Some idea as to when this musical intrusion
occurred may be obtained from Chaloupka's chronology of the rock
art of the Arnhem Land Plateau.
While maintaining that a study of rock art can provide important insights into the prehistory of Australia, Chaloupka considers it possible to position art periods, phases and styles of the plateau region between 'time indices given by known climatological, geomorphological and archaeological data, and by zoological and botanical evidence'. His three basic periods are named 'pre-estuarine', 'post-estuarines' and 'post-contact'.
Chaloupka's 'post-estuarine' period, which dates from about 1,000 years BP., possibly later, is marked by rock paintings which depict estuarine species such as barramundi and salt-water crocodile.
In addition to introduced species the paintings documents new weapons, including a multiplicity of spear types and the spear thrower. Boomerangs are conspicuous by their absence from post-estuarine paintings. Chaloupka's 'post-estuarine' appears to correspond, in part at any rate, with the 'late Mimi' rock art period of Brandl (1973).
Having stressed that breeding grounds for magpie geese, whistle ducks and other water birds would have been available after fresh-water swamps had replaced salt marsh plains, and noted that rock paintings of the plateau area depict flora such as the red lily, introduced with the development of fresh-water lagoons and the like, Chaloupka adds that in the most recent paintings hunters are to be seen 'carrying a "goose spear", a light, short bamboo spear tipped with a silver of hardwood, and a goose wing fan' (the function of the latter, still used the region, is to fan the embers of a fire into flame).
At the beginning of this last ecological change, the didgeridu made its appearance in rock paintings; and, as Chaloupka has noted, 'the people associated with this instrument carry a goose wing fan'.