Many small to medium-sized native mammals are rapidly declining across northern Australia, even in nationally-protected conservation reserves. Scientists believe that feral cats and changed fire regimes are major contributing factors in these declines, however infectious and non-infectious diseases may also play a role.

A two-year study investigating the role of disease in mammal decline is now underway, drawing together researchers from Murdoch University, the Northern Territory Department of Land Resource Management, James Cook University and Charles Darwin University. Murdoch University’s Dr Andrea Reiss has been undertaking the majority of the analysis.

What sorts of diseases are affecting small mammals?

There are a range of infectious diseases that can impact small mammal populations. These include viruses, bacteria, blood-borne parasites and other organisms. Some diseases may directly impact animals, causing them to die, or indirectly, by reducing reproductive rates or the survival of young.

In more subtle cases, an animal’s behaviour may change, making them more vulnerable to predators. For example toxoplasmosis is a parasitic disease which reduces a mammal’s coordination and agility.

Which species are being investigated?

Common brushtail possum (Trichosurus vulpecula)
Bandicoots, northern brown (Isoodon macrourus)
Northern quoll (Dasyurus hallucatus )
Brush-tailed rabbit-rat (Conilurus penicillatus)

Two key feral mammals are also being investigated for their role in disease transmission: black rats (Rattus rattus) and feral cats (Felis catus).

Where are the researchers sampling?

Areas around Darwin and remote sites in the Northern Territory are being sampled:

• the native woodlands of Bathurst Island
• Cobourg Peninsula
• the Kapalga area of Kakadu (east of Jabiru, north of the Arnhem Highway)
• East Alligator River region
• Groote Eylandt.

What does the field work involve?

Animals are captured in cage traps and anaesthetised. While the animal is asleep, it is thoroughly examined and data collected on its weight, age, gender, reproductive status, and the condition of its teeth, body and coat.

Dr Reiss then checks the animal for any signs of ill health by listening to its heart and lungs with a stethoscope, gently palpating its abdomen and limbs, looking in its mouth, eyes, and ears, and taking its temperature. The animal’s blood oxygenation, heart and breathing rate are also measured. Samples of its blood, fur, faeces, and urine are taken, along with swabs from its mouth, eyes, and genitals, for laboratory testing.

How will this research be used?

For the future of these species and their ecosystems, it is important to better understand how disease may affect mammals in the years to come. If mammal numbers continue to fall and populations become more isolated, genetic diversity will diminish and the threat of disease will grow.

This study will provide more information on health and disease in native mammal populations in the Top End and will investigate whether disease is contributing to the population declines.

View more information about this study.