He is one of a large group of volunteers dedicated to creating a Predator Free Port Hills, although he has mixed feelings about his job.
"You know it is sad that we are killing, you know, animals that are beautifully adapted to their environment," McDonald said.
"But in some ways ... the greater good is to preserve our native species. There are rats all over the world but most of our native species are only found here."
Over the past four years, he has caught 160 rats using methods like ceramic bait.
He says rats are a bit like humans - they look for the easiest way to achieve their objectives. And trappers can take advantage of this potential weakness.
"Rats are like everybody else. They are cautious of going out into the open so you can’t put your traps out in the open, and they tend to be kind of lazy.
"They follow natural paths, so if there’s a natural path then that is a good place to put a trap."
The information he collects is shared with predator-free groups across New Zealand to help other trappers.
- By John Spurdle
- Public Interest Journalism funded through NZ On Air
