Few rats remain on Lehua island after 2 years of treatment

State officials say that a rat control program appears to be working at Lehua Island nearly two years after its inception.

The state Department of Land and Natural Resources announced this week that the population of invasive rats remains extremely low following three applications of rodenticide to protect the island, which is a seabird sanctuary.

“The monitoring data collected on Lehua Island suggests that the population of Pacific rats remains extremely low,” said Mele Khalsa of Island Conservation, a partner organization, in a news release.

Khalsa said the group has seen no signs of rats eating eggs or chicks since the island was last treated on Sept. 12, 2017.

The island, however, has not been completely rat-free since the treatments began. In January 2018, a rapid assessment team headed to the island after two rats were found via motion-detecting field cameras.

DLNR last summer deployed two rat-sniffing dogs to the island to help detect where rodents could still be living.

Khalsa said no rats have been detected by camera since December 2018, or seen in traps or tracking tunnels. However, the monitoring team in early-to-mid 2019 detected what appeared to be rat fecal pellets, and will continue to keep an eye out for any remaining presence of rodents.

André Raine of the Kaua‘i Endangered Seabird Recovery Project said the team continues to see positive changes for the native breeding birds on Lehua.

“Most notably, the Bulwer’s petrels have responded quickly to the rat eradication project.,” said Raine in the release. “These small seabirds are easy prey for rats and the fact that they are increasing is a great sign.”

In addition, Raine said the group recently discovered two nests of the native black-crowned night heron, or aukuu, which is the first breeding record of this species on Lehua.

The aerial drop of rat bait pellets containing the rodenticide, diphacinone, initially sparked community concerns over adverse impacts on the surrounding waters and other wildlife.

Sheri S. Mann, Kauai Branch Manager for the DLNR Division of Forestry and Wildlife, said monitoring continues to show no negative impacts from the rat bait pellets on the surrounding environment. She noted the presence of denser vegetation and reduced run-off, resulting in healthier reefs and increased sea life.

DLNR said last year the U.S. Department of Agriculture, National Wildlife Research Center released a final monitoring report that detected no rodenticide residues in samples of water, soil, opihi, or seabirds, and minimal impacts to any species other than rodents.

Field teams will continue to make regular monthly monitoring trips to Lehua, and will do spot treatments if rats are detected. The ultimate goal is the complete eradication of Pacific rats from Lehua Island.