How does reproduction in dolphins work?
Dolphins’ reproductive organs are located inside the body, with genital slits on the ventral (belly) side. Males have two slits, one for the penis and one further behind for the anus. Females have one genital slit, housing the vagina and the anus, with a mammary slit on either side.
Dolphins are polygamous, meaning they have more than one mate. There is no actual mating season for dolphins. They can mate throughout the whole year. Ninety percent of their mating activity, however, is foreplay. On the other hand, intercourse only takes seconds (Wells et al ,1999).
The age of sexual maturity varies by species and gender, but in general males become sexually mature between 8 to 14 years of age and females become sexually mature a little sooner; around 5 to 13 years of age (Orbach, D et al 2019).
Male dolphins often appear to coerce females into sex, and it can be hard to tell what a female really wants in a mating situation (Scott et al, 2005). Sometimes in our tours we can see lots of males harassing a single female.
What about the baby dolphins?
Depending on the species, dolphins are pregnant between eleven and seventeen months. Calves are usually born tail first. We can get an approximate idea of how old a baby is by looking at the dorsal fin. It is thought that the dorsal fin stiffens within a few hours. The tail flukes seem to take a bit longer. Also, when babies are born they have lighter colored bands spanning their midsection. These are called fetal bands and are caused from being scrunched up in the mother’s womb. These bands will slough off after multiple weeks (Wells 1999).
A baby dolphin swims in a position next to its mother called the echelon position. The baby swims in this position to catch mom’s slipstream, allowing the calf to work less hard in order to keep up with its mother. They nurse, on average, a minimum of one or two years, but have been observed nursing up to four and a half years (Wells 1999).
Dolphins with calves produce milk in their mammary glands. The milk is very high in fat and contains colostrum. Colostrum provides antibodies that help protect the calf against infection during those critical first months of life (Eichelberger, L et al 1940).
Dolphins communicate through the emission and reception of sounds. Each dolphin develops its distinctive sound within the first years of life. All individuals produce a unique sound, which is different to the others so they can identify each other, it is like us humans with our names. On our trips you can listen to their sounds quite often!
But, also dolphins use different behaviour or body language to communicate among each other. In almost all of our tours we can observe some of this dolphin communication, like the following:
Identification of body colouring patterns.
Stains, stripes, and specks may indicate the health status or the age of dolphins’ companions. For example, the skin of the Atlantic spotted dolphin (Stenella frontalis), whom arrive to the Azores in the summertime, develop spots when they grow older, and the scars in the skin of the Risso dolphin, one of our resident species, (Grampus griseus) informs others of their combat skills and experience.
The body positions sometimes can demonstrate anger or aggression in dolphins. For example, what is called the S-posture normally is used in two specific social contexts: courtship and aggression. Males dolphins fight with one another for many reasons, including over resources such as food, space, females, or to establish societal dominance or rank (Waal & Harcourt, 1992).
The skin of these cetaceans is very sensitive to the touch. If they are in a good mood, then they can make physical contact with the flippers by pressing them against the flippers of another dolphin (Azevedo, A et al 2010).
Tail Slapping and Flipper Slapping
It is a vertical blow of the tail or the flipper against the water surface that sometimes indicates aggressiveness, but it can also express the desire to leave the area where they are, or ask for attention of the other dolphins (Azevedo, A et al 2010; Herzing, 2000).
Perhaps this is the most common behaviour that our tourist can see in our tours. Dolphins approach our bow and are propelled by the vessel’s waves. Dolphins have learned to harness this “free” energy and take advantage of the opportunity to rest. And at the same time they are having a moment of fun.
Finally, Among the all the different types of behaviour, we finish with the jumps.
Why do the dolphins jump?
Everybody knows dolphins jump. We are used to see dolphins jumping in zoos or aquariums, but unfortunately in those situations they are being forced to jump in exchange of food. On the other hand, in nature, dolphins jump whenever they want and for many reasons. Let’s explain some of them.
For example when dolphins are travelling at high speed they are forced to stay close to the surface in order to maintain respiration for the energetic exercise, that it’s called porpoising and occurs mainly when dolphins are swimming at speeds greater than 4.6 m/s. (Weihs,D 2002)
Sometimes we see a group of juvenile dolphins very excited and jumping to communicate to each other Aerial and percussive behaviour are more spectacular and easier to record, and they have therefore attracted most of the research and tourists attention. They seem to be more often observed during feeding bouts (Acevedo-Gutierrez, 1999).
Some studies have shown that Hawaiian spinner dolphins (Stenella longirostris) proposed that aerial behaviours were used socially to reafﬁrm social bounds before a hunt. (Norris and Dohl, 1980) On the other hand, others studies proposed that Argentinean dusky dolphins (Lagenorhynchus obscurus) use jumps more directly to herd schools of prey at the surface for easier capture. (Würsig ,1980). These hypotheses are not mutually exclusive but they cannot apply to all situations (e.g. some dolphin species do not hunt cooperatively or hunt schooling ﬁsh at the surface).
Sometimes in our trips we can observe feeding moments with a lot of jumps, splash and tail slapping.
Removing external parasites, it’s another reason why dolphins jump. They may jump to shed parasites they have picked up. A lot of times we can see when a dolphin jumps into the air and spins, and remoras flail out.
The most acrobatic dolphin is the spinner dolphin. Just in one astounding leap into the air, they can spin around up to seven times. With underwater movie footage and a mathematical model, scientists from West Chester University can now explain how dolphins manage the acrobatic feat. Unfortunately, the Azores isn’t in their distribution habitat, they are most commonly around Hawaii and Mexico.
So, as you can see exists all kinds of reasons for dolphins jump naturally in the wild: to display dominance, to communicate their location, to call each other, to hunt, to take off parasites… or sometimes simply just for fun!
Now, you are almost expert in dolphins …what about to join us on a trip to see these facts “in situ” of these incredible cetaceans on their habitat. We wait for you!
Written by Maria Huaman
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