At one time, WDFW (Wildlife Program) wanted to define native species as those present in the state (if memory serves) in 1900. When it was pointed out that there were natural invasions occuring today, such as the Scrub Jay coming north, they did back off. Don't know if they ever arrived at a useful definition.

This issue, like many others in resource management, is not amenalble to logic. When WDW was creating their list of deleterious species, like mouflon and mute swan, they defined deleterious as (among other things) preying on native species. At the same time, they were agressively using Tiger Musky (non-native) to eat native pikeminnows.