I find this quite surprising (especially as an Australian) but it is interesting. I don’t think the same is true for invasive mammals – particularly during the early stages of an invasion. That said, when native mammals are reintroduced or return they can get up to a very high density. Northern Quolls all but disappeared from the Cooktown area after invasive Cane Toads arrived. But (and I am guessing here) a core population must have clung on that was tolerant of the toads and eventually it recolonised the area. A mate of mine said that when the Quolls returned they did so in large numbers – he saw 20 during a 30 minute drive home from town one evening.