Carcass use by mesoscavengers varied across modified landscapes in the absence of top carnivores

Abstract

The decomposition of carrion is crucial to the functioning and nutrient cycling of ecosystems, and many species use this high-quality resource. However, the availability and reliability of carrion differs across environments. Modified landscapes, such as farms and roads, often produce a high density of carcasses, with disproportionate benefits for generalist mesoscavengers that can tolerate, or are attracted to, human presence. In this study, we placed carcasses strategically across two large islands in southern Australia and used camera traps to investigate how different scavengers locate and use carrion in forested, farmland and roadside habitats. Forest ravens, an avian generalist, were the dominant scavengers across all three habitat types but were three times more likely to discover carcasses deployed in modified landscapes. Raptors were twice as likely to discover and use carcasses in farmland habitats, indicating enhanced scavenging opportunities in these areas. The discovery rate and use of carcasses by feral cats did not differ between habitat types. In this setting, differences in carrion use between diurnal and nocturnal scavengers are potentially due to the absence of top mammalian carnivores (Tasmanian devils and quolls). Diurnal scavengers, such as forest ravens and raptors, followed expected habitat preferences, albeit with greater access to carrion due to increased persistence. However, feral cats demonstrated no preference for carcasses across habitats, likely due to the reduced landscape of fear. Overall, our study underscores the important role of native mammalian carnivores in structuring scavenger communities and further validates the value of trophic rewilding to restore key ecological functions.

Keywords: Carcass use; Carrion; Feral cats; Land-use change; Scavenging.

Fig. 1

Geographic location of study sites across the Bass Strait Islands. The red indicators show the locations of King Island (left) and Flinders Island (right). Each black circle corresponds to a block. Within each block, we stratified the three habitat types (farm, road and forest) and placed a camera and a carcass at each site. The satellite image shows an example of a block, where three different sites of different habitats were selected in close proximity to one another

Fig. 2

Time series of the proportion of carcasses persisting in the environment across habitat types. Colour shading indicates the 95% confidence interval

Fig. 3

Kaplan–Meir estimates of the survival function for the proportion of carcasses discovered by a all species, b forest ravens, c raptors, and d feral cats across the three habitats. The 95% confidence interval is indicated by the shading

Fig. 4

Carcass consumption by focal species across the three habitat types. The proportion of total carcasses foraged by a forest ravens, b all raptors and c feral cats. The value for each site is indicated by the black dots and the error bars are bootstrapped 95% confidence intervals

Fig. 5

The average proportion of total scavenging time by forest ravens across the three habitat types. The values for each site are indicated by the black dots and the error bars are bootstrapped 95% confidence intervals