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Three mammal species, once locally extinct – the bush rat (Rattus fuscipes), the eastern pygmy possum (Cercartetus nanus) and the brown antechinus (Antechinus stuartii) – are returning to the headland.
Small in size but mighty in ecological impact, these native mammals are vital pollinators for the diverse plants that make up the area’s critically endangered Eastern Suburbs Banksia Scrub (ESBS) ecological community.
The bush rat: taking back the headland
Urbanisation, habitat destruction and the relentless pressure of feral cats (Felis catus) and foxes (Vulpes vulpes) once wiped out North Head Sanctuary's native bush rat (Rattus fuscipes) population, leaving a vacuum quickly filled by the invasive black rat (Rattus rattus) – a species that can aggressively outcompete small native mammals for habitat and prey upon bird eggs.
From 2014 to 2016, a Harbour Trust contractor specialising in ecology took action, collecting 180 genetically diverse bush rats from Ku-ring-gai Chase National Park and Muogamarra Nature Reserve, microchipping each one before releasing them at North Head Sanctuary. Annual microchipping and tissue collection has since allowed survey teams to closely monitor the genetic diversity of the population over time.2 Following the reintroduction of the bush rat and extensive control of the invasive black rat, black rat population numbers declined dramatically – from an estimated 112 in 2019 to 29 in 2020, then nine in 2021, with even fewer recorded in a 2025 survey. Meanwhile, the bush rat population surged by 150% from winter 2023 to winter 2025.
In June 2026, a new cohort of native bush rats was translocated from Ku-ring-gai Chase National Park and Muogamarra Nature Reserve to North Head Sanctuary, further strengthening the genetic diversity of the area’s growing population. This activity is part of the ‘Urban Rewilding’ project led by Dr Thomas Newsome and PhD candidate Mareshell Wauchope. The project team includes Harbour Trust's specialist contractor Anderson Environment and Planning (AEP) in collaboration with Taronga Conservation Society, the NSW Government and seven local councils in northern Sydney.
The eastern pygmy possum: a tiny pollinator with a big purpose
Weighing less than 45 grams and measuring just over 10 centimetres in length, the eastern pygmy possum (Cercartetus nanus) is one of the smallest possums in the world and one of North Head Sanctuary’s most important. They are prolific pollinators of the ESBS ecological community; however, habitat destruction and the impacts of fire disturbance on nectar-producing plants had caused their population to collapse.
Since 2016, eastern pygmy possums have been steadily reintroduced to North Head Sanctuary from national parks across Sydney. The most recent relocation, carried out between February and April 2023, saw up to 12 possums translocated from Ku-ring-gai and Garigal National Parks by a Harbour Trust ecologist contractor. Population numbers have grown steadily from 2018 to 2023. The 2026 surveys recorded a slight decrease in eastern pygmy-possum detections, although this was likely driven by unseasonably warm weather negating or delaying the need to seek refuge in nest boxes. Out of the 30 total captures, 47% were juveniles and 17% were females with active pouches – both encouraging signs of active breeding.
The brown antechinus: a nimble carnivore making a comeback
Small and swift, the brown antechinus (Antechinus stuartii) is a carnivorous native mammal that feasts on insects and small reptiles, while also playing an important role in the pollination of Australia's flowering plants. Decades of urban development, habitat loss and feral animal predation saw their numbers at North Head Sanctuary dwindle to local extinction. Since 2017, Harbour Trust has been working with specialist contractors to change that, relocating microchipped individuals from Ku-ring-gai and Garigal National Parks and establishing them in nest boxes across the headland.
A 2025 Annual Survey, encompassing 55% of survey sites, detected 22 individuals during the winter season, a two-fold increase from the summer survey, revealing a strong male bias with individuals in good reproductive condition. Long-term monitoring also shows the brown antechinus expanding into multiple new locations across North Head Sanctuary.
Tiny engineers keeping the area in balance
Through more than a decade of collaborative monitoring and species reintroduction works from Harbour Trust and their contractors, the bush rat (Rattus fuscipes), eastern pygmy possum (Cercartetus nanus), and brown antechinus (Antechinus stuartii) have been brought back from local extinction. Growing populations, healthy breeding activity and increasing numbers of pouch young are all promising signs these populations are establishing themselves well at North Head Sanctuary. These native mammals are far more than conservation success stories. They are tiny engineers of the ecosystem, spreading seeds, turning soil and keeping populations in balance.
Fauna species survey data sources: Harbour Trust contractors specialising in ecology, including Anderson Environment and Planning
