Nature trail

Dolphins:

Intelligent mammals

Most of you would have been very fascinated with the pink river dolphins we featured a couple of weeks ago, on Nature trail. They really are cute freshwater mammals with seemingly smiling faces, and are recorded to have a close relationship with humans.

Today, we’ll surf the oceans to learn about their cousins, the marine mammals who also belong to the Delphinidae family.

Believed by many a scientist to have evolved around 10 million years ago (in the least), dolphins are considered to be one of the most intelligent animals on Earth today. There are about 40 species of dolphins, including the five freshwater dolphins found worldwide, especially in shallow seas of continental shelves.

The name dolphin is believed to have originated from the Greek word delphis and then undergone many changes when translated to Latin (delphinus) and Old French (daulphin), to what it is today.

Did you know that of the 40 species in the family of dolphins, six species are commonly known as whales even though they are strictly dolphins? So, don’t be confused if you are told by someone that the famous killer whale or orca named Willy, about whom even the famous pop star Michael Jackson sang is not really a whale but a dolphin.

The other five species that are called whales and sometimes known as blackfish are the Melon headed whale, Pygmy killer whale, Long finned pilot whale, Short finned pilot whale and the False killer whale.

Now, let’s check out the appearance of these friendly marine mammals who are mistakenly called ‘fish’ by some, since they live in the sea. Just as much as bats are not birds even though they fly, dolphins and whales too are not fish, but mammals that live in the sea (or we could say water, as there are freshwater dolphins too).

Some of you may be already familiar with what a dolphin looks like. It has a streamlined, ‘fusiform’ body which is specially adapted to fast swimming. If you have noticed a tall fin on the top of its body and wondered what purpose it serves, here’s the answer.

This fin which is called the ‘fluke’ is used for propulsion. The pectoral fins or flippers, together with the tail section provide directional control. These flippers are also used to stroke one another, especially when playing. The dorsal fin (not all dolphins have this) provides stability while swimming.

The basic colour pattern is shades of grey, but it varies with the species like in the case of the freshwater dolphins which are pink hued.

Generally the underside is paler than the top part. Often the dolphin sports lines or patches of different hues which contrast with the rest of the skin. It also varies in size from 1.2 m (4 ft) and 40 kg up to 9.5 m (30 ft) and 10 tonnes! Yes, the orca is really big compared to some small dolphins like the mauis dolphin.

The dolphin has very good eyesight both in and out of water. Its sense of hearing is said to be superior to that of humans. It has small ear openings on either side of its head. It is also said that the lower jaw bone plays a role in helping the dolphin to hear underwater.

Scientists believe that sound vibrations are conducted to the middle ear via a fat-filled cavity in the lower jaw bone. The dolphin also uses its hearing ability for echolocation. Scientists also say that the dolphin’s teeth are set in a way that works as an array or antenna to receive incoming movement.

A dolphin’s sense of touch too is well developed, however it lacks olfactory nerves and lobes. So, scientists believe it does not have a sense of smell!

Some of you may be aware that a baby dolphin is called a calf. Female dolphins give birth to a single calf after a gestation (pregnancy) period of nearly one year or more, depending on the species.

Small dolphins such as the tucuxi give birth after 11 or 12 months while the large dolphins like the orca give birth to a calf after about 17 months. The baby suckles from the mother up to about four years. It usually stays with the mother for about three to six years, learning feeding techniques, social interaction and group foraging.

Scientists say that dolphins show cultural behaviour, something long believed to be unique to humans. They have observed some dolphins in Australia (Indo-Pacific Bottlenose dolphins) teaching their young to use tools.

These dolphins are usually in the habit of breaking sponges off from surfaces to cover their snouts when foraging for food. Scientists have noticed them teaching this to their female offspring.

How do these gentle mammals communicate? It is said that they have a range of sounds which they make using nasal airsacs just below the blowhole.

Some species of dolphins are capable of sending identity information to each other using a single whistle. The dolphins echolocation clicks are said to be among the loudest sounds made by an animal in the sea.

You may be surprised to learn that the dolphin, despite its gentle appearance is carnivorous. Its diet consists of fish and squid mainly. However, killer whales and false killer whales eat other marine mammals. The killer whale (orca) is known to capture sea lions on the beach and also prey on smaller dolphins at times. However, this happens very rarely.

The Earth’s most intelligent water - dwelling mammals, the dolphins are social animals and generally live in pods (also called schools) which comprise a dozen or more individuals.

In places where food is found in plenty, these small pods mingle together and temporarily form what’s known as super pods, which could exceed a thousand dolphins.

Membership in pods is not very rigid, but dolphins are known to establish strong bonds with the members of their pod. They are known to stay with ill or injured dolphins in their pods and actively help them breathe by regularly bringing them up to the surface, if needed.

Do you know that a dolphin breathes through a blowhole that’s located on the top of its head? It can empty and refil its lungs in less than a fifth of a second. It cannot breathe underwater since water can get into the blowhole and it can drown. So, how do you think it knows when exactly to open the blowhole to take in air?

With the help of complex nerve endings around the blowhole which senses pressure changes. This helps the dolphin to know when the blowhole is in or near air to open it. Powerful muscels around it closes the blowhole as it dives into the water after coming up for air. Now you can understand why dolphins help injured or ailing dolphins to come up for air.

Don’t you think this is an admirable quality among these sea creatures? Sometimes this type of unity and commitment is lacking even in human beings, so it is really fascinating to note that dolphins will go to such extremes to help one another in times of trouble. What’s even more fascinating is that these aquatics do not limit this type of behaviour to their own kind.

They are famous for helping even humans, who are unfortunately one of their prime natural enemies. Even you may have read or heard of incidents where dolphins have come to the rescue of many troubled humans such as swimmers, divers and even those whose boats or other modes of sea transport have capsized.

For instance, if a diver or swimmer is threatened by sharks, these gentle mammals are known to come to their rescue by either forming a circle around the humans and allowing them to swim to safety or by guiding them to safety when drowning. So, let’s protect them whenever we can, like they protect us when they can.

Facts and pix: Internet

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Fact file

Dolphins, porpoises and whales are said to be descendants of terrestrial mammals.

Ancestors of the modern-day dolphins are believed to have entered the water about 50 million years ago.

Apart from the 40 recognised species of dolphins there are hybrids. (false killer whales crossed with bottle nose dolphins), known as wolphins. Among the 40 species of dolphins are Irrawaddy dolphin, Atlantic spotted dolphin, Chinese white dolphin, Bottlenose dolphin, Indo-Pacific bottlenose dolphin, Northern rightwhale dolphin, Southern rightwhale dolphin, killer whale, tucuxi and costero.

As dolphins are mammals and not fish, they are warm blooded like humans.

Dolphins don’t sleep the way other land mammals do as they have the need to come up regularly to breathe and keep eyes open for danger. They have to maintain some amount of consciousness all the time. So, they sleep with one brain hemisphere at a time, in a slow wane sleep.

Dolphins occasionally leap above the surface of the water and are also seen performing acrobatic movements, but no one knows why they do so.

As a dolphin breathes, air leaves the blowhole at speeds of over 100 miles per hour.

Bottlenose dolphins can dive to depths of over 1,640 ft (500m).

Play forms an important part of their lives and dolphins could be seen playing with seaweed, play fighting with other dolphins and riding the waves.

Most small species of dolphins are attacked by larger species of shark such as the tiger shark, great white shark, dusky shark and bull shark.

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