Lore Bit:
Delthulians have an affinity for senses and perception in all forms. Eyesight which can rival a hawk, smell that can discern the smallest trace of scent, ears sensitive enough to hear the heartbeat of a stalker in hiding.
This makes them exceptional trackers, but also means they can suffer from sensory overload.
Zen, even though halfblooded, inherited these traits, allowing his team the opportunity to sleep while he watches their campsite.