Above picture: Lord Howe Island, a World Heritage Site in the Tasman Sea. Photograph by Ian Hutton
Terence O’Dwyer (Conservation and Restoration Science, Department of Planning and Environment, New South Wales, Australia) and colleagues have published in the journal Bird Conservation International on breeding recovery of the Black-winged Petrel Pterodroma nigripennis on Australia’s Lord Howe Island after the eradication effort directed at introduced Ship or Black Rats Rattus rattus.
According to Hank Bower, Manager Environment/World Heritage, Lord Howe Island Board, the last live rat was detected on the island on 28 July 2021. However, a formal announcement declaring the island’s freedom from rodents will only follow a final check two years after the last rodent was detected, so not prior to August 2023. But before then, the seabirds have made their own decision through their improved breeding success!
The authors’ finding, of a huge improvement in breeding success for the Black-winged Petrel from 2.5% in the presence of predatory rats to 67% immediately after the Rodent Eradication Project, bodes well for the fortunes of Marion Island’s burrowing seabirds, notably the Great-winged Petrel P. macroptera and the Grey Petrel Procellaria cinerea, which both breed in winter when the mice are at their most hungry.
A study by Ben Dilley and colleagues found that Marion’s Great-winged and Grey Petrel populations have not recovered as well as expected following the earlier eradication of feral cats, and were suppressed by the mice. Removing Marion’s mice should give these two species, and the rest of the island’s suite of burrowing petrels, the breeding boost they need. – just as has happened on Lord Howe with its Black-winged Petrels and on numerous other islands with breeding burrowing petrels following the eradication of rodents.
The Lord Howe paper’s abstract follows:
“In 2019, a Rodent Eradication Project (REP) was implemented on World Heritage listed Lord Howe Island, Australia. Among the species expected to benefit was a burrow-nesting seabird, the Black-winged Petrel Pterodroma nigripennis. Prior to the REP, we assessed causes of Black-winged Petrel nest failure using surveillance cameras. We also measured breeding success before and after the REP and investigated emerging pressures on breeding success from other native species. In 2017, ship rats Rattus rattus were a major cause of Black-winged Petrel nest failure, and breeding success was as low as 2.5%, compared to 47.5% on rodent-free Phillip Island (Norfolk Island Group). In 2020, in the absence of rodents, breeding success on Lord Howe Island increased dramatically to 67% and remained high (50%) in 2021. This result suggests that reproductive output of small seabirds has been heavily supressed by rodents on Lord Howe Island for decades. A subsequent increase in the population of a predatory endemic rail, the Lord Howe Woodhen Hypotaenida sylvestris, combined with burrow competition from Little Shearwaters Puffinus assimilis, indicated that initial high breeding success may not be sustained. However, the surge in successful breeding of Black-winged Petrels is likely to result in a significant increase in fledgling numbers and the recruitment of hundreds of additional birds each year. Given the important role of petrels in global nutrient cycling, and their positive influence on island biodiversity, their expansion should benefit the ecological restoration of Lord Howe Island.”
With thanks to Hank Bower, Manager Environment/World Heritage, Lord Howe Island Board.
Dilley, B.J., Schoombie, S., Stevens, K., Davies, D., Perold, V., Osborne, A., Schoombie, J., Brink, C.W., Carpenter-Kling, T. & Ryan, P.G. 2018. Mouse predation affects breeding success of burrow-nesting petrels at sub-Antarctic Marion Island. Antarctic Science 30: 93-104.
O’Dwyer, T., Carlile, N., O’Neill, L & Halpin, LR 2022. Changing fortunes of the Black-winged Petrel Pterodroma nigripennis following the Lord Howe Island Rodent Eradication Project – interactions with other recovering species. Bird Conservation International doi.org/10.1017/S0959270922000132.
John Cooper, News Correspondent, Mouse-Free Marion Project, 08 September 2022
The Mouse-Free Marion Project is a registered non-profit company (No. 2020/922433/08) in South Africa, established to eradicate the invasive albatross-killing mice on Marion Island in the Southern Ocean. The project was initiated by BirdLife South Africa and the South African Department of Forestry, Fisheries and the Environment. Upon successful completion, the project will restore the critical breeding habitat of over two million seabirds, many globally threatened, and improve the island’s resilience to a warming climate. For more information or to support the project please visit mousefreemarion.org.