In biology, a blowhole is the hole at the top of a Cetacean's head through which the animal breathes air. It is homologous with the nostril of other mammals. As whales reach the water surface to breathe, they will forcefully expel air through the blowhole. The exhale is released into the comparably lower-pressure, colder atmosphere, and any water vapor condenses. This is often visible from far away as a white splash, which can also be partially caused by water resting on top of the blowhole.

Sound production

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Air sacs just below the blowhole allow whales to produce sounds for communication and (for those species capable of it) echolocation. These air sacs are filled with air, which is then released again to produce sound in a similar fashion to releasing air from a balloon.

Evolution

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The evolution of the blowhole isn't entirely clear, but it is known that the early whales still had nostrils on the front of their head and that they moved to a position further back on their head over time, but still in front of their brain which has moved backwards as well. Baleen whales have two blowholes positioned in a V-shape while toothed whales have only one blowhole. The sperm whale is a toothed whale and also has a single blowhole, but unlike other toothed whales it has a double air duct leading up to it and the blowhole is located left of center.

The trachea only connects to the blowhole and there is no connection to the esophagus as with humans and most other mammals. Because of this, there is no risk of food accidentally ending up in the animal's lungs. The advantage of the blowhole is mainly that allows the animal to come up for air without having to stop or slow down much.

Animal anatomy