SREL Reprint #3713

Scavenging dynamics on Guam and implications for invasive species management

Jacob E. Hill1, Kelsey L. Turner1, Joshua B. Smith1, Matthew T. Hamilton1, Travis L. DeVault1,
William C. Pitt2, James C. Beasley3, and Olin E. Rhodes Jr.4

1Savannah River Ecology Laboratory, University of Georgia, Aiken, SC, USA
2Smithsonian Conservation Biology Institute, Smithsonian Institution, Front Royal, VA, USA
3Savannah River Ecology Laboratory, Warnell School of Forestry and Natural Resources,
University of Georgia, Aiken, SC, USA
4Savannah River Ecology Laboratory, Odum School of Ecology, University of Georgia, Aiken, SC, USA

Abstract: Deployment of mouse carcasses laced with acetaminophen has become a common management tool to control invasive brown tree snakes (Boiga irregularis; BTS) on Guam. Additionally, anticoagulant rodenticides may be used to control invasive rats (Rattus spp.) if their populations increase due to predator release in the wake of BTS eradication. However, there has been little research examining how scavengers on Guam could be incidentally exposed to toxicants by scavenging carcasses of animals that die from these population control strategies. Furthermore, there is a limited understanding of how the proliferation of invasive species on Guam has influenced the composition of the scavenger community. We investigated these topics by examining scavenger consumption of mouse, rat, and BTS carcasses on Guam in both a coastal and upland site during the wet (May–Aug 2016) and dry season (Jan–Apr 2017). We documented carcass consumption by 9 species, which scavenged 48% of carcasses. Interactions between season, habitat, and carcass type influenced probability of scavenging, and appeared to be driven by consumption by the two main scavenger species, BTS and cane toads (Rhinella marina), both of which are invasive on Guam. Baiting programs should consider the potential for toxin exposure to land crabs (Coenobita spp., Birgus latro), native species that scavenged at every combination of carcass type, habitat, and season. Overall, 60% of scavenging events were attributed to species considered pests that are recent introductions to Guam. Invasive species on Guam are the primary scavengers of small vertebrate carrion, suggesting a substantial role in trophic dynamics that extends beyond predation.

Keywords: Brown tree snake, Cane toad, Scavenging ecology, Carrion

SREL Reprint #3713

Hill, J. E., K. L. Turner, J. B. Smith, M. T. Hamilton, T. L. DeVault, W. C. Pitt, J. C. Beasley, and O. E. Rhodes Jr. 2023. Scavenging dynamics on Guam and implications for invasive species management. Biol Invasions 25: 1845-1858.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).