All I know is that it has something to do with a kangaroo.
Buldozer of the bush is usually used to refer to wombats. Since wombats are very distantly related to kangaroos that is probably the answer. However since no wombats live in the outback it is totally incorrect to refer to them as bulldozer of the Outback bush. Wombats are inhabitants of coastal and subcoastal regions. The closest wombats get to the outback is a tiny colony just 400 km inland. That is at least 400km short of anywhere that could be referred to as outback.
