up to date as of December 26th. 2024. 

Information

Maturity

The largest percentage of both bulls and cows conceive their firstborn calves at ten years of age.

At least one captive bull began displaying rut behaviors and spermatogenesis at five years of age; however, it was only when the cow with which he was housed went into estrus at nine years old that the pair were first observed copulating, successfully conceiving the following year when both were ten.

 The youngest captive female to give birth was seven at parturition, with conception taking place when the individual was six; the youngest bulls were ten at the birth of their first calves.

Mating

Walruses are seasonal breeders, with captive animals having been observed mating from November through to May, with a peak in mating behaviors taking place in February.

Gestation

Pregnancies in walruses last 14 to 16 months; gestations in captivity with known conception dates have lasted from 427 to 483 days. Pregnancies begin with a delayed implantation period during which the fertilized egg floats freely in the uterus — development of the egg doesn't begin until implantation into the uterine wall after four or five months.

There has been a single recorded case of fetal retention in captive walruses, in which a pup due in May of 2003 was stillborn six months later, totaling approximately 20 months of pregnancy for the cow.

Birth

Walruses calve seasonally, with liveborn captive pups having been delivered from March to July; the vast majority of young, at 78%, are born in May and June, with births peaking in the latter month. At least two known pregnancies were delivered in August, although I have no information on whether or not the resultant pups were alive at birth.

On average a captive female will have a three year interval between births; the longest pregnancy interval recorded to date lasted ten years.

Offspring

Typically walruses will give birth to a single pup, although six cases of twins have been recorded in captive specimens (accounting for over 7% of all known pregnancies). Only one of these twelve pups was known to be liveborn, though the individual survived only two days post-parturition. Of the four cows who have delivered twins, two immediately passed away from uterine torsion; one of the two surviving cows went on to deliver healthy calves from uncomplicated pregnancies, while the other cow delivered three consecutive twin pregnancies after two singletons.

One mother-raised captive-born pup that was studied had a nursing period lasting 19 months; another study states that pups nursed for two to three years, up until the cow's next offspring were calved. Walrus calves born from Species Survival Plan recommendations in AZA-accredited facilities are expected to remain with their mothers for a minimum of two years, barring unforeseen circumstances affecting the wellbeing of the calf.

Senescence

Studies of wild walruses indicate that females reach the end of their reproductive lifespan by the age of thirty, and the captive population tentatively follows this data, with the oldest female known to have given birth having been 29 years old. At least one female was still ovulating at the age of 36, but no cow known to me at this time has conceived a pup after age 28.

The oldest bulls to reproduce were 36 years old at the conception of their last calves.

Statistics

Pregnancy

An absolute minimum of 82 pregnancies resulting in 88 pups have been verified from 35 captive cows, with the first pregnancy occurring in 1971.

Pregnancies have taken place across three continents (38 totaling 46% from North America, 33 totaling 40% from Asia, and 12 totaling 14% from Europe), nine countries, and 24 facilities.

Birth

Please note that, due to the adherence of non-transparency so heavily prevalent among the vast majority of zoological facilities, this data may lean more heavily towards a higher percentage of liveborns and higher survival rates than may factually exist. I have also opted at this time to exclude pregnancies which have been visually suspected but not officially confirmed through any published statements, publications, or direct communication by the relevant facilities and/or employed persons.

Of the 88 known calves, 54 totaling 61% survived parturition, 13 totaling 15% were stillborn, 5 totaling 6% were miscarried, and 13 totaling 15% of all deliveries had unknown results. At least 3 died in-utero when their mother passed during pregnancy or birth, totaling 3% of calves.

Of the 54 known liveborn pups, at least 36 totaling 66.7% survived their first year of life.

References

Please note that this section was added well after the creation of this page, and the sources used are still being sought out and collected so that they may be properly cited here. I thank you for your patience and understanding as I strive to transform Walrus Network into a more professional space.