Female bottlenose dolphins reach sexual maturity between 5-13 years old and can give birth as old as 45 years old. Breeding can occur year-round and seasonal calving varies by area.

A calf's gestation period is 12 months long. They are born under water, either tail- or head-first. The umbilical cord snaps during or after the delivery.
To see a video of a birth, go here: http://www.seaworld.org/animal-info/video-library/commerson.mov

Calves nurse for 12-18 months and stay with the mother for 3-6 years. Calving occurs every 3-6 years.

YouTube: Two Aquarium Dolphins To Give Birth
http://www.youtube.com/watch?v=HWYxwsqcYgw

YouTube: Dolphin Birth
http://www.youtube.com/watch?v=uWozgwTbIn4
Source(s):
http://www.seaworld.org/infobooks/Bottlenose/birthdol.html
http://animals.nationalgeographic.com/animals/mammals/bottlenose-dolphin.ht...
http://www.acsonline.org/factpack/btlnose.htm
http://www.nmfs.noaa.gov/pr/species/mammals/cetaceans/bottlenosedolphin.htm
http://www.seaworld.org/animal-info/video-library/commerson.mov

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