We've all driven our rural and peri-urban highways and seen the carnage of roadkill often being picked over by a cast of hawks, a murder of crows or the occasional Wedge-tailed Eagle. The fast-slow driving that accompanies the dodging of these hungry birds punctuates long trips in the outback.
Natural or man-made carrion is a typical component of the landscape, and many species across many continents are specialised to eat this resource. There are suites of vultures that specialise in eating different components of the carcass (from the flesh to the bones), and in Africa, hyenas are bone eaters with a certain spiritual reverence in some areas (for example the gey waraba of Ethiopia). Even in Australia, the Tasmanian Devil, with their massive maws are marrow mashers.
But have you ever stopped to think, how does this provision of resources in the landscape affect wildlife patterns in general?
If you add a heap of additional unexpected food resources, what then happens to the array of carrion eaters and predators, and how does this affect other smaller animals?
While surprisingly understudied in Australia, this question has been pondered in detail by Emma Spencer, a PhD student with the University of Sydney. More specifically, she has thought about this with respect to our native Dingo population and introduced feral cats.
Dingoes are opportunist predators and typical carrion eaters, whereas feral cats tend to focus on small live prey, even as this prey becomes scarce in the environment. The highly selective and efficient feeding habits of feral cats is a big problem and have been linked to the range reduction and extinction of vulnerable small animals across Australia, particularly in the country’s more arid environments.
Hope is not yet lost however, and there's now a growing body of research investigating the role of different-sized predators in suppressing each other. In Australia, the reduction or increase of Dingo populations has been linked to release of pressure on or suppression of feral cats. So, if Dingos kill or exclude cats, then the small animals that cats eat will be protected.
The key question is then – how can we keep Dingoes on our reserves to act as native animal guardians?
During the drought, feral cats persist, while Dingoes tend to drop off earlier. Perhaps the provision of food, via carrion (e.g. from roadkill) can help maintain Dingo numbers. And, by increasing Dingo activity, predation of feral cats by Dingoes could be increased. Then species that are particularly vulnerable to the cat predation – such as Night Parrots nesting at Bush Heritage's Pullen Pullen Reserve in western Queensland – might be protected.
Emma’s research is testing this hypothesis and specific questions such as:
- How does carrion provisioning encourage Dingo movement and abundance?
- How do cats change their ranging behaviour in response to a temporary increase in Dingo activity?
- What other scavengers use carrion, and how does this effect soil, invertebrate and plant communities?
- And are there any unintended consequences, such as a heightened predation on nests and eggs in the vicinity by dingos or other species?
The conservation management outcomes for Bush Heritage through the protection of our native and threatened species could be substantial.
We sometimes undertake feral herbivore control activities (e.g. of camels), as part of our reserve management, and doing this strategically so as to enhance Dingo activity and suppress cat activity could be an easy way to manipulate the environment for the best conservation outcomes.
On the other hand, and perhaps equally as important, if it's found that placing carcasses for cat control purposes has certain unintended, negative effects, then such findings will enable us to direct future control practices in order to minimise or eliminate these impacts.
In June, Emma began the first part of her study, based at Ethabuka Reserve, by setting up 20 carrion sites, a range of cameras, and artificial nests to determine what visits the carrion and the surrounding areas and to test the potential impacts of carrion on nesting success. We'll report the outcomes via subsequent blog posts soon – so stay tuned!
Emma’s project is supported by the Australian Government National Environmental Science Program's Threatened Species Recovery Hub and by Bush Heritage and all our generous supporters and donors.