Some mobs in the Treasures of Aht Urhgan areas are diurnal: they sleep during the nighttime, and are active during the daytime (but the specific hours may vary 
). When they are asleep, they do not move around, aggro or link, even though they might normally do so.
Diurnal is the opposite of Nocturnal.
Eruca, Ziz, and Wild Karakul are known to be diurnal. Jnun are known to be nocturnal.