DNA study solves mystery of rats returning to Lord Howe Island

Researchers conducting DNA testing on black rats rediscovered on Lord Howe Island in 2021 have traced the animals to the island's prior rat population rather than to any population on Australia's New South Wales mainland. The finding has reignited scientific debate about how these rodents managed to persist through what was believed to be a complete eradication programme.

Lord Howe Island, located off the east coast of Australia, had been considered rat-free following previous elimination efforts. The unexpected reappearance of the rodents nearly two decades later surprised conservationists and prompted immediate investigation into their origins.

Genetic analysis proved instrumental in determining that the newly discovered rats shared ancestry with the island's historical rat population rather than representing an invasion from external sources. This revelation has raised significant questions about the effectiveness of the earlier eradication campaign and whether some rats may have survived in isolated pockets of the island.

Following confirmation of the rats' origins, authorities have launched a fresh eradication initiative to eliminate the newly returned population. The incident has highlighted the challenges of maintaining rodent-free status on islands and the importance of long-term monitoring programmes to detect any resurgence of invasive species.