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Carrion use by a reptile is influenced by season, habitat, and competition with an apex mammalian scavenger

Cite this dataset

Cairncross, Rhys (2024). Carrion use by a reptile is influenced by season, habitat, and competition with an apex mammalian scavenger [Dataset]. Dryad. https://doi.org/10.5061/dryad.0p2ngf28m

Abstract

Scavenging on carrion is critical and often fiercely competitive for a range of vertebrate species, from native apex predators to invasive species and even reptiles. In Australia, a notable reptilian scavenger is the lace monitor (Varanus varius). In this study, we quantified lace monitor activity at carcasses and compared their use of the resource to common co-occurring predators that also scavenge; the invasive red fox (Vulpes vulpes), and native apex predator, the dingo (Canis dingo). To do so, we deployed 80 macropod carcasses equally across seasons (summer and winter) and habitats (open and closed canopy), in a temperate bioregion and monitored vertebrate scavenging with camera traps. Lace monitor activity was 1.67-times higher in summer than winter, but it did not differ across closed and open habitats. Monitor activity occurred earlier after carcass deployment at sites deployed in summer than winter (1.47-fold earlier), and at carcasses in open than closed habitats (0.22-fold earlier). Lace monitors initially discovered carcass sites faster in summer than winter and before both red foxes and dingoes in summer. Lace monitors were active diurnally in both summer and winter, differing from the red fox, which was strictly a nocturnal scavenger, and the dingo, which was significantly more active at night across both seasons. Finally, we found that lace monitor activity at carcass sites decreased slightly with higher rates of activity for dingoes (0.04-fold decrease as dingo activity increased), but not with red fox activity. Our results have implications for understanding lace monitor foraging and scavenging and highlight the value of monitoring carcasses to provide important insights into the behaviour of varanid lizards that scavenge.

README: Carrion use by a reptile is influenced by season, habitat, and competition with an apex mammalian scavenger

https://doi.org/10.5061/dryad.0p2ngf28m

The dataset contains cleaned data that was utilised to analyse trends in the activity at carcasses of lace monitors (Varanus varius), a reptilian scavenger, across seasons and habitats. It also contains data concerning the two main competitor predators that also scavenged, the dingo (Canis dingo) and red fox (Vulpes vulpes).

Description of the data and file structure

The first sheet in this dataset 'All.data' contains all the event data across the three species of study: red foxes, dingoes, and lace monitors. This was used to determine the average times visiting carcass sites for each species across both seasons of study (summer and winter) and informed the bootstrapping used to determine 95% confidence intervals for this. The columns also include additional data, namely the group size recorded in each event (Group.size column), the time since carcass deployment in days (Time.since column), the camera station that each carcass was monitored at (Station column), the deployment period (Period column, numbered 0, 1, 3 and 4 in order of first to last), the habitat that each event occurred in (habitat column, open or closed), the start (Mintime column) and end (Maxtime column) time for each event and the day that carcasses were first deployed at each station within each deployment period (Deploy.time column). The season column dictates what season each event occurred in and the species column what species were recorded in each event.

The second sheet 'Lace.monitor.data' is derived from the 'All.data' sheet but is filtered to only include lace monitors. This data was used to determine what day lace monitors visited carcasses, across seasons and habitats, after we had initially deployed them in the field. The columns remain the same as described for the 'All.data' sheet.

The third sheet 'Arrival.data' contains time to first arrival across the three species, as well as seasons and habitat, for each carcass monitoring station within each deployment period. This data is formatted for a Cox-proportional Hazards survival analysis. The Event column indicates whether a carcass at any independent monitoring station for one of the deployment periods was located by one of the three species of interest. A value of 1 indicates that it was discovered within 30 days and a value of 0 indicates it was not. The Time.since column indicates the time (days) that carcasses were discovered. All other columns remain the same as described for the 'All.data' sheet.

The fourth sheet 'Dingo.fox.monitor' contains the summarised dingo (Dingo column) and red fox (Red fox column) event data alongside that of lace monitors (Lace monitor column). Data were summarised such that the total number of independent events at carcasses were reported for each species. This data includes dingo and red fox events at carcass sites where lace monitors occurred. This data was used to first determine how lace monitor activity at carcasses differed between seasons and habitats. Next, it was then used to assess how dingoes and red foxes influenced lace monitors at carcasses. All other columns remain the same as described for the 'All.data' sheet.

The fifth sheet 'Appendix' contains biomass removal data contributed to by dingoes and red foxes across a subset of the entire dataset (two carcass deployment periods, one in winter and one in summer). The Biomass column indicates the amount of weight removed from the carcasses (in kilograms). The Dingo and Red fox columns indicate the total events recorded at each carcass monitoring station for both species, respectively. The Total column indicates the sum of both red fox and dingo events at each station. The other columns remain the same as described for the 'All.data' sheet.

Methods

This dataset was collated by placing 80 eastern grey kangaroos (Macropus giganteus) carcasses within open and closed habitats and winter and summer seasons over four independent sampling periods (n = 20 in each deployment period, n = 10 in open and closed habitats in each deployment period). The study area was the Wolgan Valley in the west of the Sydney Basin Bioregion, NSW, Australia. Carcasses were monitored with camera traps and all scavengers recorded were identified using the program Digikam. We then used the package 'camtrapR' within R to extract the tagged images and created independent 'events' for each species occurrence. These events were classified as when an animal entered the frame of the camera and ended when the animal left the frame. Unique events were considered to be when more than ten minutes elapsed between events of the same species or when a different species entered the camera frame within 10 minutes of another. We then filtered this dataset to only include lace monitors, red foxes, and dingoes. Carcass sites were monitored for 30 days continuously.

Funding

Paddy Pallin Foundation

Ecological Society of Australia

Royal Zoological Society of New South Wales