AIM

The effects of fires on vertebrate scavengers have not been characterised despite the importance of scavenging in shaping food web dynamics. We assessed whether the 2019/2020 megafires in Australia shifted the species richness, carcass detection, and feeding times of vertebrate scavengers, and whether the fire affected carcasses persistence times.

LOCATION

Blue Mountains, south-eastern Australia.

METHOD

We monitored vertebrate scavengers via remote cameras on a total of 60 experimentally placed kangaroo carcasses for 30 days in two periods before the megafire (January 2018 and 2019) and one period after the megafire (March 2020) in both open and closed canopy habitats. We compared vertebrate species richness, carcass discovery and scavenging activity before and after the fire and between the two habitats. We also assessed carcass persistence (time to carcass removal) before and after the fire and between the two habitats.

RESULTS

We collected more than 689,000 images of nine vertebrate scavengers including six avian, two mammal, and one reptile species. We detected no decline in scavenger species richness following the fire, and rates of carcass detection for mammals and reptiles did not differ across pre- and post-fire periods. On the other hand, avian scavengers detected carcasses faster in the post-fire period and in open compared to closed canopy habitats. Overall, scavengers increased their feeding times in the post-fire period, especially avian scavengers, but carcasses persisted longer in the post-fire period when compared to the second pre-fire period.

MAIN CONCLUSION

Our study identified that a widespread fire could influence avian scavenging dynamics, but that other factors affected carcass persistence times over the study period. Future monitoring of carcasses following fires should focus on the responses by both vertebrate and insect scavengers to fully elucidate the effects of these major disturbance events on critical ecosystem processes linked to decomposition.

Data collection

Our study was conducted in the Wolgan Valley in the Blue Mountains, south-eastern New South Wales. Carcass monitoring was conducted over three 1-month periods in the warm seasons of summer and autumn. The first two monitoring periods were conducted before a fire, in January 2018 and 2019, and the third was conducted in March of 2020. During each monitoring period, we distributed 20 adult eastern grey kangaroo carcasses in an equal mix of open grassland (hereafter “open canopy”; n=10 sites) and forest (hereafter “closed canopy”; n=10 sites) habitat. Open canopy sites were at least 50 m from any stands of trees. The closed canopy sites had more than 20% canopy cover before the fire, and in the post-fire period carcasses were placed in forested locations where there was previously canopy cover of more than 20%. Within monitoring periods, carcasses were separated by at least 1 km to mitigate scent travel between carcasses. Between monitoring periods, however, carcasses were positioned at least 100 m from any previous carcass placement. We used dead kangaroos sourced from nearby management culls, so no animals were killed for the purpose of this study. Any carcass displaying evidence of disease (e.g. heavy parasite loads) was not used. All carcasses were placed into the field without freezing within 24 hours of collection (i.e. all at the same time, with 24 hours being the longest time between the first and last carcass placement; January 2018; 9:00 – 23:00, January 2019; 8:00 – 13:00, and March 2020; 23:00 – 6:00). Scientific licenses/permits were obtained to relocate the kangaroo carcasses (SL 101901) and research was approved by the University of Sydney Animal Ethics Committee (Project number: 2017/1173).

To allow for ongoing monitoring and detection of scavengers visiting and feeding on each carcass, we used a Reconyx PC800 Hyperfire™ camera trap (Professional Reconyx Inc., Holmen, WI, USA) attached to a free-standing star picket 3–4 m away from each carcass. The cameras were programmed to take continuous photographs when triggered by thermal movement around the carcass (rapidfire, no wait period). To prevent complete removal of the carcasses from the remote camera monitoring frame, we secured carcasses to the ground by wire attaching the neck and achilles tendon of the animal to two metal stakes spaced ~0.6 m apart. Cameras were used to monitor carcasses for 30 days to capture the main period of vertebrate scavenging activity and because the majority of carcass biomass (including meat, skin and bones) were removed from the environment in this time.

Data processing

Camera images were tagged according to each new carcass visitation event by a different species, the number of individuals of a species present, whether any of the individual species fed on the carcass or not, and the date and time that the observation was recorded. A visitation event was considered new if it occurred ≥ 10 min from the previous visitation event by the same species. We defined scavenger species as species that were observed feeding on at least one carcass over the three study periods. All other animals captured on the remote cameras were excluded from our analyses. Finally, using a combination of in-person visual inspection of the carcasses and inspection of camera images, we determined the number of days until complete carcass consumption. A carcass was defined as completely consumed when less than 5% meat biomass and only skin, hair and/or bone remained.

Each dataset (tab) used for the main statistical analysis in the related paper have been uploaded. Some notes are provided in each tab.