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When fully grown this dolphin will only need to breathe 2 to 3 times per minute. Humans are involuntary breathers, meaning we continue to breathe even if we’re unconscious. But dolphins are voluntary breathers. They must make a conscious decision to inhale air. Unconscious dolphins die from asphyxiation.
This means that dolphins never truly sleep in their whole lives. Their brain must always be active enough to initiate breathing.
Clip from the documentary “Animals in the Womb”.
Watch it here – https://youtu.be/XaZW7bbmc9I