The Australian Antarctic Program is supporting post-eradication monitoring to assess how Macquarie Island’s wildlife is recovering following the removal of invasive pests in 2011–2014.
After the productivity of summer, island life has slowed right down. As the landscape has turned from green to brown, many of the species this project is studying have left, but they’ve been replaced by winter-breeding Grey Petrels. Preyed upon heavily by cats, these beautiful seabirds went extinct on Macca during the 20th Century, but began to recolonise in the late 1990s when the last cats were killed.
All seabirds play a hugely important role transferring nutrients from sea to land where their guano enriches island soils. As a result, the tussock grass growing in seabird colonies is especially lush and nutrient rich — qualities which made it particularly palatable to rabbits. When the rabbit population exploded on Macquarie in the early 2000s, the vegetation in seabird colonies was heavily grazed and these areas became denuded. This destabilised soils with devastating impacts for burrowing seabirds — burrows collapsed as soils washed away. Owing to these threats Grey Petrels are listed as Endangered under Tasmanian State legislation.
All of this is now thankfully in reverse. The number of Grey Petrel burrows monitored by the Tasmania Parks and Wildlife Service has increased year on year, and the tussock grass they’re found in is once again tall and lush. So much so, it is now increasingly impenetrable, criss-crossed by a maze of tunnels at ground-level which the birds keep open as access roads to their nesting burrows. Many of the island’s petrel colonies are safeguarded within Special Management Areas so we rarely witness the drama within.
By day they are tranquil, but at night they come alive as birds return from sea. The rapid regrowth of the island’s vegetation, and the nocturnal behaviour of seabirds at their colonies present real challenges for monitoring their recovery into the future. Coupled with a desire to minimise disturbance within colonies, this is driving the development of new approaches to monitoring using emerging technologies.
At Macquarie we’re using remote microphones to record the night-time cacophony of noise as breeding birds hose their songs into the night from perches atop tussock heads, and remote cameras are observing the comings and goings of birds from the colony. These are designed as low cost, low impact ways to set baselines, and monitor population changes into the future.
By Jez Bird, PhD student with the University of Queensland, supported by a scholarship under the Research Training Program, and AAS Project 4305.