Macquarie Island, a remote sub-Antarctic landmass, holds a unique position as a UNESCO World Heritage site due to its exceptional natural values. This isolated island, located roughly halfway between Tasmania and Antarctica, is characterized by its distinctive ecosystem, which evolved in relative isolation. For many years, however, the island’s delicate balance was disrupted by feral cats, an introduced species that posed a significant threat to its native inhabitants.
The Invasive Threat
Feral cats arrived on Macquarie Island with sealers or whalers around 1820, establishing a population by the 1830s. By the mid-1980s, these predators severely impacted the island’s unique wildlife. Initially, cats preyed on rabbits, another introduced species, but as rabbit numbers declined due to control efforts, they shifted their focus to native seabirds.
The cats’ hunting had devastating consequences for ground-nesting seabirds, which lacked natural defenses. At their peak, feral cats were estimated to kill approximately 60,000 seabirds annually. This predation contributed to the extinction of two native bird subspecies: the Macquarie Island parakeet and the Macquarie Island rail. Various petrel and albatross species, including seven listed by the Agreement on the Conservation of Albatrosses and Petrels (ACAP), were also severely impacted.
The Eradication Campaign
To address the severe threat from feral cats, a large-scale eradication project began on Macquarie Island. Initial control efforts started in 1974, integrated with other pest programs, intensifying in 1996. A dedicated eradication program commenced in 1998, aiming to remove the feral cat population.
The campaign employed various methods. Primary methods for initial reduction included cage trapping and shooting, with leg-hold traps used for remaining cats. A total of 761 cats were captured from 1996 to 2002.
The project recorded 6,298 field days and 216,574 trap nights, demonstrating the extensive effort involved. Challenges included the island’s remote location, harsh sub-Antarctic weather, and rugged terrain, making access difficult. The last cat was removed in 2000, a significant milestone for the island’s conservation.
Ecological Restoration and Broader Implications
Following the successful eradication of feral cats in 2000, Macquarie Island has experienced notable ecological recovery. Native bird populations have shown a resurgence, with burrow-nesting species like Antarctic prions, grey petrels, and blue petrels increasing in numbers. Blue petrels now number over 300 breeding pairs, and grey petrels have at least doubled their population to 200 breeding pairs. This recovery also extends to areas previously affected by rabbit grazing, which further damaged seabird breeding habitats.
The subsequent increase in rabbit and rodent populations highlighted the complex nature of invasive species management. This led to a broader, multi-species eradication project completed in 2014, which successfully removed all feral animals, including rats, mice, and rabbits. The Macquarie Island project serves as a globally recognized success story in invasive species management, offering valuable lessons for similar island conservation efforts worldwide.