Lost behind buffel grass

Kristin (Bluey) Donaldson, School of Biological Sciences, University of Queensland

Bluey Donaldson with a bridled nailtail wallaby
Photo © Bluey Donaldson

The bridled nailtail wallaby (Onychogalea fraenata) used to be one of the most common wallabies in eastern Australia, but today is one of Australia’s most critically endangered mammals. The only natural population of bridled nailtail wallabies is found at Taunton National Park (Scientific) in Central Queensland and the estimated population size is around 100 individuals (of approx. 500 in the early 1990’s). These 100 animals are concentrated in an area of about 1km2. After European settlement, the numbers of bridled nailtail wallabies declined rapidly and was thought to be extinct until a population was rediscovered in 1973 by a fencing contractor (Mr D. Challacombe). Mr Challacombe recognised the species after reading a Woman’s Day magazine article featuring rare and endangered species. This is clear evidence of the importance of public awareness of endangered wildlife, and that members of the community often have good idea of what animals are around. After the rediscovery of the bridled nailtail wallaby two cattle properties were bought and Taunton National Park (Scientific) was created for the protection of these animals.

The park is managed for the conservation of the bridled nailtail wallabies, however recently another environmental problem has made this management even more challenging. The problem isn’t actually new as it stems from the legacy of agricultural land management. The park was created from two cattle properties, where the high production grass species buffel grass (Cenchrus ciliaris L.) was introduced for pasture improvement. In the last 20 years, the abundance of buffel grass has increased and at the same time the distribution and number of bridled nailtail wallabies has decreased.

Bridled nailtail wallaby
Photo © Bluey Donaldson

Buffel grass is widely sown for cattle fodder in Central Queensland. It was introduced to improve pasture production and has proven to be fairly tolerant to disturbances such as grazing, droughts, and fire and it adapts easily to a wide range of conditions. Unfortunately all these attributes, which are beneficial to the cattle industry, make this grass difficult to stop from spreading and building up high populations in conservation areas. Buffel grass also imposes a much greater fire risk as it creates higher fuel loads which burn hotter and faster than most native grasses. This creates a problem, especially at Taunton National Park as the main vegetation feature in the bridled nailtail wallaby habitat is brigalow regrowth, a forest ecosystem which is fire sensitive and also critically endangered. Recent studies have also shown that buffel grass dominance reduces plant diversity by swamping and shading native pasture species. This is potentially a major issue for the bridled nailtail wallabies. Buffel grass has spread dramatically within the park and is now covering most of the open areas, especially in the area in which the bridled nailtail wallabies can be found. There are no cattle on the park and very few other grazing animals; therefore the fast-growing buffel grass has formed dense clumps of grass that are taller than 5 ft. In this research project, I am collecting data to quantify, for the first time, the impact buffel grass is having on endangered bridled nailtail wallabies.

To do this, I am using two approaches:

1. analysing past and present plant species composition with respect to bridled nailtail wallaby demography and distribution;
2. conducting an experiment to control buffel grass in clearings where bridled nailtail wallabies feed, as well as analyse the response of the grass and wallabies to two control treatments.

In the first part of this project, I am looking at the changes that happened at Taunton National Park over the last decades. I am especially focusing on the changes in distribution and habitat use of the bridled nailtail wallabies, as well as the vegetation biomass and plant composition. I will also collect detailed information on the individual animals by trapping wallabies to collect data on body size, body condition, parasite loads, and breeding success. I will use this information to assess the effect of buffel grass biomass on the health of wallabies, and measure changes in condition following vegetation manipulations.

Bridled nailtail wallaby
Photo © Bluey Donaldson

In order to find out about the habitat use of bridled nailtail wallabies today, I am using a combination of different methods. I am using GPS and VHF collars; the GPS collars record the movements of collared animals, whereas the VHF part enables me to follow them and track them whenever I need to find their current location. The collars give a good insight of the habitat use of the wallabies and help me collect information on any changes to habitat use and distribution before and after experimental reduction of buffel grass. These collars are a great way of collecting detailed information without disturbing the animals or changing their behaviour due to my presence. I am also monitoring wallaby habitat use and distribution using spotlighting and motion sensor camera traps. Camera traps deliver valuable information and interesting pictures of animals’ habitat use and behaviour collected without disturbing the animals. The combination of these methods is providing me with insight into how and when the wallabies use different parts of their habitats.

Thus far my results indicate that the parts of the park most heavily infested by buffel grass are being used less by the wallabies or completely avoided.

In the second part of my project I will experimentally change the habitat by controlling the buffel grass in some areas. I will control buffel grass by burning and slashing and monitor the response of the bridled nailtail wallabies and changes in pasture composition and biomass to the different control treatments. Burning has been used historically on the park as wildfire protection and slashing will simulate grazing. Grazing has to be simulated as Taunton is a National Park and grazing is not permitted. However, due to its history of being former cattle properties on which bridled nailtail wallabies could be found, the reintroduction of cattle to control the buffel grass might be a promising control strategy, but this strategy is highly controversial in Australia.

My PhD research is designed to provide more information on how and where buffel grass should be controlled at Taunton National Park (Scientific) in order to maximise habitat quality, population density, and population growth of the last remaining population of wild bridled nailtail wallabies. I will also help by collecting detailed information on the effects of buffel grass manipulation on the pasture composition and responding habitat use of the wallabies to help optimise future park management. The population of bridled nailtail wallabies at Taunton National Park (Scientific) has declined over 95% in abundance and range over the last 30 years, this decline needs to end and begin to increase.