Alan, I'm in no way wanting to belittle the efforts of these guys, I think what they do is just great, but they represent the visible tip of a huge effort in this country, much of it volunteer, to control introduced predators & try to protect our native birdlife. There are several "inland islands" in different parts of the country, one of them in Nelson Lakes Park near me, where Kiwi have been reintroduced. These relay on a ring of traps to keep predators out. This in turn relies on endlessly patrolling these traps to rebait & reset as necessary. A huge effort & heros all, just like these guys. The catch word in all this, is introduced pedators, rats, weasels, stoats, ferrets, possums. We are lucky we don't have foxes & bigger predators. Until mankind arived in NZ we had none at all, other than hawks, hence our birdlife evolved in the absence of predators & are especially vulnerable.
On the other hand, Roe deer aren't predators, & I reckon we could do with a few of these.

Steve