Bottlenose Dolphins
(Tursiops truncatus)

Dolphin populations can be divided into several social groups depending on the size and duration of their associations. School/pod sizes very depending on habitat, with more protected habitats (like Florida) harbouring fewer dolphins, while more open, deeper areas support larger pods (Moller and Harcourt, 1998).

Herd
"A natural congregation of dolphins that uses a certain home range, has prolonged independentexistence, exhibits interrelated behaviour among individuals, and apparently shares a kin relationship" (Bel’kovich et al., 1991, p.18). Herds generally consist of adult females and their offspring, since males are solitary or found in pairs.

Photo credit: www.aqua.org 

Group
"Designates smaller units within the herd; groups are constituent parts of the herd and cannot exist without the herd over a long period" (Bel’kovich et al., 1991, p.18). The basic group unit of the bottlenose dolphin is the mother and her calf. If she has several older juveniles, these may also be part of a group or a herd. Adult males are solitary, but they may form into pair groups or cohorts with another male (Moller and Harcourt, 1998). Juvenile "play" groups also form, which may be where males establish their close association with another male.

Photo credit: www.aqua.org

School/Pod
"An unstable association of several herds" (Bel’kovich et al., 1991, p. 18). Schools are very fluid, with different herds intermingling temporarily to hunt or socialise. Temporary mating schools which include males may form. In addition, several groups of males may form temporary associations in order to herd oestrous females for mating. Breeding schools, or cohorts, consisting of females in oestrous, may also form (Connor et al., 1996). These breeding schools facilitate the identification and herding of oestrus females by males. Moreover, these cohorts keep aggressive males away from pregnant females, or females with offspring.