Birth and Care of Young
1. Total gestation is 15 to 16 months.
2. Gestation includes a period of delayed implantation: when the fertilized egg divides into a hollow ball of cells one layer thick (blastocyst), it stops growing and remains free-floating in the uterus for four to five months. The blastocyst then implants on the uterine wall and continues to develop.
3. Delayed implantation ensures that the calf will be born when environmental
conditions are optimal for its survival.
B. Birth seasons.
1. Calves are born mid-April to mid-June, on the northward migration.
C. Frequency of birth.
1. Most pregnancies are spaced at least two years apart for younger females. Older females probably bear calves less often.
2. A female generally gives birth to a single calf at a time. Twins are rare, although
they have been reported.
Calves are usually born on the ice.
1. Newborn calves weigh about 45 to 75 kg (99-165 lb.) and are about 95 to 123 cm (3-4 ft.) long.
2. Calves are ashen gray to brown with dense, short soft fur. About two to three months before birth, the calf sheds a fine white layer of soft fetal hair called the lanugo.
3. Within days or weeks, the calf becomes more robust. Its fur turns reddish-brown to
tawny within one to two weeks. Calves shed and replace their natal coat when they are one
or two months old. This first molt is usually completed by August. Calves then molt
a. Calves may nurse for as long as two years. Some may nurse even longer, if the mother does not have a new calf.
b. Walrus milk is about 30% fat, 5% to 10% protein, and 60% water, with traces of carbohydrates. The composition of milk remains relatively constant throughout the nursing period.
c. Nursing usually takes place in the water, but sometimes occurs on ice or land.
d. Milk is occasionally supplemented with solid pieces of food as early as six months of age. Most calves, however, rely primarily on milk for the first two years.
e. In a zoological environment,calves nurse about six to ten times per day. Orphaned calves are fed a formula of cream, ground fish and clams, proteins, milk replacer (Multi-milk), vitamins, and water. They consume up to 17.9 liters (300 oz.) per day. There is no information available on the frequency of nursing or the volume of milk consumed by a calf in the wild.
2. Cows with calvesmore than two days old tend to gather in herds separate from the bulls and other females. These "nursery herds" usually include 20 to 50 individuals but may include as many as 200 walruses.
3. A cow is extremely protective of her calf. She defends and protects her calf and may shelter it under her chest between her foreflippers. Calves often ride on their mothers' backs in the water.
4. There is some evidence that females may care for orphans, although it is unknown
whether the female nurses the orphan.
G. Calf growth and development.
1. The calf grows about 10 to 15 cm (4-6 in.) in length each month. In a zoological environment, a calf gains 0.7 to 0.9 kg (1.5-2 lb.) per day. Growth rates gathered in zoological environments are considered to be indicative of the growth rates of free-living walruses. Males grow slightly faster than females.
2. By one month of age, calves are strong swimmers.
3. A pregnant, near-term cow and her calf from the previous pregnancy usually separate in late April, just before the new calf is born. Mother and calf stay together two years or longer if the mother doesn't produce another calf. Young males may stay an additional two or three years before joining an all-male herd. Females tend to stay with the same herd.
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