Identifying predators from saliva at kill sites with limited remains

Abstract

Kill-site investigations can yield valuable data about elusive predators and predator-prey interactions, provided the predator species can be definitively identified as the one responsible for the predation event. The traditional method of visually analyzing prey remains to identify predators is prone to observer bias and may be particularly challenging when few remains are present or in systems with congeneric predators. Other potential evidence left by predators, such as scat, may be difficult to reliably link to the responsible predator, whereas tracking requires adequate substrate conditions. Swabbing for predator DNA from saliva is an objective yet underutilized alternative that has primarily been applied to larger carcasses. We demonstrate the usefulness of a saliva-swabbing method for smaller prey with minimal surface area, including kill sites with almost no prey remains or even just a radiocollar left behind. This study is also the first to compare saliva-swabbing success by sample type (carcass remains vs. radiocollar). From 2010 to 2014, in the Loomis State Forest and Okanogan National Forest, Washington, USA, we employed forensic techniques to increase certainty about predator species identification at snowshoe hare (Lepus americanus) kill sites for the ultimate purpose of elucidating predator-prey interactions. Predator saliva was sampled from remains and radiocollars with foam buccal swabs, stored in lysis buffer for shelfstable preservation, and tested for mitochondrial DNA using polymerase chain reaction and species-specific primers. This saliva-swabbing protocol yielded definitive and objective predator species identification for a majority (58.5%) of sampled kill sites (n kill sites = 31/53). Not only were minimal remains often able to yield predator DNA, but swabs from radiocollars provided significantly more predator identifications. Saliva swabbing also provided identifications at 65.5% of kill sites lacking identifiable predator sign and contributed significantly more predator identifications throughout the year when compared with snow-tracking methods. Expanding saliva-swabbing methods to smaller prey, radiocollars, and limited remains should allow for more definitive predator identifications at kill sites than have been possible with commonly employed methods, thus augmenting the potential to understand and manage for predators and prey.

Wildlife whodunnit: forensic identification of predators to inform wildlife management and conservation

“…It is reasonable to expect that snow could help preserve DNA while rain could wash it away which may explain the lack of a net effect from precipitation. Peelle et al (2019) found that amplification success of predator DNA from snowshoe hare kills was more successful when samples were collected from hard surfaces, such as the plastic collar box, compared to soft surfaces such as bite wounds. In contrast, we did not detect an effect of the swabbing surface on amplification success.…”

“…We predicted that DNA collected from artificial surfaces (i.e. the collar and ear tags) would have higher rates of success in amplifying predator DNA (Peelle et al 2019), and we expected that samples of predator DNA collected from the carcasses of larger prey (i.e., adult deer versus elk calves and deer fawns) would also be more successful in providing genetic information because the predator may spend more time handling and feeding on large prey, depositing more saliva.…”

“…Traditional field methods are imprecise, leading to unclassified mortality sites, and can contribute to misidentification of predator species (Onorato et al 2006). Errors may result from investigator experience or over confidence, the challenge of distinguishing predator species based on scat and hair samples (Onorato et al 2006, Morin et al 2016), limited evidence available for examination (Peelle et al 2019), interference of scavengers (Bauer et al 2005), and similar carcass handling styles between predator species (Mumma et al 2014, Elbroch and McFarland 2019).…”

Predation research with electronic tagging

“…Technology that can support predation data from telemetry will continue to develop, including such techniques as eDNA to swab recovered tags and more molecular methods for prey biopsies to understand genotypes and phenotypes of prey and how these relate to selection (Miller et al 2014, Peelle et al 2019). The development of more specific genetic markers and utilization of new types of PCR methods such as droplets digital PCR (Allan et al 2021) methods will enable scientists to generate increasingly accurate links between prey and predators from non‐invasive material such as saliva (Peelle et al 2019).…”

“…Technology that can support predation data from telemetry will continue to develop, including such techniques as eDNA to swab recovered tags and more molecular methods for prey biopsies to understand genotypes and phenotypes of prey and how these relate to selection (Miller et al 2014, Peelle et al 2019). The development of more specific genetic markers and utilization of new types of PCR methods such as droplets digital PCR (Allan et al 2021) methods will enable scientists to generate increasingly accurate links between prey and predators from non‐invasive material such as saliva (Peelle et al 2019). In parallel, identification of genetic markers that allow analysts to identify physiological state based on small biopsies will allow analysts to couple predation events with physiological state, facilitating insights into how compensatory or additive mortality operates within populations of prey as tagged animals are progressively determined to succumb to predation.…”