  In this paper, we propose a general hidden state random walk model to
describe the movement of an animal that takes into account movement taxis with
respect to features of the environment. A circular-linear process models the
direction and distance between two consecutive localizations of the animal. A
hidden process structure accounts for the animal's change in movement behavior.
The originality of the proposed approach is that several environmental targets
can be included in the directional model. An EM algorithm is devised to fit
this model and an application to the analysis of the movement of caribou in
Canada's boreal forest is presented
