Carrion is a valuable nutrient resource in the environment that is used by a diversity of organisms encompassing all biological kingdoms. Due to the low cost of energy derived from carrion, most vertebrate species are facultative scavengers, and thus provide a critical ecosystem service for humans and other organisms by removing decaying animal matter from the environment. In fact, a surprising array of animals will forage on carrion, including eagles, white-tailed deer (Odocoileus virginianus), and many species of snakes and lizards. However, despite the importance of scavenging for ecosystem health, many knowledge gaps still exist regarding the diversity and function of scavenger communities. In addition, while it is accepted that carcass size and location can influence the diversity and composition of scavenging communities, there is little research to support this assertion. In particular, scavenging research in human-disturbed landscapes is lacking as most studies have been conducted in relatively pristine environments with intact scavenger communities. Thus, there is a critical need to study scavengers in ecosystems that have been dramatically altered by anthropogenic land use. 

coyotes feeding on pig carcass

THE EFFECTS OF CARCASS SIZE, HABITAT TYPE, AND SEASON ON SCAVENGING COMMUNITIES IN THE SOUTHEAST

SREL Collaborators: Jim Beasley, Kelsey Turner, Erin Abernethy, Gene Rhodes

It is generally accepted that carcass size and location influence scavenging communities, yet there is little research supporting this notion. To date, most scavenging research has focused on a single carcass size or type, resulting in an oversimplified understanding of scavenging dynamics. Similarly, despite the fact that species composition often is greatly influenced by habitat and anthropogenic land use, few studies have taken a multi-habitat approach or incorporated human-impacted landscapes in scavenging studies. This study aims to fill these critical gaps by examining the influence of a large gradient in carcass size (i.e. rat, rabbit, and wild pig) as well as a diversity of habitat types (i.e. hardwood, clearcut, immature pine, and mature pine) on the composition and efficiency of scavenging communities during two distinct seasons. This research is being conducted on the Savannah River Site and we are using no-glow infrared remote cameras to document scavenging of placed carcasses. From these data we plan to elucidate carcass detection rates, composition of scavenger communities, and carcass persistence as a function of carcass size, habitat type, and season to better understand nutrient cycling and scavenger dynamics in southeastern ecosystems. 

raccoon peering from behind a tree

THE EFFECT OF MESOPREDATOR AND IMPORTED RED FIRE ANT EXCLUSION ON VERTEBRATE SCAVENGING COMMUNITIES

SREL Collaborators: Jim Beasley, Kelsey Turner

Outside collaborators: Mike Connor (Jones Center)

Intact scavenging communities provide numerous ecosystem services as they play a critical role in disease dynamics, nutrient cycling and redistribution, and carcass removal. However, the addition (e.g., invasive species) or removal (e.g., extirpation) of scavengers from ecosystems can disrupt the efficiency and composition of scavenging communities. This imbalance not only interrupts the flow of energy in an ecosystem, but also may lead to increased health risks for people, livestock, and other wildlife (e.g. disease). For instance, the recent dramatic decline of vultures in Asia has led to increases in feral dog and rat populations, resulting in a significant increase in human rabies cases from dog bites, as well as diminished efficiency of carcass removal by the scavenging community as a whole. In collaboration with Dr. Mike Conner at the Joseph W. Jones Ecological Research Center, we are testing the effects of the exclusion of mammalian predators on carcass persistence and scavenger community composition. Although some previous studies have excluded individual scavenger species, this is the first study that will assess exclusion of an entire guild of scavengers. This will be done by conducting scavenging experiments in replicated ~100 acre mesopredator exclusion and control areas and monitoring carcass fate using remote cameras. In addition to excluding mammalian predators, we will also exclude red imported fire ants (Solenopsis invicta), believed to outcompete vertebrate scavengers for carrion resources, in separate experiments to determine the impact this invasive species is having on scavenger communities in the southeast.

EFFECTS OF ANTHROPOGENIC CONTAMINANTS ON COLEOPTERAN SCAVENGING ASSEMBLAGES

SREL Collaborators: Jim Beasley, Ansley Silva, Kelsey Turner, Erin Abernethy, Gene Rhodes

Outside Collaborators: Kamal Gandhi (UGA), David Coyle (UGA), Jeff Tomberlin (Texas A&M)

