Hawaiian seabirds recover following rat eradication

After being declared rat-free in 2021 following a decades-long eradication programme, monitoring efforts have indicated a seabird success story on a small island in Hawaii.

Increased breeding success has been noted among seabirds on the 115-ha Lehua Island, an uninhabited island off the north coast of Niʻihau that is also a state-designated seabird sanctuary.

Lehua was declared rat-fee in 2021 after many years of work to eradicate non-native rats and rabbits (commons.wikimedia.org).

Recent surveys documented more than 25,000 pairs of 11 seabird species nesting or attempting to nest on Lehua. Wedge-tailed Shearwater (23,000 pairs) is the most numerous species, with around 1,300 pairs of Red-footed Booby and 520 pairs of Brown Booby also present. Christmas Shearwater, Bulwer's Petrel, Red-tailed Tropicbird and Black Noddy also breed, while small but growing colonies of Laysan (28 pairs) and Black-footed Albatross (16 pairs) are internationally significant for Lehua is one of the few high islands where they nest (other colonies are at risk from rising sea levels).

According to Hawaii's Department of Land and Natural Resources (DLNR), seabird work on Lehua is now in the restoration phase. This aims to attract more native seabird species and establish breeding populations of endangered native birds. Social attraction systems were installed at two different sites on the island in January.

One of the sites targets several tern species that no longer breed on Lehua: Sooty Tern (which breeds on nearby Kaʻula Islet), Spectacled Tern and Blue Noddy. This is the first social attraction project for terns in the Hawaiian Islands. These focal tern species are protected by the Federal Migratory Bird Treaty Act and State law.

Thirty tern decoys, a sound system and 10 mirror boxes are in place at the site. This method has been used successfully for terns in other parts of their range and are effective because of the nature of these species. The creation of an apparent colony through decoys, mirror boxes, and calls played through sound systems helps to create what appears to be a large active tern colony. This attracts prospecting birds into the area and helps promote breeding behaviour.

Wedge-tailed Shearwater is the most numerous breeding seabird species on Lehua (Kit Day).

For the endangered Band-rumped Storm Petrel and Hawaiian Petrel, artificial nestboxes, a social attraction sound system and monitoring cameras have been deployed. This technique has been successfully used in other parts of the world for this species. Band-rumped Storm Petrels are regularly recorded calling around Lehua, but a burrow has never been located.

This work was partially funded by a US Fish and Wildlife Competitive State Wildlife Grant, and the National Fish and Wildlife Foundation, as well as by state funds. Volunteers and Kauaʻi-based Archipelago Research and Conservation helped the project team install the social attraction systems on Lehua.

More information on Lehua and its seabirds can be found here.