Dr. Desley Whisson
Deakin University, Victoria, Australia

Introduction

Landscape modification through urbanisation, agriculture, and associated human activities is a leading driver of biodiversity decline worldwide. These changes reduce native vegetation to fragmented and isolated patches, often degrading habitat quality and increasing stressors such as noise and light pollution. Many wildlife species respond by contracting their ranges or altering behaviours—responses that have profound effects on health, reproduction, and survival.

Koalas (Phascolarctos cinereus), due to their specialised diet, limited mobility, and low reproductive rates, are especially susceptible to these impacts. While populations in parts of Queensland and New South Wales are listed as endangered, populations in Victoria and South Australia are believed to be stable, though few long-term studies have confirmed this.

The Mornington Peninsula in Victoria is a highly modified landscape with a mosaic of urban, rural, and remnant bushland areas. This case study explores the current distribution of koalas in this landscape, identifies key environmental and anthropogenic factors influencing their presence, and suggests targeted conservation strategies using passive acoustic monitoring techniques.

Study Region and Context

Location: Mornington Peninsula, Victoria (~73,000 ha)

Land Use: Mix of urban development, agriculture, bushland reserves, and coastal habitat

Native Vegetation: ~30% remains, 10% of which is within reserves

Koala History: Low-density population, likely reintroduced from French Island in the mid-20th century

Methods

Survey Design

• Passive Acoustic Monitoring: 123 sites monitored using autonomous recording units (ARUs) during the 2019 breeding season

• Sampling Period: 7 nights per site, from 20:00–02:00 h

• Detection Metric: Presence of male koala bellows

• Spatial Scale Analysis:

  • Site scale (100 m radius): Local tree cover, land use disturbance, anthropogenic sound (NDSI)

  • Landscape scale (1 km radius): Tree cover, road density, fragmentation indices (CAI_MN, ENN)

Data Analysis

• Occupancy Modelling: Single-season models accounting for imperfect detection

• Variable Assessment: Weather (affecting detection), tree cover, road density, fragmentation

• Predictive Mapping: Based on strongest predictors, mapped at 1 ha resolution

Key Findings

Detection and Occupancy

• Detection Rate: Koalas detected at 31% of sites; nightly detection probability = 0.363

• Influencing Factors:

  • Detection: Negatively affected by inclement weather

  • Occupancy:

    • Positively associated with landscape-scale tree cover

    • Negatively associated with road density

Predictive Modelling

• High Probability Habitat:

  • 7.08% (51 km²) of the Peninsula has ≥75% probability of koala presence

  • Most high-probability areas are in or near public reserves or HMAS Cerberus military land

• Public vs. Private Land:

  • Public land: 17.38% supports high-probability koala habitat

  • Private land: Only 4.75%, mostly grazing or rural residential

• Conservation Opportunity Zones:

  • ~85 km² identified where increasing tree cover could significantly enhance koala presence

  • 87% of this land is under private tenure

Discussion

Importance of Landscape-Scale Factors

Koala presence is strongly influenced by landscape tree cover and road density. Site-scale factors (e.g., presence of food trees, sound levels) had minimal explanatory power, likely due to the consistent availability of koala food species and high overall habitat fragmentation.

Role of Public Land

Protected reserves serve as important habitat and potential source populations. However, these cover a limited area, and long-term conservation requires enhancing connectivity and habitat availability on private land.

Conservation Risks

High road density is correlated with lower koala occupancy and higher mortality risks (e.g., vehicle collisions, dog attacks). Wildlife shelter records support these findings, with vehicle collisions accounting for ~70% of koala admissions on the Peninsula between 1987 and 2006.

Conservation Recommendations

1. Habitat Restoration:

   • Target tree planting in areas with 30–68% existing tree cover and road density <1 m/ha

   • Focus on rural private land to build habitat corridors

2. Connectivity Enhancement:

   • Link isolated patches using road verges, riparian zones, and paddock trees

   • Prioritise zones adjacent to major reserves

3. Threat Mitigation:

   • Install fencing and wildlife crossings along major roads (e.g., near Arthur’s Seat)

   • Implement dog control measures in koala-prone areas

4. Further Research:

   • Examine influence of anthropogenic noise on koala communication

   • Use bioacoustic indices (e.g., NDSI) in behavioural studies

5. Monitoring and Policy:

   • Regular acoustic surveys to track population changes

   • Incentives for private landholders to engage in habitat creation

Conclusion

Koalas on the Mornington Peninsula are present but likely at low densities due to habitat fragmentation and urban pressures. Despite challenges, there is significant potential to improve their conservation status through targeted reforestation, road safety measures, and collaboration with private landholders. The use of passive acoustic monitoring has proven to be a cost-effective and scalable method for guiding such efforts and should be adopted more widely in koala conservation programs.