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Contributed Talk

Session: : Behavior: Migration And Movement 3

COS 184-2 - A parametric model for estimating the timing and intensity of animal migration

Wednesday, August 9, 2023
1:45 PM – 2:00 PM PDT
Location: B112
Abstract: Animals of many different species, trophic levels, and life history strategies migrate, and the improvement of animal tracking technology allows ecologists to collect increasing amounts of detailed data on these movements. Understanding when animals migrate is important for managing their populations, but is still difficult despite modelling advancements. We designed a model that parametrically estimates the timing of migration as signaled by changes in both step length and turning angle distributions. Specifically, the model relies on the hypothesis that animals move with higher speed and directional persistence during their migration. We use maximum likelihood techniques to estimate exactly how an animal’s movement behavior changes between migratory and non-migratory states, supplementing these parameter estimates with confidence intervals generated via parametric bootstrapping. The model estimated the temporal extent of migratory behavior more accurately and precisely than competing methods when applied to simulated data. We also tested our model on three datasets: migratory ferruginous hawks (Buteo regalis) in the Great Plains and barren-ground caribou (Rangifer tarandus groenlandicus) in northern Canada, and brown bears (Ursus arctos) from the Canadian Arctic. We estimated the beginning and end of migration in caribou and hawks to the nearest day, while confirming a lack of migratory behavior in the brown bear population. In addition to estimating when caribou and ferruginous hawks migrated, our model also identified differences in how the two populations migrated; ferruginous hawks achieved efficient migrations by increasing their movement rates while caribou migration was achieved through significant increases in directional persistence. We anticipate that rigorous assessment of migration metrics will aid understanding of both how and why animals move.