Subject: Info: Birth and Care of Young

Michael Williamson (williams@whale.simmons.edu)
Fri, 19 Apr 1996 19:43:25 -0500

> Birth and Care of Young
> 
> A. Gestation.
> 
> 1. Gestation periods range from 10 to almost 14 months depending on
> the species and are linked to the annual migration cycle.
> 
> 2. A pregnant female's energy needs increase greatly during the second
> half of the gestation period. Pregnant females of some species
> increase their food intake by as much as 50% to 60% above normal
> during the last six months of pregnancy. Excess energy is stored until
> it is spent during lactation.
> 
> 3. Newly pregnant females are usually the first to leave the breeding
> grounds and first to arrive in the summer feeding grounds.
> 
> B. Birth seasons.
> 
> 1. Most species of baleen whales exhibit a seasonal breeding cycle,
> giving birth primarily during the winter and spring in sub-tropical to
> tropical breeding grounds.
> 
> 2. Giving birth in warmer water reduces the energy requirements on a
> newborn to stay warm while it develops an insulating blubber layer.
> 
> 3. Near-term pregnant females are usually the first to arrive in the
> calving grounds.
> 
> C. Frequency of birth.
> 
> 1. Baleen whales give birth to a single calf. Twins are extremely
> rare. If twins are conceived, they are unlikely to survive to full
> term. In rare cases where twins are born, they are not likely to
> survive, due to a limited milk supply from the mother.
> 
> 2. In most species, females may bear a calf every two to four years.
> 
> D. Calving.
> 
> 1. Observations of baleen whale births at sea are extremely rare. The
> usual delivery seems to be tail-first, but a few head-first deliveries
> have been documented.
> 
> 2. The placenta seperates from the uterine wall during or soon after
> delivery.
> 
> 3. Some species seek protected coastal areas to give birth.
> 
> E. Calf at birth.
> 
> 1. Calves can swim at birth.
> 
> 2. Baleen whale calves range from about 1.5 m (5 ft.) for pygmy right
> whales to about 7 m (23 ft.) for blue whales.
> 
> 3. In general, a calf is approximately one-quarter of the mother's
> length.
> 
> 4. Birth weight is approximately 3% to 4% of the mother's weight. Blue
> whale calves weigh about 2,700 to 3,600 kg (6,000 to 8,000 lb.) at
> birth.
> 
> 5. Baleen whale calves have small, soft baleen plates. See also
> baleen.
> 
> F. Care of young.
> 
> 1. Nursing.
> 
>      a. The nursing period lasts from 4 to 11 months. A calf is weaned
>      by its first summer in time to feed.
> 
>      b. The calf suckles from nipples concealed in its mother's
>      abdominal mammary slits. Calves nurse under water, close to the
>      surface.
> 
>      c. A high fat content (up to 40% to 50% fat) allows the calf to
>      rapidly develop a thick insulating layer of blubber.
> 
> 2. All species of baleen whales establish strong mother/calf bonds.
> The pair stay in close physical contact throughtout the nursing
> period.
> 
>      a. A mother baleen whale stays close to her calf and attentively
>      directs its movements. The baby swims close to its mother and is
>      carried in the mother's "slip stream," a type of hydrodynamic
>      wake which develops as the mother swims.
> 
>      b. The mother may teach the calf certain behaviors.
> 
>      c. Whalers noticed that females became aggressive when protecting
>      their young.
> 
> 3. There is probably a considerable amount of learning involved in
> mothering and teaching the calf.
> 
> 4. Calf development rates vary by species.
> 
>      a. Sei whales are 4.5 m (15 ft.) at birth and grow about 2.5 cm
>      (1 in.) each day.
> 
>      b. Blue whale calves gain 90 kg (200 lb.) each day while nursing.
> 
>      c. Gray whale calves double their weight in about three months
>      and double their length in about two years.
> 
>      d. Humpback whales grow 45 cm (1.5 ft.) per month during nursing.
> 
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