A. Gestation.

Gestation period is about 12 months (Schroeder, 1990; Hansen, 1990; Odell, 1975).

B. Birth seasons.

1. Worldwide, calves are born throughout the year (Schroeder, 1990; Hansen, 1990; Odell, 1975).

2. Seasonal calving peaks vary by area (Schroeder, 1990; Hansen, 1990; Odell, 1975).

a. Bottlenose dolphins along the west coast of Florida show a calving peak in May (Urian, et al., 1996).

b. Most dolphin births along coastal Texas waters occur in March (Urian, et al., 1996).

c. Peak calving appears to be bimodal for dolphins in Florida's Indian River Lagoon; most births occur in April and August (Urian, et al., 1996).

d. Bottlenose dolphins in the Pacific Ocean along the coast of southern California have shown a calving peak in the fall.

C. Frequency of birth.

A female dolphin caon potentially bear a calf every two years, but calving intervals generally average three years.

D. Calving.

1. Calves are born in the water. Deliveries can be either tail-first or head-first. The umbilical cord snaps during or soon after delivery.

2. Sometimes an assisting dolphin may stay close to the new mother and calf. Although this assisting dolphin often is referred to as an "auntie" dolphin, it may be male or female. This "auntie" dolphin is often the only other dolphin a mother allows near her calf (Herman, 1980).

E. Calf at birth.

1. The calf is approximately 106-132 cm (42 to 52in.) long and weighs about 20kg (44 lb.).

2. In the first few days after birth, the dorsal fin and tail flukes are flaccid and pliable, but gradually become more stiff.

3. Calves are darker than adults and show several vertical, light-colored lines on their sides, a result of fetal folding. These lines disappear within six months.

The light-colored lines on the sides of a dolphin calf are a result of fetal folding.

F. Care of the young.

1. Nursing.

a. Calves nurse under water, close to the surface.

b. The calf suckles from nipples concealed in abdominal mammary slits.

c. Observations in zoological parks show that nursing usually begins within six hours of birth. A calf nurses as often as four times per hour for the first four to eight days (Schroeder, 1990).

d. Each nursing instance usually lasts only about five to ten seconds. A calf nurses three to eight times per hour throughout the day and night (Cockcroft and Ross, 1990).

e. Milk is composed of 33.0% fat, 6.8% protein, and 58.3% water (Oftedal, 1984), with traces of lactose. The rich milk helps the baby rapidly develop a thick insulative layer of blubber.

f. A calf may nurse for up to 18 months (Barros and Odell, 1990).

2. A mother dolphin 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," the hydrodynamic wake that develops as the mother swims. This helps the baby to swim and enables the mother and calf to stay up with the group.

3. There is probably a considerable amount of learning involved in mothering.

G. Calf development.

1 . Bottlenose dolphin breeding colonies in marine zoological parks continue to provide a unique opportunity to observe and quantify aspects of dolphin biology.

2. In zoological environments, calves begin to take a few fish at about three to four months, when their teeth begin to erupt. Calves begin to eat fish when they reach about 130 to 150 cm (51-59 in.) (Barros and Odell, 1990).

3. Within a few days of birth a calf can vocalize, but signature characteristics develop with age (Caldwell, Caldwell, and Tyack, 1990).