title: Hidden Markov models reveal complexity in the diving behaviour of short-finned pilot whales.
abstract: Diving behaviour of short-finned pilot whales is often described by two states; deep foraging and shallow, non-foraging dives. However, this simple classification system ignores much of the variation that occurs during subsurface periods. We used multi-state hidden Markov models (HMM) to characterize states of diving behaviour and the transitions between states in short-finned pilot whales. We used three parameters (number of buzzes, maximum dive depth and duration) measured in 259 dives by digital acoustic recording tags (DTAGs) deployed on 20 individual whales off Cape Hatteras, North Carolina, USA. The HMM identified a four-state model as the best descriptor of diving behaviour. The state-dependent distributions for the diving parameters showed variation between states, indicative of different diving behaviours. Transition probabilities were considerably higher for state persistence than state switching, indicating that dive types occurred in bouts. Our results indicate that subsurface behaviour in short-finned pilot whales is more complex than a simple dichotomy of deep and shallow diving states, and labelling all subsurface behaviour as deep dives or shallow dives discounts a significant amount of important variation. We discuss potential drivers of these patterns, including variation in foraging success, prey availability and selection, bathymetry, physiological constraints and socially mediated behaviour.
authors.affiliation: Division of Marine Science and Conservation, Nicholas School of the Environment, Duke University, Beaufort, North Carolina 28516, USA.
authors.forename: Nicola J
authors.initials: NJ
authors.lastname: Quick
authors.affiliation: School of Biology, University of St Andrews, Bute Building, St Andrews, Fife KY16 9TS UK.
authors.forename: Saana
authors.initials: S
authors.lastname: Isojunno
authors.affiliation: Zoology School of Biological Sciences, University of Aberdeen, Tillydrone Ave, Aberdeen, AB24 2TZ, UK.
authors.forename: Dina
authors.initials: D
authors.lastname: Sadykova
authors.affiliation: Division of Marine Science and Conservation, Nicholas School of the Environment, Duke University, Beaufort, North Carolina 28516, USA.
authors.forename: Matthew
authors.initials: M
authors.lastname: Bowers
authors.affiliation: Division of Marine Science and Conservation, Nicholas School of the Environment, Duke University, Beaufort, North Carolina 28516, USA.|Electrical and Computer Engineering, Pratt School of Engineering, Duke University, Durham, NC 27708, USA.
authors.forename: Douglas P
authors.initials: DP
authors.lastname: Nowacek
authors.affiliation: Division of Marine Science and Conservation, Nicholas School of the Environment, Duke University, Beaufort, North Carolina 28516, USA.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Read
mesh_terms: D000818:Animals; D001522:Behavior, Animal; D004242:Diving; D005260:Female; D008297:Male; D008390:Markov Chains; D050686:Whales, Pilot