Conservationists say they’ve successfully eliminated harmful, non-native rats from remote, uninhabited Palmyra Atoll.

The U.S. Fish and Wildlife Service, The Nature Conservancy, and Island Conservation said Monday they used rodenticide to kill the rats. Scientists confirmed last year the island is now rat-free.

Rats were likely introduced to the atoll about 1,000 miles south of Honolulu during World War II. The rat population on the 600-acre atoll grew as high as 30,000.

The rodents are harmful on Palmyra because they eat the eggs and chicks of native birds. They also eat land crabs and the seeds and seedlings of native tree species.

University of California, Santa Cruz researchers have detected a sharp increase in native tree seedlings, spiders, crabs and other indigenous species since the rats were killed off.