Enhancements to population monitoring of Yellowstone grizzly bears

In the Greater Yellowstone Ecosystem, counts of female grizzly bears (Ursus arctos) with cubs-of-the-year (females cubs) from systematic aerial surveys and opportunistic ground sightings are combined demographic data to derive annual population estimates. We addressed 2 limitations monitoring approach. As part a rule set, conservative distance >30 km currently is used as threshold assign unique females cubs, resulting in underestimation bias. Using telemetry locations cubs collected during 1997–2019, we created 1,000 sets for each 5 levels simulated number by selecting among these locations, evaluated classification performance alternative criteria (12–30 km). Under all scenarios, 12–16-km maximized minimized estimation bias; 16-km criterion was optimal current conditions sampling efforts. Our second objective test generalized additive models (GAMs) flexible trend analysis technique. time series 10 scenarios (10, 15, 20% decline over periods 5, 10, 15 yrs, plus stability), applied GAMs, assessed metrics associated posterior distribution instantaneous rate change. detected declines >99.6% replicates under 84.7–94.7% 10% scenario. From onset first detection, ranged 3.7 (20% yrs) 11.1 (10% yrs), 3.9–8.8 years mean duration detection events. The GAM approach allows directional changes trend, including early warning metrics, stabilization after such changes. Retrospective application GAMs resulted higher estimates growth rates than reported using methods.