The feathers which extend out from Hoothoot's eyes rotate around them completely in twenty-four hour cycles. At sunrise on the equinox (although varying times throughout the year) the tufts will cross their eyes, signaling to them that it is time to fall asleep. Some determined insomniacs attempt to stay up later, finishing what they are doing with a restricted field of vision; others go back to sleep when they awake to find the bottom of their eyes blocked by clock feathers.
These tufts are of course called clock feathers, for it was them which inspired the clock. They are not identical to pure clocks; their two hands are always at the same angle and solely tell the hour. (Minute hands and twelve-hour clocks are of course the inventions of clockmakers, and have no counterparts on Hoothoot.) In fact, they are responsible for the very concept of the hour, for when standing, they switch legs every sixty minutes. Indeed, there have been many kings and presidents throughout history who did not trust in the accuracy of clocks and declared their own Hoothoot to be the official timekeeper for all government purposes.
Interestingly, despite its relative rarity in Sinnoh as compared to Johto, Hoothoot actually appear more frequently in the art and iconography with the region. There, they are depicted as Dialga's loyal companions, and even ordinary Hoothoot are said to reach Dialga's ears by speaking while standing on both legs. Given their reluctance to use both legs except in times of grave danger, perhaps there is something to this tale after all.