Dolphins are closely related to whales and porpoises and there are close to 40 species of dolphin. Most popular is possibly the bottlenose dolphin with its upturned mouth that makes it look like it is constantly smiling. While there have been cases where dolphins have rescued humans from drowning, dolphin research has also shown many cases where dolphins have shown aggression towards humans.
Dolphin Facts
There are around 32 species of ocean dolphin and about 5 species of river dolphin. Dolphins can range in size from 1.2m – 9.5m in length and weigh between 40kg – 10 tonnes. The killer whale (Orca) is actually a member of the dolphin family, as is the pilot whale. The killer whale is the largest member of the dolphin family and can reach lengths of 30 feet.
Dolphins are carnivores and feed mostly on fish and squid and will often compete with sharks for food. An adult dolphin can eat up to 30 pounds of fish in a day. If a shark chases or attacks a dolphin, the other dolphins of the pod will then attack the shark and attempt to drive it away.
In the wild the dolphin’s average lifespan is 17 years, but they can live for up to 50 years. Dolphin calves are born tail first, which is unique among mammals. The calf will stay with its mother for 2-3 years, but some dolphin-to-dolphin bonds last a lifetime. Current taxonomy of the dolphin is:
- Kingdom: Animalia
- Phylum: Chordata
- Class: Mammalia
- Order: Cetacea
- Family: Delphinidae
Genus and species will of course depend on the dolphin in question. For example there are two species of bottlenose dolphin; Tursiops truncates (common bottlenose dolphin) and Tursiops aduncus (Indo-Pacific bottlenose dolphin).
Dolphin Intelligence and Behaviour
Dolphin intelligence is quite simply due to the size of their brain. The dolphin’s brain is large for its body size, in fact it is larger then the brains of chimpanzees and great apes in relation to body size. It is second only to the human brain comparative to body size.
Dolphins are able to process acoustical information gathered during echolocation and are easily trained to perform in marine parks, however dolphin research tests show that dolphin intelligence is on par with elephant intelligence.
Dolphin Research and Aggression
Both myth and media, such as books, television and movies have promoted the good natures and friendliness towards humans of dolphins, and few point out their aggressive behaviours. The ancient Greeks believed that it was good luck to have a dolphin ride the waves at the bow of their ship, and shows like ‘Flipper” further spread the good PR about dolphins.
Dolphin research has in fact shown several instances of dolphins showing aggression towards humans. In a study of solitary dolphins that tended to seek out human company, only one dolphin of 29 behaved favorably by rescuing a drowning boy. Others kidnapped people, dragging then out to sea so they had to be rescued by boat, some were aggressive, butting, ramming and nudging people causing injuries such as fractured ribs and unconsciousness, while others displayed misdirected sexual advances towards people.
There have been some cases where tourists have been bitten by dolphins at Monkey Mia, a tourist spot in Western Australia where people stand in knee-deep water and feed dolphins. So while dolphins are intelligent, playful and very cute, it is important to remember that they are still wild animals and can be potentially friendly or aggressive towards people. And at 40kg to several tonnes in weight, the human is most likely to be at the losing end of that scuffle.
References: Animal Planet and Kruszelnicki, K, 2008, ‘Fraudulent Flipper’ in Science is Golden, ed. Harper Collins Publishers, Sydney, NSW.
Roberta Goli - Roberta has a Bachelor of Science Degree (Zoology), has worked with animals for over 10 years and enjoys writing short stories and flash ...
