Standardizing protocols for determining the cause of mortality in wildlife studies

Mortality site investigations of telemetered wildlife are important for
cause-specific survival analyses and understanding underlying causes of
observed population dynamics. Yet eroding ecoliteracy and a lack of
quality control in data collection can lead researchers to make incorrect
conclusions, which may negatively impact management decisions for wildlife
populations. We reviewed a random sample of 50 peer-reviewed studies
published between 2000 and 2019 on survival and cause-specific mortality
of ungulates monitored with telemetry devices. This concise review
revealed extensive variation in reporting of field procedures, with many
studies omitting critical information for cause of mortality inference.
Field protocols used to investigate mortality sites and ascertain the
cause of mortality are often minimally described and frequently fail to
address how investigators dealt with uncertainty. We outline a
step-by-step procedure for mortality site investigations of telemetered
ungulates, including evidence that should be documented in the field.
Specifically, we highlight data that can be useful to differentiate
predation from scavenging and more conclusively identify the predator
species that killed the ungulate. We also outline how uncertainty in
identifying the cause of mortality could be acknowledged and reported. We
demonstrate the importance of rigorous protocols and prompt site
investigations using data from our 5-year study on survival and
cause-specific mortality of telemetered mule deer (Odocoileus hemionus) in
northern California. Over the course of our study, we visited mortality
sites of neonates (n = 91) and adults (n = 23) to ascertain the cause of
mortality. Rapid site visitations significantly improved the successful
identification of the cause of mortality and confidence levels for
neonates. We discuss the need for rigorous and standardized protocols that
include measures of confidence for mortality site investigations. We
invite reviewers and journal editors to encourage authors to provide
supportive information associated with the identification of causes of
mortality, including uncertainty.