Trophic food webs directly influence ecosystem functions, such as energy flow and nutrient cycling, and decomposers play a major role in these processes because they feed at every level of the food web. Decomposing vertebrates represent a resource pulse that creates mass heterotrophic activity in a localized area. Some invertebrates are specialized in decomposition and their role in this process is important to food-web architecture: perhaps increasingly important due to trophic downgrading and the disappearance of top predators. Despite the importance of invertebrate scavengers to food webs, little is known about how specific disturbances —e.g., contamination by radioactive pollution and metals—affect their assemblages. Generally, invertebrates of the Order Coleoptera are known bioindicators of ecosystem health and some beetles specialize in decomposition. This study will monitor insect assemblages linked to nutrient cycling and the decomposition of carrion at both contaminated and uncontaminated sites on the Savannah River Site. Since environmental disturbances can alter community dynamics, we will investigate whether soils contaminated with metals and radionuclides lead to shifts in scavenging insect community composition and structure, with a focus on coleopteran species.

brown tree snake in gloved hand

INDIRECT TRANSFER OF TOXICANTS TO NON-TARGET ORGANISMS VIA SCAVENGING PATHWAYS ON GUAM

SREL Collaborators: Gene Rhodes, Jim Beasley, Josh Smith, Kelsey Turner

Outside Collaborators: Travis DeVault (APHIS), Will Pitt (SCBI)

Brown tree snakes (BTS; Boiga irregularis) and rodents (i.e., rats and mice – Rattus spp. and Mus spp.) were inadvertently introduced to Guam and have negatively impacted both the economy and native fauna of this small Pacific island. BTS have been especially problematic given their propensity to survive in close proximity to human development, highly varied diet, and the fact that they are agile climbers that often seek shelter in cargo or transport vessels. These characteristics, coupled with Guam’s strategic position as a focal point for commercial and military shipments, present a significant threat of BTS dispersal to other areas. Current control efforts of BTS on Guam are focused on area-specific population reduction, rather than island-wide eradication. Primary methods of control include trapping, barriers, spotlighting, and prey-base control using rodenticides for rodents around cargo facilities. Recently, mass aerial delivery of dead mice baits treated with acetaminophen has been used to cost-effectively reduce BTS populations over larger areas. Widespread use of rodenticides and acetaminophen by federal organizations for management and conservation objectives may face challenges if the transfer rates and fates of these toxicants are not accounted for in risk assessment models. Consequently, our objectives are to:

1.   Determine the location of BTS carcasses following ingestion of acetaminophen to elucidate indirect transport of toxicants among trophic levels within the Guam ecosystem.

2.   Utilize experimental scavenging trials conducted with rodents and BTS carcasses to evaluate the diversity and efficiency of scavenger communities that utilize the carrion resulting from eradication efforts on Guam.

decomposing duck in invertebrate pitfall trap

INFLUENCE OF INVERTEBRATE SCAVENGERS ON THE FATE AND TRANSPORT OF 137CS WITHIN FOOD WEBS

SREL Collaborators: Jim Beasley, Chris Leaphart, Heaven Tharp

Outside Collaborators: Jeff Tomberlin (Texas A&M)

Due to nuclear weapons testing, nuclear accidents, and other anthropogenic inputs, radionuclides have been dispersed across many ecosystems around the world. As a result, understanding the fate and transport of radionuclides (e.g., radiocesium [137Cs]) within ecosystems has become a primary interest of radioecological research. However, to date few studies have assessed the role of decomposers and scavengers in the transport of radionuclides within food webs. Our objectives in this study are to quantify bioaccumulation of 137Cs among invertebrate scavengers utilizing contaminated carrion, and elucidate the proportion of total 137Cs activity within carcasses assimilated within invertebrate communities. Using flies as our model species, we are quantifying assimilation of 137Cs from contaminated carrion to various stages of fly development, as well as the overall proportion of 137Cs transferred from carcasses to invertebrate scavengers. The results of this study will provide novel information on the role invertebrate scavengers play in the fate and transfer of 137Cs within food webs in contaminated areas.

EFFICIENCY AND DYNAMICS OF CARRION REMOVAL IN THE SOUTHEASTERN UNITED STATES

SREL Collaborators: Jim Beasley, Miranda Butler-Valverde, Travis DeVault, Olin Rhodes, Jr.

Scavenging is a pervasive foraging strategy among vertebrates, yet researchers have only recently begun to recognize the importance of understanding scavenging relationships in food web dynamics. The fate and composition of communities using carcass resources is influenced by a myriad of abiotic (e.g., weather) and carcass (e.g., species, size) attributes. However, scavenging studies have predominantly only assessed scavenger use of lower trophic level (i.e., herbivore) carrion. This research aims to broaden our understanding of scavenger dynamics, and the mechanisms driving potential differences in scavenging rates of carrion of varying trophic levels. We are conducting a series of field studies with higher trophic level carrion (e.g., vultures, coyotes) paired with herbivore carcasses to elucidate underlying differences in the fate of carrion resources among scavenging guilds. Researching higher trophic level carrion scavenging dynamics will increase our understanding of the flow of nutrients in ecosystems, which potentially has financial and environmental implications.