Rodents invade ‘rat-free’ Ulva Island

Rats have been found on 'rat-free' Ulva Island. Photo courtesy of Greg Lind/DOC

Fears they are now breeding
January 2011: Twelve rats have been caught on ‘rat-free' Ulva Island in the last two weeks, raising concern for other animals on the wildlife reserve. After four rats were caught on Ulva Island last summer, Department of Conservation staff were hopeful that the incursion to this rat free island had been contained. However, in October a keen-eyed member of the public passed on a photo of animal prints he took in a muddy creek on the island. DOC experts confirmed that these were made by a rat.

Ulva Island has a network of traps and poison bait stations that are run year round to kill any rats that may get to the island. Extra traps were added to this and the frequency of checks increased. Tracking tunnels were also used to try to detect any rats on other parts of the island. Between August and December, no further rats were caught or detected. This all changed after Christmas Day - a total of 12 rats have since been trapped. Of greatest concern is that one of the rats was a juvenile, which indicates there is now a breeding population on the island.

Traps and tunnels now checked on a weekly basis
DOC staff have been diverted from other work to check the traps and tunnels on a weekly basis. A DOC team of experts will meet shortly to plan a course of action to remove rats from Ulva Island as rapidly as possible.
Ulva Island (256ha) is located in Paterson Inlet, Stewart Island. It is a key eco-tourism destination due to its pristine forest and abundant wildlife. Rats were initially removed from Ulva Island more than 13 years ago and the island is now home to many endangered birds. Ulva Island is one of a few ‘open sanctuary' islands where the public are able to visit without a permit.

Rats arrive by boats
‘Since rats were first removed from Ulva Island, on average one rat a year manages to get to Ulva Island either by swimming or hitch-hiking with boats. To date, we have managed to catch these rats as they arrive, preventing them from breeding. This is the first time a rat has evaded all of our traps, established and bred,' said DOC Biodiversity Manager Brent Beaven. ‘Ulva Island is a special place in Rakiura National Park and hundreds of thousands of visitors have enjoyed the island and its vibrant bird life over the past ten years.

‘Removing and then keeping rats off the island is a difficult task and there is always a chance that we may not succeed. DOC has an excellent record in this field but as always we will need the help and support of the public to achieve this,' said Mr Beaven.