As far as we know today, the
birth of a dolphin in the wild has never been observed. All we know about the dolphin birthing process has been learned by
our observation of captive animals.
The time
required for males and females to reach sexual maturity differs by gender and by geographic location. Male dolphins reach
sexual maturity at anywhere from 10-15 years of age, with females reaching sexual maturity at 5-13 years. But, obtaining
sexual maturity is more a function of size, not age. Females reach sexual maturity when they are about 85-95% of their adult
body length. Female dolphins are believed to spontaneously ovulate, not having a set ovulation cycle. Typically, they will
ovulate anywhere from one to six times per year. Ovulation often is stimulated by the presence of a male dolphin or may occur
in a mother following the loss of her calf. Dolphins are not monogamous. They will have several breeding partners in a given
reproductive season. Other than humans and chimpanzees, dolphins are the only other animal that engages in sexual activity
for reasons other than reproduction and not timed specifically with female estrus. Male Bottlenose dolphins will perform sex
acts with other dolphin species as well as with other males of their own species. Male-to-male sexual activity (called "intromission")
among dolphins is often a sign of bonding, recreation or even aggression.
Two or more
males will often "herd" females for purposes of mating and to keep them from having access to other potential male partners.
Should the female not be interested in such advances, she will roll ventral side up or will roll away from the male
to the opposite side, preventing the male from mounting her. Females have been observed working cooperatively with other females
to help one another escape being herded by males.
Courtship between
male and female dolphins involves much contact including head-butting and raking (using their teeth to rake or scratch each
other). Erection is a voluntary activity by the male dolphin. The male dolphin’s erect penis is pointed for easy insertion
into the female and does not require stimulation to release sperm. The penis faces forward during erection to facilitate coitus.
The female rolls on one side, presenting her ventral side to the male. The release of sperm occurs while swimming and
is very rapid (occurring in about 10 seconds) and requires little stimulus. In captivity the dolphin's ability to
ejaculate rapidly and without much stimulus aids animal care workers in the collection of semen samples "on command" to
be used for health assessment purposes. Following successful fertilization, the fetus will take the next 12 months to
develop to full term. The Bottlenose dolphin shows peak caving activity in the warmer summer months; so it must be assumed
that peak successful mating activity occurs in those months as well.
Signs
of impending birth with the pregnant female include apparent discomfort, hunching up of the body (termed "flexing" or "crunching"),
irregular breathing, irritability, an increased tendency to move objects around in her environment, solicitation of physical
contact with trainers (in captivity), swimming upside down, rolling, breaching, rapid swimming, decreased rectal temperature,
decreased appetite, contractions, vaginal discharge, and lactation. Precautions
for trainers to observe with captive dolphins nearing parturition (separation of the calf from the mother during birth) include
keeping the social group stable, removing sharp edges and structures in the birthing area, and establishing 24 hour watches
both before and after birth. Handling the newborn calf is usually avoided unless the trainer is presented with an
emergency situation.
Following the male's successful impregnating
of the female, gestation lasts 12 months. During this period as the fetus grows, its tail flukes and dorsal fin
(containing fibrous connective tissue) remain folded against its body inside the mother's uterus and are soft at birth, but
will stiffen at about 2 weeks after birth. This is helpful in allowing the calf to more easily exit the mother’s
body during birthing.
Dolphins typically carry single calves and go through the same labor process
as other mammals. Birth takes place in the water while the mother is swimming and is usually "flukes first", although "head
first" births have been observed. Birth weight is about 20-25 pounds with a length of 2-3 feet. Once the calf is out of the
uterus the female quickly snaps off the umbilical cord and typically helps the calf to the surface for its first breath of
air.
The dolphin mother-calf bond is so strong that, should the calf be still
born, females have often been seen holding their dead calves at the surface of the water.
The calf soon learns to swim near its mother both to
nurse and to "slip stream", or remain in the low pressure area the mother creates as she swims (slightly above or below the
mother and to one side). This conserves the calf's energy required for rapid growth. Slip streaming also allows the calf,
yet without a layer of blubber to provide buoyancy, to swim in a controlled, upright manner.
Calves
will nurse for as long as two years. During the first 6 months of nursing they will gain one-half to three-quarters of
a pound per day from the milk composed of colostrum (containing the mother's passive antibodies to protect
the newborn from early infection) and 40% fat. Nursing is done while swimming.
In this photo, the calf is readying itself for nursing
by placing itself in the "nursing" position (underneath the mother). It inserts its rostrum into one of the two mammary
folds on the mother's ventral side, forms a water-tight "straw" shape with its fringed tongue, places this straw onto one
of the two mammary glands, and then the mother squirts milk into the calf's mouth.
The fact that during nursing the mother
controls the transfer of milk to the calf (versus the calf suckling) is a great advantage for underwater feeding.
In this way, milk is not wasted and the length of time it takes the calf to nurse is kept to a minimum so that, in the wild,
the mother may maintain a vigilant watch for predators.
Solid food is usually not taken until the calf is 4-6 months old and about 50-60 inches in length, although male calves appear, in general, to
accept solid food at an earlier age than do female calves. The time at which a calf begins taking solid food is highly
dependent upon the individual. This solid food is consumed as a supplement to nursing.
Typically,
females will calve every 3-5 years, as the young nurse for up to 24 months and will remain with their mother up to five years.
During this time it would be very difficult for a cow to both mother a young calf as well as prepare for the birth of another. Female dolphins do not have reproductive senescence; in other words, they can continue to calve
throughout their life.
There is evidence to suggest that once a calf leaves its mother (at
about 3-5 years of age), should it again come in contact with her, each dolphin will recognize the fact that they have “met”
before, but will not recognize a familial relationship. Consequently, there is a chance that breeding between close relatives
could occur. But the oceans, being vast bodies of water, reduce the chance of this reunion.
A
newborn calf will take some time to get comfortable with the location of its blowhole and the breathing process. The complex
network of nerves surrounding the blowhole has not yet developed well enough to help it know when it has surfaced. For some
time following birth it will breathe by "chin slapping", or raising its head above the water higher than required to take
a breath. Also, a mother will often be required to steer her newborn calf away from obstacles until its echolocation
system has had a chance to develop and become functional.
Site Content
Understanddolphins.com contains information condensed from a number of reputable technical sources,
peer reviewed journal articles, and respected dolphin research facilities, as well as from my personal experiences and
observations as a dolphin VIP Tour Guide and Educator.
I have made every attempt to support the information presented in this site with video and still
photographic images. On a regular basis I plan to produce more of these images and will continue to update the site with these
as well as with any new and scientifically verified information which becomes available.
