Wharfin:
The wharfin of planet Skelaria spend half their lives in the waters of Horatia, and the other half in the Seas of Mehluna. These bodies of water are a great distance apart , making their migration times quite lengthy. Luckily, wharfin can keep half of their brains awake while sleeping. This is called Unihermispheric Slow Wave Sleep, USWS, and it allows the wharfin to move through their migration routes without stopping, which would make them vulnerable to predators.
One eye open all the time,
The other one asleep.
I follow when it’s time to move,
Making nary a peep.