Female Reproduction

Our long-term study has revealed:

  • The months of October – December are the peak birth months, occuring just before the peak in surface water temperature. (Figure 1)
  • Females give birth to their first calf at ages 12-15. However, a few females, such as a dolphin named “Peglet”, have given birth to their first calves at the age of 11.
  • Interbirth intervals for surviving calves range between 3- 8 years. Interbirth intervals of 4 years were most typical. (Figure 5)
  • One third of all females studied have not calved successfully in a 10 year period. Reproductive success was defined as the number of calves surviving to 3 years old within a ten year period. (Figure 6)
Figure 1: Number of births and average temperature by month (SD ranges for temperature= 0.9-1.6). If a birth could not be assigned to one month, it was divided equally among the possible birth months. (N = 74 calves, 47 mothers).
Figure 5: Interbirth intervals when the first calf survived to weaning (N=33). The graph demonstrates that average birth interval is 4.55 years (SD=1.00, median= 4.07). Shaded bar represents a possible gap if she gave birth >1 year after weaning for first calf, then she could have lost a fetus in the interum.
Figure 6: Graph demonstrates 30% of the females had no surviving calves, 37.5% had one surviving calf, 25% had two surviving calves, and 7.5% had three (N=40).
Ewa Krzyszczyk

Results and figures taken from: Mann, J., Connor, R.C., Barre, L.M. & Heithaus, M.R. 2000. Female reproductive success in wild bottlenose dolphins (Tursiops sp.): Life history, habitat, provisioning, and group size effects. Behavioral Ecology, 11:210-219.