Carcasses attract invasive species and increase artificial nest predation in a desert environment

1. Global road networks facilitate habitat modification and are integral to human expansion. Many animals, particularly scavengers, use roads as they provide a reliable source of food, such as carrion left after vehicle collisions. Tasmania is often cited as the 'roadkill capital of Australia', with the isolated offshore islands in the Bass Strait experiencing similar, if not higher, levels of roadkill. However, native mammalian predators on the islands are extirpated, meaning the remaining scavengers are likely to experience lower interference competition.2. In this study, we used a naturally occurring experiment to examine how the loss of mammalian carnivores within a community impacts roadside foraging behaviour by avian scavengers.3. We monitored the locations of roadkill and forest ravens Corvus tasmanicus, an abundant scavenger species, on eight road transects across the Tasmanian mainland (high scavenging competition) and the Bass Strait islands (low scavenging competition). We represented raven observations as one-dimensional point patterns, using hierarchical Bayesian models to investigate the dependence of raven spatial intensity on habitat, season, distance to roadkill and route location. 4. We found that roadkill carcasses were a strong predictor of raven presence along road networks. The effect of roadkill was amplified on roads on the Bass Strait islands, where roadside carrion was a predictor of raven presence across the entire year. In contrast, ravens were more often associated with roadkill on Tasmanian mainland roads in the autumn, when other resources were low. This suggests that in the absence of competing mammalian scavengers, ravens choose to feed on roadside carrion throughout the year, even in seasons when other resources are available. This lack of competition could be disproportionately benefiting forest ravens, leading to augmented raven populations and changes to the vertebrate community structure. 5.Our study provides evidence that scavengers modify their behaviour in response to reduced scavenger species diversity, potentially triggering trophic shifts and highlighting the importance of conserving or reintroducing carnivores within ecosystems.

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“…In the Simpson Desert, Australia, the presence and proximity of carcasses to nests increased predation by corvids (Spencer et al, 2021).…”

Section: F I G U R Ementioning

confidence: 99%

Roadkill islands: Carnivore extinction shifts seasonal use of roadside carrion by generalist avian scavenger

Fielding

Buettel

Brook

et al. 2021

Journal of Animal Ecology

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“…Until recently, cats were believed to rarely scavenge [36, 37]. However, there is now a growing body of evidence that they actively scavenge, especially when they perceive little risk [41]. Our data show that in the simple scavenger community, feral cats scavenged at eight times the rate of cats living in a full scavenger community (Fig.…”

Section: Discussionmentioning

confidence: 77%

“…Further research is needed to confirm whether these species are truly increasing in abundance. Elevated numbers of forest ravens could have destructive effects for the local birds on the islands through heightened levels of depredation, and impact local farmers through increased attacks on livestock, as shown in other corvid studies [41, 50], as well as on King Island specifically [51]. While past research in Tasmania found no impact of forest raven abundance on the abundance of other bird species [52], these impacts may differ on the Bass Strait islands if the raven population size is greater.…”

Section: Discussionmentioning

confidence: 87%

Dominant carnivore loss benefits native avian and invasive mammalian scavengers

Fielding¹,

Cunningham²,

Buettel³

et al. 2021

Preprint

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Scavenging by large carnivores is integral for ecosystem functioning by limiting the build-up of carrion and facilitating widespread energy flows. However, top carnivores have declined across the world, triggering trophic shifts within ecosystems. In this study, we use a natural 'removal experiment' of disease-driven decline and island extirpation of native mammalian (marsupial) carnivores to investigate top-down control on utilisation of experimentally placed carcasses by two mesoscavengers - the invasive feral cat and native forest raven. Ravens were the main beneficiary of carnivore loss, scavenging for five times longer in the absence of native mammalian carnivores. Cats scavenged on almost half of all carcasses in the region without dominant native carnivores. This was eight times more than in areas where other carnivores were at high densities. In the absence of native mammalian carnivores, all carcasses persisted in the environment for 3 weeks. Our results reveal the efficiency of carrion consumption by mammalian scavengers. These services are not readily replaced by less-efficient facultative scavengers. This demonstrates the significance of global carnivore conservation and supports novel management approaches, such as rewilding in areas where the natural suite of carnivores is missing.

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“…2015; Spencer et al . 2021). It is possible that in the spring following the flood, carrion was an important food subsidy for corvids that maintained their population in the area, as seen in other scavengers (Newsome et al .…”

Section: Discussionmentioning

confidence: 99%

Effects of habitat, season and flood on corvid scavenging dynamics in Central Australia

et al. 2022

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Carrion is an ubiquitous resource that drives the dynamics of scavenger populations and shapes the structure and composition of their communities. Corvids (Family: Corvidae) are among the most common scavengers globally, facilitating carcass discovery by other species and contributing to carcass biomass removal. Here, we examine how environmental factors influence corvid scavenging dynamics in an arid region of Central Australia. Specifically, we investigate how habitat, season and a major flood event affect corvid discovery and visitation time, and group size around carcass sites. To do so, we used data collected from camera traps monitoring 80 experimentally positioned red kangaroo (Osphranter rufus) carcasses stratified across closed and open habitats, spring and winter seasons, and before and after a flood event. Corvids took longer to discover carcasses in closed compared to open habitats, but habitat did not affect how long corvids spent visiting carcasses, or corvid group size. Corvids discovered carcasses faster in winter compared to spring and in post-flood compared with the preflood periods, and season and flood interacted to influence both corvid visitation time and group size. Our results reflect a complex interplay between temperature, the extreme boom and bust cyclicity of the study region and changing corvid activity and abundance in the local study area. We identify environmental factors as key determinants of corvid scavenging dynamics and provide the first detailed description of scavenging by corvids in the arid zone of Australia.

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Carcasses attract invasive species and increase artificial nest predation in a desert environment

Cited by 17 publications

References 50 publications

Roadkill islands: Carnivore extinction shifts seasonal use of roadside carrion by generalist avian scavenger

Roadkill islands: Carnivore extinction shifts seasonal use of roadside carrion by generalist avian scavenger

Dominant carnivore loss benefits native avian and invasive mammalian scavengers

Effects of habitat, season and flood on corvid scavenging dynamics in Central Australia

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