  The behaviour of colony-based marine predators is the focus of much research
globally. Large telemetry and tracking data sets have been collected for this
group of animals, and are accompanied by many theoretical studies of optimal
foraging strategies. However, relatively few studies have detailed statistical
methods for inferring behaviours in central place foraging trips. In this paper
we describe an approach based on hidden Markov models, which splits foraging
trips into segments labelled as "outbound", "search", "forage", and "inbound".
By structuring the hidden Markov model transition matrix appropriately, the
model naturally handles the sequence of behaviours within a foraging trip.
Additionally, by structuring the model in this way, we are able to develop
realistic simulations from the fitted model. We demonstrate our approach on
data from southern elephant seals (Mirounga leonina) tagged on Kerguelen Island
in the Southern Ocean. We discuss the differences between our 4-state model and
the widely used 2-state model, and the advantages and disadvantages of
employing a more complex model.
