Grey petrels breed in the sub-Antarctic winter, and they are recolonising Macquarie Island. The species was widespread, though rare, on the island in 1911, then disappeared. Its return was first recorded in 1999, the same period as cat control and the later eradication of feral cats (Felis catus) by rangers from the Tasmania Parks and Wildlife Service.
The recolonisation has continued since the Macquarie Island Pest Eradication Project removed rabbits, rats and mice. The project was managed by PWS in partnership with the Australian Antarctic Division. Rat removal ended direct predation on eggs and juveniles. Rabbit removal ended competition for burrows and let dense tussock vegetation recover, and that vegetation is critical breeding habitat. The sequence is a rare good-news line in sub-Antarctic conservation, and it is an eradication payoff.
Pest eradication restored the breeding habitat
Grey petrels transport marine-derived nutrients from the Southern Ocean back to land, enriching the island's coastal and terrestrial ecosystems. Their return therefore does more than add a species back to the island list. It restores part of the nutrient cycle.
Most Southern Ocean petrels breed in summer. Grey petrels are the exception. They hunt and raise a chick through sleet, snow and relentless wind. A pair lays a single egg in March or April, the egg hatches in May or June, and the chick remains in its burrow for more than 100 days before fledging in spring. That winter breeding schedule makes the island's weather part of the habitat the surveys have to work with.
A survey is checking burrows not monitored since 2018
This winter, the wildlife team of AAD Wildlife Biologist Dr Sarah-Lena Reinhold, Wildlife Ranger Karina Sorrell and Ranger in Charge Gemma Rushton is surveying grey petrel breeding sites across Macquarie Island that have not been monitored since 2018. The birds nest in burrows, so the team uses burrow scopes to inspect nests and spends the available daylight hours, inevitably covered in mud, crawling through dense tussock to locate burrows and record breeding activity, including adults incubating eggs and the presence of chicks.
Surveys will be conducted over several years to produce an updated island-wide population estimate. The estimate will improve understanding of the status and population trend of this threatened species, and will guide conservation work under the Agreement on the Conservation of Albatrosses and Petrels. The work is part of the multi-agency Macquarie Island Wildlife Monitoring Program.
Fisheries bycatch remains the greatest global threat
Returning to Macquarie Island does not make the species secure. The threats extend throughout the grey petrel's breeding range. Incidental capture in commercial longline fisheries remains one of the greatest causes of mortality globally. Climate change is altering oceanic conditions and prey distribution across the Southern Ocean. Marine pollution, including plastic debris, adds further risk.
Continued efforts to reduce fisheries bycatch, eradicate introduced terrestrial predators from breeding sites, and protect and restore breeding habitat remain essential. The Macquarie Island story shows what predator eradication can achieve: a breeding seabird returning to an island after the pests are gone. The updated population estimate, due after several years of surveys, is the figure that will show whether the recolonisation is becoming a recovery.