An evaluation of behavior inferences from Bayesian state‐space models: A case study with the Pacific walrus

Abstract

State‐space models offer researchers an objective approach to modeling complex animal location data sets, and state‐space model behavior classifications are often assumed to have a link to animal behavior. In this study, we evaluated the behavioral classification accuracy of a Bayesian state‐space model in Pacific walruses using Argos satellite tags with sensors to detect animal behavior in real time. We fit a two‐state discrete‐time continuous‐space Bayesian state‐space model to data from 306 Pacific walruses tagged in the Chukchi Sea. We matched predicted locations and behaviors from the state‐space model (resident, transient behavior) to true animal behavior (foraging, swimming, hauled out) and evaluated classification accuracy with kappa statistics (κ) and root mean square error (RMSE). In addition, we compared biased random bridge utilization distributions generated with resident behavior locations to true foraging behavior locations to evaluate differences in space use patterns. Results indicated that the two‐state model fairly classified true animal behavior (0.06 ≤ κ ≤ 0.26, 0.49 ≤ RMSE ≤ 0.59). Kernel overlap metrics indicated utilization distributions generated with resident behavior locations were generally smaller than utilization distributions generated with true foraging behavior locations. Consequently, we encourage researchers to carefully examine parameters and priors associated with behaviors in state‐space models, and reconcile these parameters with the study species and its expected behaviors.

Putting the behavior into animal movement modeling: Improved activity budgets from use of ancillary tag information

“…Information about vertical movements is one of the most common ancillary data types collected in studies of aquatic movement ecology (Hussey et al., ). Furthermore, the SMRU‐SRDL tags documenting haulout, diving, and other behavioral summaries (Photopoulou, Fedak, Matthiopoulos, McConnell, & Lovell, ) are being ever more widely deployed across species including seals (Hindell et al., ), narwhals (Lydersen, Martin, Gjertz, & Kovacs, ), salmon sharks (Block et al., ), turtles (Benson et al., ), sea lions (Lowther, Harcourt, Page, & Goldsworthy, ), and walruses (Beatty et al., ). The approach presented here may be easily up‐taken and fit by ecological users across a range of appropriate data sets.…”

“…Achieving greater biological realism in animal movement models is essential for making correct inferences about space use and behavior, and developing activity or energy budgets. For example, movement models frequently applied to marine mammals (Jonsen, Flemming, & Myers, ; Morales et al., ) may oversimplify complex behaviors (Beatty, Jay, & Fischbach, ; Ramasco, Barraquand, Biuw, McConnell, & Nilssen, ). Time spent in activities other than transit or forage can be important, for example, resting, predator evasion, or social behavior, so an increased harnessing of activity information may yield greater biological realism in movement process models.…”