The study, published in Science, found species categorized as extinct in the wild (EW)—populations solely found outside their natural habitat, such as in captivity—could have their declines prevented and reversed with urgent international effort.

Species include the Sihek (Guam kingfisher), the ʻalalā (Hawaiian crow) and Partula snails from the South Pacific; and in Australia, the Christmas Island blue-tailed skink and Lister's gecko.

"The loss of these species can have a ripple effect on entire ecosystems, and if we don't take urgent action, the consequences could be catastrophic," Dr. Carolyn Hogg, co-author of the study, said.

Dr. Hogg is part of the University of Sydney's School of Life and Environmental Sciences and co-leads the Australasian Wildlife Genomics Group. She is also a member of a global task force of the International Union for Conservation of Nature (IUCN), whose mission is to develop methods to boost the profile of EW species.

Dr. Hogg and colleagues examined 84 EW species on the 2022 IUCN Red List, 72 of which remain in the category while four have become extinct. A further 21 EW species dating back to 1950 have had their status change—12 have been returned to nature, but nine have gone extinct.