Estimating wildlife populations and their dynamics using multiple data sources and a hierarchical integrated model: The case of California's black bears

Abstract

Accurate monitoring of wildlife populations is critical to their effective conservation and management. For populations that are actively harvested, age-at-harvest (AAH) data provide a valuable source of information about their age and sex structure. Bayesian state-space models have been developed to harness this AAH data along with prior knowledge of species' ecology to estimate population sizes, trends and underlying demographic rates. We extended these state-space models further to integrate abundance models using camera trapping data to both inform initial population size and extrapolate to areas without AAH data. Additionally, we formulated a hierarchical integrated model that models the data and populations separately by region while still sharing information across regions to account for socio-ecological differences and inform adaptive local management. We applied our state-space model to estimate the population size and dynamics of black bears within the hunted areas of California over the last decade and used the integrated camera trapping-based model to extrapolate to the non-hunted areas of California to estimate a total statewide average population size over the last 5 years of 59,851 individuals (90% credible interval: 49,412–70,611). We found generally stable population estimates in the hunted regions of the state, though we found evidence of increases in the Cascades region. We estimated high rates of hunting season survival across California compared with those reported in Eastern North America. Future work should incorporate more local data and covariates describing environmental heterogeneity, hunter effort and human–bear conflict to explicitly investigate drivers of black bear population dynamics over broad regions. Practical implication: Our integrated state-space represents an advancement in the estimation of wildlife population size and dynamics across broad areas that can be applied to the monitoring and conservation of any population for which AAH and auxiliary data exist.