From time to time the pelicans vanish from Encounter Bay - and the river and the Coorong and their other coastal haunts .
Mysteriously, they have been drawn away by floods in the state's north.
No one knows how the birds know that the salt lake, Lake Eyre, has been flooded or how they know the way there or to the other usually temporary inland lakes and waterways including Cooper Creek and Coongie Lakes. There may be a scent they can sense. There may be some meme, older birds leading the young. The theories are much-debated.
Lake Eyre floods only once in every few years - after big rains in Queensland. About 60 species of birds respond to its call - and six to eight million waterbirds make the pilgrimage. Some travel a thousand kilometers or more.
Weed and algae suddenly flourish and fish and crustaceans emerge on a fast-breeding cycle. www.desertfishes.org/australia/index.html
Pelicans, which like to breed in large colonies, will swiftly trample the surrounding plants into shallow nests and set to egg-laying.