of cetaceans that have been proven experimentally to use usws in order to maintain both swimming patterns and the surfacing for air while sleeping. in addition, a reversed version of the "group edge effect" has been observed in pods of pacific white-sided dolphins. dolphins swimming on the left side of the pod have their right eyes open while dolphins swimming on the right side of the pod have their left eyes open. unlike in some species of birds, the open eyes of these cetaceans are facing the inside of the group, not the outside. the dangers of possible predation do not play a significant role during usws in pacific white-sided dolphins. it has been suggested that this species utilizes this reversed version of the "group edge effect" in order to maintain pod formation and cohesion while maintaining unihemispheric slow-wave sleep. rest during long bird flights while migrating, birds may undergo unihemispheric slow-wave sleep in order to simultaneously sleep and visually navigate flight. certain species may thus avoid a need to make frequent stops along the way. certain bird species are more likely to utilize usws during soaring flight, but it is possible for birds to undergo usws in flapping flight as well. much is still unknown about the usage of unihemispheric slow-wave sleep, since the inter-hemispheric eeg asymmetry that is viewed in idle birds may not be equivalent to that of birds that are flying. species exhibiting usws although humans show reduced left-hemisphere delta waves during slow-wave sleep in an unfamiliar bedchamber, this is not wakeful alertness of usws. cetaceans of all the cetacean species, usws has been found to be exhibited in the following species amazon river dolphin (inia geoffrensis) beluga whale (delphinapterus leucus) narwhal (monodon monoceros) bottlenose dolphin (tursiops truncates) pacific white-sided dolphin (sagmatias obliquidens) pilot whale (globicephala scammoni) false killer whale (pseudorca crassidens) porpoise (phocoena phocoena) orca (orcinus orca) sperm whale (physeter macrocephalus) pinnipeds though pinnipeds are capable of sleeping on either land or water, it has been found that pinnipeds that exhibit usws do so at a higher rate while sleeping in water. though no usws has been observed in true seals, four different species of eared seals have been found to exhibit usws including northern fur seal (callorhinus ursinus) significant research has been done illustrating that the northern fur seal can alternate between bsws and usws depending on its location while sleeping. while on land, 69% of all sws is present bilaterally; however, when sleep takes place in water, 68% of all sws is found with interhemispheric eeg asymmetry, indicating usws. southern sea lion (otari bryonia) steller sea lion (eumetopias jubatus) sirenia in the final order of aquatic mammals, sirenia, experiments have only exhibited usws in the amazonian manatee (trichechus inunguis). birds common swift the common swift (apus apus) was the best candidate for research aimed at determining whether or not birds exhibiting usws can sleep in flight. the selection of the common swift as a model stemmed from observations elucidating the fact that the common swift left its nest at night, only returning in the early morning. still, evidence for usws is strictly circumstantial and based on the notion that if swifts must sleep to survive, they must do so via aerial roosting as little time is spent sleeping in a nest. multiple other species of birds have also been found to exhibit usws including common blackbird (turdus merula) domestic chicken (gallus gallus domesticus), glaucous-winged gull (larus glaucescens) japanese quail (coturnix japonica) mallard (anas platyrhynchos). northern bobwhite (colinus virginianus), orange-fronted parakeet (aratinga canicularis) peregrine falcon (falco peregrinus) white-crowned sparrow (zonotrichia leucophrys gambelii) future research recent studies have illustrated that the white-crowned sparrow, as well as other passerines, have the capability of sleeping most significantly during the migratory season while in flight. however, the sleep patterns in this study were observed during migratory restlessness in captivity and might not be analogous to those of free-flying birds. free-flying birds might be able to spend some time sleeping while in non-migratory flight as well when in the unobstructed sky as opposed to in controlled captive conditions. to truly determine if birds can sleep in flight, recordings of brain activity must take place during flight instead of after landing. a method of recording brain activity in pigeons during flight has recently proven promising in that it could obtain an eeg of each hemisphere but for relatively short periods of time. coupled with simulated wind tunnels in a controlled setting, these new methods of measuring brain activity could elucidate the truth behind whether or not birds sleep during flight. additionally, based on research elucidating the role of acetylcholine in control of usws, additional neurotransmitters are being researched to understand their roles in the asymmetric sleep model.