-- MAIN LINKS --
-- EVOLUTION
& ADAPTATION -- BALEEN WHALE SPECIES
--
-- CLASSIFICATION -- CHARACTERISTICS
OF BALEEN WHALES --
-- TOOTHED WHALE SPECIES -- DOLPHINS
-- SEALS --
-- ENDANGERED SPECIES
-- THREATS
-- GAMES --
-- DOLPHINS
--
. Anatomy
. Senses . Feeding
. Behaviour . Reproduction
.
. Communication . Marine
ecosystem . Dolphines on display
. Training .
DOLPHINS: Behaviour
---Background
People have always been fascinated by dolphins playing in the bow-waves and wakes of ships. Seemingly, dolphins have no fear of people and readily interact with ships, divers and swimmers. On occasion, people have been saved from drowning by dolphins, who have pushed them towards a beach. Stories like this have been told for centuries and are still being told.
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The bottlenose dolphin, the best known dolphin species, is a social animal. They live in small groups and sometimes in larger schools. They hunt together and sometimes share the responsibilities of raising the young. This social behaviour is probably the key to the survival of many dolphin species. To better understand the behaviour of dolphins in general, an understanding of the dynamics of living in groups is necessary.
---Group composition
The smallest social unit of dolphins is a pod. In the bottlenose dolphins, pods are subject to change, although some units can remain the same for long periods of time. In the Florida dolphin populations, there are several types of groups:
*mother-calf pairs
* mixed-sex groups of subadults
* single-sex groups of subadults (all male or all female groups)
* bands of females with their most recent offspring
* adult male groups (usually strongly bonded pairs or trios of adult males).
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Often, pods change size and composition depending on the activity: social travelling pods are usually the largest, while feeding pods are usually rather small.
Group composition may very per geographical region and per species. In killer whales for instance, the pods are matri-linear groups, meaning that all members of the pod are related through the alpha female. In the Florida coastal waters, bottlenose dolphin groups usually consists of 2-10 individuals. In other areas (for instance in the Gulf of California) pods are larger (on average 15 animals).
Group size seems to be influenced by environmental factors such as geography of the area and food availability. In the deeper, offshore waters, the groups are usually larger and can consist of more than 100 individuals. Larger groups of animals are usually referred to as herds. Occasionally, herds can consist of individuals of different species.
---Group behaviour
The following is based mainly on studies done in Sarasota Bay, Florida.
The bond between mothers and their calves is strong. Calves stay with their mothers for a long time, usually 3 to 6 years, but sometimes even longer. Even later in life, dolphins occasionally associate with their mothers, although usually only briefly. When the calves leave they join subadult groups. These groups are rather stable. These subadult groups are quite active. The dolphins are often seen jumping, chasing and socializing. Socializing involves a lot of physical contact, including rubbing, stroking and pushing, as well as both hetero- and homo-sexual interactions. In these groups the young dolphins learn how to behave in a group and also a hierarchy will be established.
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Bands of females are fluid: females in a band often interact with each other, but usually do not stay together for long periods of time. Often, females in the same reproductive condition will group together: females that are pregnant, or females with calves of approximately the same age. Once a female becomes pregnant she may leave the band she usually associates with and join a band of pregnant females.
Adult males rarely associate with subadult males. Adult males may stay solitary, but often two or three males form a tight bond. Such a bond may develop when the animals are still subadults and it may persist for a long time. These male pairs and trios often work together in aggressive encounters towards other males. Also, these males may together try to separate a female from a group for mating purposes.
While feeding, the dolphins are usually spaced far apart
and there does not seem to be a lot of co-operation in the Florida dolphins.
In other areas, dolphins do often work together. One of the most
spectacular examples is found in dolphins in the Mississippi delta, who
as a group chase a school of fish onto the river bank and then follow
the fish onto the bank and grab the fish out of the water.
When dolphins are travelling, their movements are usually synchronized: they dive together and they come up to the surface to breathe together.
Dolphins can be active both night and day. A large part of their activity pattern is dictated by the food they eat. In some areas, their prey stays deep during the day and comes closer to the surface during the night. In those areas, dolphins are more active at night and rest more during the day, when no food is available.
On average, dolphins sleep about 30% of the day. Their
sleeping behaviour is different
from our own. When people sleep, the whole brain displays a sleeping pattern.
