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

Abstract

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.

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

“…Together, these species accounted for 88% of all recorded events. The scavenging rates observed by ravens were not unusual, with many studies both within Australia and globally describing raven species as prolific scavengers (Selva et al 2003;O'Brien et al 2010a;Mateo-Tomás et al 2015;Bragato et al 2022;Newsome and Spencer 2022). However, the brushtail possum has received little recognition as a regular scavenger (but see Brown et al 1993;Heinsohn and Barker 2006;O'Brien et al 2010b).…”

“…same species (methods as per Bragato et al 2022;Newsome and Spencer 2022). Only species-specific events could be characterised because identification of individuals for most species was not possible.…”

Habitat but not group size or recent predator activity affect corvid collective vigilance at carcasses

“…The increase in vigilance levels of corvids in open compared with closed habitat, although unexpected, could be due to several factors. First, during the study period predator activity and corvid activity were both greater in open habitat, probably because carcasses are found more quickly in open than in closed habitat (Bragato et al, 2022; Spencer & Newsome, 2021). Elevated activity in open habitat could potentially lead to more frequent encounters between predators and prey, and larger scavengers are likely to exclude corvids from carcasses to monopolize the valuable resource.…”

“…Each carcass was monitored for 3 months, and the first 30 days of monitoring data were used to test our predictions. This encapsulated the period when vertebrate scavengers, especially corvids, were most active on carcasses (Bragato et al, 2022); red kangaroo carcasses in the study area take an average of 14 days to decompose (Spencer & Newsome, 2021).…”

“…The increase in vigilance levels of corvids in open compared with closed habitat, although unexpected, could be due to several factors. First, during the study period predator activity and corvid activity were both greater in open habitat, probably because carcasses are found more quickly in open than in closed habitat (Bragato et al, 2022;Spencer & Newsome, 2021).…”