Directional data in time series

I have data on the heading kept by an animal during a migratory movement.
I would like to represet this data not using a circular plot but on a
xy-plot, to represent the change of kept directions over time.

Giulia,

   Without knowing what question(s) your data are designed to answer I'll
offer my opionon: map the migration. See Figure 2.3 and discussion in Bivand
et al. "Applied Spatial Data Analysis with R." This might be the most
effective way of communicating the migratory path.

Regards,

Rich