In dolphins, only
one half of the brain sleeps at any given time. The brain hemispheres
take turns in sleeping. The REM sleep phase, which in humans is associated
with dreaming, is probably totally missing in dolphins. If this means
that dolphins do not dream is hard to say, though.
For more information about reproductive behaviour, see the reproduction section. For more information about communication see the communication section.
---Playful behaviour
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Dolphins are often seen frolicking in the bow waves and
wakes of ships. In this way dolphins can move faster than they could on
their own. They are pushed forward by the waves and save energy
while travelling. Occasionally, dolphins have been seen riding the bow
wave of large whales as well. Dolphins learn to do this very early in
life: a calf also positions itself relative to its mother so that it rides
the bow wave of the mother. In this way, the small calf can keep up with
its mother without spending a lot of energy.
Dolphins can jump clear of the water and they often do this for no apparent reason. When travelling at high speed, dolphins sometimes make low jumps to save energy. This low jumping behaviour is often called porpoising. Jumping can also have a signalling function. In that case the dolphin jumps up and falls back on the water on its side, making a lot splash. This is called breaching and can be heard over long distances. Some dolphin species, like the spinner dolphin, are known for their complicated high jumps. In oceanaria, dolphins are often trained to perform these complicated jumps on cue. It is fascinating to watch and it demonstrates the power of the dolphins. An experienced trained dolphin can jump up to 5 m. clear of the water.
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Dolphins have been seen playing with a variety of objects. These can be inanimate objects such as mangrove pods, leaves or feathers, but also living animals, such as turtles, sea gulls and jelly fish. In the Sado estuary in Portugal, dolphins often kick jelly fish around with flicks of their powerful tails. Sometimes dolphins also blow bubbles under water and play with the bubbles or bubble rings.
---Care-giving and co-operative behaviour
There are many stories of dolphins supporting a sick or
injured member of the group. However, this has not been observed very
often. Recently, a group of dolphins has been observed swimming
away from another dolphin that was entangled in a fishing net.
Dolphins have been seen to co-operate in chasing off other dolphins that were harassing a group member or trying to keep a shark at bay. When resting, usually a few group members (positioned on the edge of the group) take on the role of guards, so that the others can rest comfortably.
---Interactions with other species
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Bottlenose dolphins have been seen together with a number of other dolphin species as well as larger whales. Conversely, some fish species seek out dolphins and stay close to them, grabbing pieces of food that the dolphins spill. The best known of these is the remora.
---Pantropical spotted dolphins
In the Bahamas, bottlenose dolphins are often seen together with spotted dolphins. Sometimes, the interactions are aggressive, but sometimes groups of bottlenose dolphins help spotted dolphins separating females from a group and thus participate in the spotted dolphins' mating.
In other areas, the interactions are not very friendly. In Scotland, groups of bottlenose dolphins have been seen harassing and even killing harbour porpoises.
In a number of places, bottlenose dolphins have been interacting with people. In many cases, these were solitary animals, seeking out the company of humans. One of the best known is Fungy, in Dingle Bay, Ireland. There is also a so-called sociable dolphin near Karmøy in Norway (the locals call him Flipper). There are also groups of dolphins that participate in fishing activities, for instance in Mauretania. There the dolphins chase the fish into the fishermen's nets and can then also get some fish in an easy manner themselves.
---What do we know about wild dolphins?
For quite some time it has been very difficult to study the behaviour of dolphins in the wild. Since these animals spend most of their time under water, following them and seeing what they are doing is hard. Also, these animals are relatively long lived and consequently their development is slow. Discovering trends and behaviour patterns takes a lot of time and patience.
Currently, only a few populations have been studied long enough to get some idea of the group composition and group dynamics. These are the bottlenose dolphin population in Sarasota Bay, Florida and the spotted dolphins (which interact with bottlenose dolphins) in the Bahamas. A number of other studies are currently under way. In these studies, individual dolphins are identified using photographs of unique markings on their bodies, in particular on their dorsal fins.
When you can recognize individual dolphins, it becomes possible to see who associates with whom and also to get some data on vital statistics, such as survival rates. In a number of cases, the techniques now used in the field have been developed, tested and refined in laboratories and oceanaria. By combining the results of both captive and field studies, it becomes possible to get a comprehensive picture of dolphin behaviour and physiology.
| In finnish |