|Dolphins > Breeding|
Cetaceans are mainly social animals, they are not solitary but spend all of their lives together in groups of varying numbers ranging from a family of three to many hundreds. Because the oceans are so bountiful, the cetacean population was very large. Unfortunately today, the situation is rather different. Modern methods of hunting have decimated some species to the point of virtual extinction, as in the case of the Baleen Whales. Even if all whale hunting was stopped now, it would take over a hundred years for some members of the mysticeti to significantly increase their numbers. Once a population drops below a certain figure the chances of finding a mate are significantly reduced, this is doubly so for Cetaceans who live in the immensity of the oceans. Cetaceans are slow breeders, only producing one offspring at a time, usually every other year and even the shortest lived do not start breeding until they are about five years old.
In order to reproduce, mammals have to mate. In order to mate, they have to find a partner who is receptive or can be induced to become so. This can be quite a problem when they live in an environment in which they cannot see very far, or their nearest neighbour may be 150 miles away. We said earlier that cetaceans travel in groups. They do, but a particular group of Baleen Whales could be spread over an area of several hundred square miles. The only method of communication between them is sound.
We have discussed the incredible hearing of these creatures before and now it is perhaps time to go into some aspects of their speech. Cetaceans produce sounds by passing air through various passageways in the head, but unlike other animals, for reasons that may now be apparent to you, do not actually expel air when they are vocalising. The air is only being transferred from one cavity to another within the head and it is though that the prominent bulge displayed on the forehead of some species, acts as a lens concentrating the sound waves into a beam. These 20-Hz low frequency sounds can be heard over hundreds of miles between some of the mysticeti and are the only means of communication between them.
Some of you may have heard a ballad that was often played on the radio a few years ago which featured the song of the Humpback Whale. It had a lovely haunting real whale accompaniment. What in fact you were listening to was the mating call of this animal. It is a very peculiar fact, but the song of the Humpback Whale may last as long as 30 minutes without any repetition of the words at all. During a period of several weeks the singing, which may last for twenty four hours at a time, is gradually changed, each whale composing his own special version.
Once having found a suitable mate, the male cetacean puts on a display of diving and leaping that has to be seen to be believed. Right alongside the boat, we have seen Pilot Whales leaping as high as 12-15 ft out of the water during such a display. The object seems to be to make the biggest splash possible, the sound carrying a great distance underwater as the impact is in the region of 2 tons. Eventually the female joins in, the two quite literally making high speed passes at each other. Gradually they come into physical contact, swimming belly to belly, sometimes with their flippers around each other, this still being part of the courtship. The actual method of mating varies from species to species, some couples remaining stationary in the water in a vertical position whilst others are horizontal. In some cases they may involve a very close friend on the other side of the female to keep her pushed against the male!
The reproductive organs of cetaceans are not visible externally, but for better streamlining are kept within slits in the body; the male's some distance from the vent, the female's in close proximity. In her case the two mammaries are also enclosed, and are in the same area. Coition lasts for about 30 seconds, which may not seem very long, but the cetacean is a very sexually active animal and may mate a dozen times a day. It is also interesting to note that this high level of sexuality is unusual in animals apart from man. We are afraid to say that in the case of the Common Dolphins they are not too selective in choosing an object for their sexual gratification. We have seen males chasing males and other immature dolphins. The male dolphin is able to indulge in this high level of sexual activity, as he has a muscular erected penis which he can erect at will.
In the film "Ride a Wild Dolphin" shown by Yorkshire TV there is a lovely episode, where Maura Mitchell is approached by Donald the Dolphin who appears to be sexually aroused. One cannot say whether he was attracted by her femininity or because he wanted to examine the texture of her wetsuit in the only way he could. However ladies, if you are ever approached by a friendly dolphin whilst swimming, please remember that they are classed as Royal Fish and belong to the Crown. Complaints to Buck House please!
The gestation period of cetaceans varies between 10 and 16 months. This is quite a short time for what can be a very large animal and the foetus has to develop very rapidly. It also has to be remembered that the new born baby is being born into a very hostile environment and has to be completely formed and ready to swim alongside his mother immediately. The trauma of being born is quite a shock to all warm blooded animals and this must be doubly so for the cetacean, who after emerging from the warm birth canal, finds that he is in very cold surroundings and cannot breathe.
Cetacean births are usually breach presented to enable the baby to stay inside the mother for as long as possible until the process is completed. In some cases, upon separation, the mother is assisted by other females who have been in attendance during the birth, one or more of which will help to bring the newborn baby to the surface and start it breathing. When this is achieved and the mother is sufficiently recovered, she takes over and starts suckling her offspring. The baby at the time of birth is about a quarter to a third of its mother's length.
Cetacean milk is some of the richest in the animal world, comprising up to 40% fat content. The mother feeds her offspring by erecting a nipple from within the mammary fold and injecting the milk under high pressure into the baby's mouth, enabling it to receive large quantities in between coming up to the surface to breathe.
The Bay of Gibraltar seems to be a favourite place for nursery schools of Common Dolphin and on one occasion we witnessed the birth of a dolphin in the wild. It is a very common sight to see baby dolphins accompanied by their mothers who always stay very close to them, rising to the surface a few inches away from each other when coming up to breathe. From our observations in the Bay of Gibraltar, there does not seem to be a set season for giving birth because young of only a few days old are present throughout the year.
Lactation lasts for about 12 months, after which the weaning process is started. In the case of the Odontoceti, the mother bites off the head of small fish and offers the carcass to the young animal. This technique is used in Dolphinaria to induce newly captured dolphins to feed, as they will generally not take dead fish but do have a childhood memory that such food was offered to them by their mothers. About five years later, a new generation of dolphins are starting to breed.