Editing Cetacea (section)

=== Sleep ===
Conscious breathing cetaceans [[sleep]] but cannot afford to be [[unconsciousness|unconscious]] for long, because they may [[drowning|drown]]. While knowledge of sleep in wild cetaceans is limited, toothed cetaceans in captivity have been recorded to exhibit [[unihemispheric slow-wave sleep]] (USWS), which means they sleep with one [[brain hemisphere|side of their brain]] at a time, so that they may swim, breathe consciously and avoid both predators and social contact during their period of rest.<ref>{{cite journal | vauthors = Sekiguchi Y, Arai K, Kohshima S | title = Sleep behaviour: sleep in continuously active dolphins | journal = Nature | volume = 441 | issue = 7096 | pages = E9-10; discussion E11 | date = June 2006 | pmid = 16791150 | doi = 10.1038/nature04898 | s2cid = 4406032 | bibcode = 2006Natur.441E...9S }}</ref>

A 2008 study found that sperm whales sleep in vertical postures just under the surface in passive shallow 'drift-dives', generally during the day, during which whales do not respond to passing vessels unless they are in contact, leading to the suggestion that whales possibly sleep during such dives.<ref>{{cite journal | vauthors = Miller PJ, Aoki K, Rendell LE, Amano M | title = Stereotypical resting behavior of the sperm whale | journal = Current Biology | volume = 18 | issue = 1 | pages = R21-3 | date = January 2008 | pmid = 18177706 | doi = 10.1016/j.cub.2007.11.003 | s2cid = 10587736 | doi-access = free | bibcode = 2008CBio...18..R21M }}</ref>