Tracking red deer population size using deterministic cohort analysis

Reliable and cost-effective monitoring tools to track population size over time are of key importance for wildlife management and conservation. Deterministic cohort analysis may be used to this aim, especially in hunted populations, but it requires that all mortality events are recorded and that individual age at death is known exactly. In this study, we investigated the reliability of cohort analysis as a relative index to track over-time variation in red deer (Cervus elaphus) abundance, in the absence of exact information about natural mortality and age. Visual tooth inspection was used to age 18,390 individuals found dead or hunted between 1982 and 2020 within the Trentino sector of the Stelvio National Park and the Val di Sole hunting district (Central Italian Alps). Temporal trend of reconstructed population size was checked using spring spotlight counts as a benchmark, through the Buishand range test and a linear model. Our results showed a significant and positive relationship between reconstructed population size and spring spotlight counts between 1982 and 2013, suggesting that cohort analysis could reliably track red deer population trend up to 7 years in the past. With a relative error of  +  1.1 (SD  =  1.5) years in the estimation of age, and fairly stable hunting pressure, our results support the use of deterministic cohort analysis as a relative index of abundance for monitoring red deer over time, even in the absence of exact information about natural mortality. Under violation of assumptions, however, the performance of deterministic reconstruction should be carefully inspected at the management scale.