Carcass use by mesoscavengers drives seasonal shifts in Australian alpine scavenging dynamics

Abstract

Context.Carrion is a high-energy and nutrient-rich resource that attracts a diverse group of vertebrate scavengers. However, despite the carrion pool being highly seasonal in its availability, there is little understanding of how scavengers utilise carcasses across all four seasons. Aim. To assess how season influences carcass-detection times by vertebrate scavengers and their rates of scavenging. Methods. We used remote cameras to monitor vertebrate scavenging at 15 eastern grey kangaroo (Macropus giganteus) carcasses in four consecutive seasons (summer, autumn, winter, and spring; total 58 carcasses) in the Australian Alps. Key results. In total, 745 599 remote-camera images were captured, within which 34 vertebrate species were identified, nine of which were recorded to actively scavenge. Time to first detection of carcasses by vertebrate scavengers was 5.3 and 9.6 times longer during summer (average 144 h) than during spring (average 34 h) and winter (average 24 h) respectively. Rates of vertebrate scavenging were highest in winter and spring, with brushtail possums (Trichosurus vulpecula) accounting for 78% of all scavenging events during winter, and ravens (Corvus spp.) accounting for 73% during spring. High rates of carcass use by these mesoscavengers may reflect a scarcity of other food sources, the demands of their breeding season, or a relative absence of scavenging by larger dominant species such as dingoes (Canis dingo) and wedge-tailed eagles (Aquila audax). Conclusions. These findings demonstrate the highly seasonal nature of vertebrate scavenging dynamics in an alpine ecosystem, and that mesoscavengers, not apex scavengers, can dominate the use of carcasses. Implications. Accounting for the effects of season is integral to understanding the way animals utilise carcasses in alpine and other strongly seasonal environments; and for developing further our knowledge of ecosystem processes linked to decomposition.

Squamate scavenging services: Heath goannas (Varanus rosenbergi) support carcass removal and may suppress agriculturally damaging blowflies

“…This is consistent with other scavenging studies that have occurred within the range of the heath goanna (O'Brien et al., 2007 ), but contrasts with studies elsewhere in Australia which have recorded minimal scavenging activity by squamate reptiles even during summer months (e.g. Newsome & Spencer, 2022 ; Read & Wilson, 2004 ; Vandersteen et al., 2023 ). This suggests that heath goannas play a particularly important role as scavengers on the south coast of Australia relative to squamates elsewhere on the continent.…”

“…Previous studies have used large mammal carcasses (typically kangaroos) (e.g. Newsome & Spencer, 2022 ; Read & Wilson, 2004 ; Vandersteen et al., 2023 ), whereas in this study we make use of smaller carcasses (rats). The use of relatively small carcasses allowed us to carry out experiments across many sites, providing us with large sample sizes and allowing us to account for spatial variability within landscape treatments.…”

“…The relative contribution of different taxa to scavenging ecosystem functions is highly seasonally variable in Australia (Bragato et al., 2022 ; Read & Wilson, 2004 ; Vandersteen et al., 2023 ). We carried out this study in early and late summer, when heath goannas undertake most active foraging (Rismiller et al., 2010 ).…”

“…This allowed us to assess the maximum potential contribution of heath goannas to scavenging ecosystem functions. We would expect scavenging rates to change throughout the year, with a drop in relative contribution of heath goannas in winter, as their activity levels drop but other species increase reliance on carrion food sources (DeVault et al., 2011 ; Sawyer et al., 2022 ; Vandersteen et al., 2023 ). Future studies should investigate the seasonal variability in scavenging activity in coastal mallee ecosystems.…”

“…In Australia, scavenging is primarily undertaken by corvids (Bragato et al., 2022 ; Peisley et al., 2017 ; Read & Wilson, 2004 ), native marsupials (Cunningham et al., 2018 ; Vandersteen et al., 2023 ), introduced and naturalized mammalian carnivores (Newsome & Spencer, 2022 ; Spencer & Newsome, 2021 ; Vandersteen et al., 2023 ; Wirsing & Newsome, 2021 ), and specialist invertebrates (Read & Wilson, 2004 ). The relative contribution of different groups to scavenging is highly dependent on season and habitat type (Bragato et al., 2022 ; Read & Wilson, 2004 ; Vandersteen et al., 2023 ) and exclusion of mesoscavengers by larger species (Cunningham et al., 2018 ; Vandersteen et al., 2023 ). No studies have formally investigated the contribution of squamate reptiles to scavenging ecosystem functions in Australia, with most vertebrate studies focused on mammals and birds (Barton et al., 2013 ).…”