The sanctuary is back to its pest-free state and DNA testing has been completed on the 26 Norway rats caught a few months back. With the aid of some earlier profiling of the genetics of rats in the Auckland region it was then possible to work out where our invaders had come from. Luckily the DNA profile of Norway rats from Gulf Harbour and Shakespear is significantly different from the rest of the region, and this showed that our rats were all local.
The genetic analysis also looked at the relatedness between individuals (were they siblings & cousins or just unrelated neighbours?), finding that they all descended from 5-7 mothers and fathers.
This all means that the rats either came around or through the fence or that they hitched a ride on a local vehicle or boat, though its not possible to tell how many bred inside versus outside the sanctuary. It also underlines the need for eternal vigilance by visitors and for a long-term system of trapping and surveillance in the sanctuary. Incursions will happen again, so its good to know that our system can cope.