Social Behaviour of the Bottlenose Dolphin
Frequent interaction with humans has led to the Bottlenose Dolphin becoming the most commonly recognised dolphin species, as well as one of the most well-known species of marine mammals. With proven intelligence, and a permanent “smile” on their faces giving them a friendly appearance, they are often the chosen favourite for many people when thinking of marine mammals.
Bottlenose Dolphins are extremely sociable animals and will often live in groups called pods. These pods are essential in providing hunting and mating opportunities for individuals, as well as providing security in numbers. The most common type of pod is a nursery pod, made up of up to 20 females and calves. Mothers form strong bonds with their calves, and so calves will stay with their nursery pod for several years before moving to a different pod. Juvenile pods are made up of young male and female dolphins that have left the nursery pod and united with other young dolphins. However, these juveniles will occasionally return to the nursery group containing their mothers for certain periods of time before moving back to their juvenile groups. Young female dolphins often return to their original nursery pods once mature, and will raise their calves with their relatives. Male dolphins are not often found within nursery groups. Male pods are slightly different to nursery pods and juvenile pods. Male
dolphins remain in juvenile pods longer than females as they take longer to mature. Once mature, male dolphins will bond with another male, forming a “pair-bond”. Unlike males in most other species of organisms that will compete with each other over females and territory, male dolphins cooperate to ensure a better chance of successful mating. The bonds between these males are very strong and pairs can remain together for over 20 years. These pairs can form alliances with other males to increase potential mating opportunities. In areas where food is abundant many pods amalgamate into superpods that may contain as many as 1,000 individuals. These superpods may contain more than one dolphin species.
While there is no rigid social hierarchy, bottlenose dolphins can be very aggressive, and members of a pod will try to establish dominance over others in a variety of ways. These can include biting and chasing other members of the pod, and repeatedly slapping the surface of the water with tail fins. The structure of a pod is fluid. Nothing binds individual dolphins to specific pods, many dolphins will frequently move between pods and some may only stay for a few hours before moving on. However, the individual dolphins present within a pod depend on a variety of factors, such as family ties, age, sex, etc. within each pod males are often the most dominant and it is believed that they do not form strong social bonds with females. Groups of males will often herd females to provide an increased chance of mating opportunities.
Communication between bottlenose dolphins is complex, consisting of both acoustic and non-acoustic forms. Dolphins can produce two types of sounds, pure sounds and pulsed sounds. Pure sounds, taking the form of whistles and chirps, known as frequency modulated sounds, meaning the pitch of these sounds changes over time. Pulsed sounds are made up of clicks. These clicks are used for echolocation but are also thought to be used for communication. Dolphins individually have a unique signature whistle to identify themselves to other dolphins within the pod. Dolphins have very good eyesight both in and out of the water and will use touch and body language to communicate as well as verbal sounds. Examples of this include (the aforementioned) tail slapping on the surface of the water to show aggression.
Despite the aggressive, dominating behaviours exhibited by bottlenose dolphins, individuals will regularly play with each other, carrying out activities such as passing items back and forth and chasing one another. Dolphins will also have regular body contact with other individuals, involving petting, rubbing and hitting each other. Individual dolphins will also remember the signature whistles of other dolphins, recognising friends and rivals. Dolphins can remember signature whistles for very long periods of time, sometimes for periods of up to 20 years. Males will patrol the outer areas of the pod to protect against potential predators. When encountering predators such as sharks, dolphins have three major responses, Tolerance, avoidance and
aggression. Most predators learn to avoid dolphin pods and sharks can remain in the same area as dolphins without any problems. The most common response is to merely tolerate them, or avoid them. However, when aggression is the necessary course of action, dolphins will work together to kill or dissuade any potential predator, using superior numbers and teamwork to their advantage. Dolphins do not only socialise with other dolphins however. They are incredibly curious and will often interact with people if provided with the chance.