Wednesday, January 3, 2018

Rats detected at Lehua, four months after major eradication effort

Rat control team on Lehua. Credit: DLNR
Rats are back at Lehua, or more likely, a few Pacific rats survive after a major effort to eradicate them during the late summer.

Wildlife management teams were on the island yesterday to better understand the extent of the rat presence and to establish extensive bait and trapping measures in the area where they were seen. They have not abandoned efforts to completely eradicate invasive rats from the small island.

The Lehua rat control project is designed to remove a major predator of the many species of seabirds that nest on the small island north of Ni`ihau. The island has been populated by Pacific rats at least for the past century. It is a state seabird sanctuary.

Pacific rats prey on eggs and chicks of many species, and they also damage the environment by eating seeds and seedlings of plants that otherwise would provide cover and nesting habitat for the birds.

This statement about the rat control project was released yesterday by the state Department of Land and Natural Resources:

Lehua's steep terrain. Credit: DLNR
“The invasive Pacific rat is a voracious predator on the eggs, chicks and even adult birds that currently breed and nest on remote Lehua. The restoration project team has stated repeatedly that the project will not be considered a success unless every invasive rat is removed from the ecosystem, and that will take a full year after the final application to say for sure. The goal of the Lehua Island Restoration Project is to provide safe, predator-free breeding habitat for native seabirds and other species so they may thrive again.”

Numerous motion detection cameras and human surveys of the island after the final delivery of diphacinone rat bait in September 2017 detected no rat presence. But camera memory cards collected in December revealed at least two rats near the summit of the island in late November.

The rats spotted on the camera cards are believed to be Pacific rats, the species that was abundant on the island before the eradication effort in August and September, although a positive identification from fuzzy black and white photos was not possible.

The team sent to the island yesterday included members from Island Conservation (IC), the state Division of Forestry and Wildlife and the Kaua‘i Endangered Seabird Recovery Project (KESRP.) 
The teams have installed a range of measures to attempt to assess whether there are more of the predators present on the island. A total of 134 monitoring devices have been placed on the island, including traps, tracking tunnels with ink pads to detect footprints, wax chewing blocks, bait stations and motion-detection cameras.
Many of the cameras are aimed specifically at seabird nests and burrows as part of the KESRP program, but will identify rat presence as well.

Rats have been eradicated from dozens of islands around the globe, and most eradications work the first time. However, a significant percentage has required repeat control efforts. In the case of Lehua, one theory was that winds at the top of Lehua blew rodenticide pellets away from the top of the ridge, allowing a few rats to survive there, while rodents elsewhere on the island were controlled.

“After seeing these two rats on camera, we collected, immediately reviewed, and noted locations of any additional images the cameras may have picked up,” said Mele Khalsa, of Island Conservation. A review of all other camera records identified no other rat photos.

“While we are clearly disappointed to see evidence of two rats on the island, we are very lucky our partners (KESRP) were able to detect them. We knew from the beginning there was the possibility that a few rats could linger. Now it’s important to address this,” said Suzanne Case, chair of the state Board of Land and Natural Resources.

The rat eradication program has been intensely controversial, largely over the fear that toxic baits could impact the marine environment. Tests on fish found around the island immediately after the bait distribution could not show that the rodenticide was an issue, and tests on the livers of pilot whales that stranded on Kaua`i a month later showed no presence of diphacinone.

Since the two rat detections were in the central part of the island, the current effort should not impact the coastline of Lehua.

© Jan TenBruggencate 2017

No comments: