Bottlenose Dolphins
(Tursiops truncatus)

Females have one calf at a time. The inter-birth interval is at least 4 years, time enough for one calf to become independent of its mother before another is produced. Males are not involved in parental care and are generally not attracted to females when they are accompanied by offspring under 2.5 years, which is when calves are most dependent (Connor et al., 1996).

The core unit or group in a herd is a mother and her calf. This pair forms incredibly strong bonds and is nearly inseparable for 2.5 years. This strong bond is essential for calf survival, as offspring are completely dependent on their mothers for food, locomotion and protection. Though calves are born precocial (they can swim right away) their muscle development is poor so travel is difficult. Thus, newborns assume an "echelon" swimming position in contact with the mother, at her side, riding on the current produced by her movement (Gubbins et al., 1999). After 2-4 weeks, muscle and motor coordination are more developed, so the calf can move to the "infant" position, swimming underneath the mother, to enhance quick access to her mammary glands, as calves must feed every 20 minutes (Gubbins et al., 1999).

As the calf gets older, its physiological and social development progress slowly. Offspring incrementally gain independence from their mother, moving further away from her, spending less time with her, and more time socialising with other juveniles. At about 4 years, juveniles are proficient enough in their strategies for hunting, predator avoidance and courtship to leave the mother’s side. Juveniles (especially males) then join a juvenile herd, but return occasionally to the natal herd (Gubbins et al., 1999)..

Allomaternal care
In the first week of a calf’s life, inexperienced, non-parous females will try to steal the calf away from its mother, but the latter quickly retrieves her offspring and displays threat behaviours towards the kidnappers (Mann and Smuts, 1998). This first week of life is thought to be essential for the calf to recognise its mother. During this first week, the mother whistles almost continuously and is in permanent physical contact with her calf, so her calf not only imprints on her vocally, but also visually, recognising her signature whistle and her body colouration, pattern, and distinguishing marks or scars (Mann and Smuts, 1998).

By the second week, mothers allow other females in their herd to escort their calf. These females are likely to be sisters or aunts of the calf, or they may be unrelated (too few studies to determine). Inexperienced or young females are more likely to escort calves than are older, previously parous females, implying that this babysitting behaviour offers training and experiential advantages for dolphins that have yet to care for their own offspring. Furthermore, females that have been exposed to alloparenting situations, consistently exhibit higher survival rates of their offspring (Mann and Smuts, 1998).