By restoring these ecosystem processes and species interactions, the goal is to promote complexity and self-sustaining ecosystems. So, what can we do about this? Well, one important answer could be trophic rewilding – the restoration of ecological function through the introduction of targeted animal species. The local farmers are also disadvantaged, as an overabundance of ravens leads to heightened attacks on livestock, such as sick or newborn lambs. This is bad news for the many threatened birds on the islands with nest depredation by ravens on the rise. On the Bass Strait islands, the lack of competition for roadkill could be disproportionately benefiting forest ravens, explaining the apparent increase in raven abundance across the islands. The loss of apex predators within ecosystems has been found to trigger increases in the abundance of smaller predators (meso-predator release), leading to greater hunting pressure on smaller prey. A pair of forest ravens feeding on a wallaby carcass on King Island (Credit: Matthew Fielding). This suggests that under lower levels of competition, ravens can, and choose to, feed on roadkill throughout the year, even in seasons when other resources are readily available. In contrast, ravens were mostly clustering around roadkill on Tasmanian mainland roads in the autumn, when other resources were low. However, the effect of roadkill was greater on the Bass Strait islands, where ravens used the resource heavily throughout the entire year.
Unsurprisingly, we found that roadkill was a strong predictor of raven presence along roads in general. We monitored the locations of roadkill and ravens on eight road transects across four seasons on the Tasmanian mainland and the Bass Strait islands. In our recent paper in the Journal of Animal Ecology, we used this naturally occurring experiment to examine how the loss of native carnivores, like the devil and quoll, within a community impacts the use of roadkill by a remaining scavenger, the forest raven. So, what happens when we lose the main scavenger in an environment? Does this impact the foraging behaviour of the remaining scavengers? The Tasmanian devil is the apex scavenger across the Tasmanian mainland (Credit: JJ Harrison ( ), CC BY-SA 3.0, via Wikimedia Commons) With no great competition for carcasses, the two species are left with a smorgasbord of roadkill to feed on. There are now two main scavengers remaining on the islands, the feral cat ( Felis catus), an invasive carnivore, and the forest raven ( Corvus tasmanicus), a native omnivore. However, on the Bass Strait islands, these native mammalian predators are absent, either due to historical extermination by European settlers or past processes that we are yet to understand (e.g., the devil has only been found in the recent fossil record on Flinders Island). In Tasmania, carcasses, like roadkill, are often quickly munched down by apex scavengers like the Tasmanian devil ( Sarcophilus harrisii) and meso-predators, like the spotted-tailed quoll ( Dasyurus maculatus). The extensive open pastures across the islands have resulted in incredibly high numbers of macropods (wallabies and pademelons), meaning vehicle-animal collisions are often difficult to avoid. The two largest islands in the region, King Island and Flinders Island, have been heavily modified for cattle and sheep farming. Tasmania, a large island off the southeast of Australia, is often regarded as the ‘roadkill capital of Australia’ however, the offshore Bass Strait islands could arguably steal that title. (Credit: JJ Harrison ( ), CC BY-SA 3.0, via Wikimedia Commons) A forest raven (Corvus tasmanicus), a common scavenger, feeds on roadkill in Tasmania. Scavengers will often exploit these resources, using roads as a regular food source.
Yet, roadsides often provide a reliable source of animal carcasses from vehicle-animal collisions, commonly known as roadkill. In the natural environment, carrion is often scarce and difficult to locate. However, some animals do benefit from our growing network of roads.
When we think of roads and animals, we are often plagued with negative thoughts – roadkill, fragmentation, pollution. He is passionate about the conservation of bird species and is particularly interested in how humans impact bird communities. A self-confessed “bird nerd”, you can usually find him in the Tasmanian wilderness behind a pair of binoculars. Matthew Fielding is a PhD student at the School of Natural Sciences at UTAS. This blog post is provided by Matthew Fielding and tells the #StoryBehindThePaper for the paper ‘ Roadkill islands: Carnivore extinction shifts seasonal use of roadside carrion by generalist avian scavenger’, which was recently published in the Journal of Animal Ecology.
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