Aboriginal as a noun (plural - aboriginals), can be used to refer to a plant or animal that is native to a region. For example, "this bird is an aboriginal of this region." Using aboriginal without a capital "A" to refer to anything associated with people may cause an offence. In Canada, where I am from, style manuals recommend against using the noun Aboriginal for a person or people. Aborigine as a noun (plural - Aborigines) refers to an individual aboriginal Australian. In other words, Australia's First Nations people.