These large flying peaceful beasts spent their entire lives gliding through the desert winds of the Vulcan homeworld. It is said that they mated in the skies and never touched the ground. Not even the predatory Shavokh were known to hunt them. Despite this, they were known to be fragile animals and were believed extinct by the age of Surak and before the Sundering.
It was believed that the wars that were destroying the planet, as well as the pollution released into the atmosphere, had killed the Sundweller populations, however, a few were still known to be seen at the time. Due to the rarity in seeing these animals, it was believed that should one be seen then it should be considered an omen of bad things to come. (TOS - Vulcan's Soul novel: Exodus)