The foraging behaviour and body condition of northern bottlenose whales (Hyperoodon ampullatus)

Despite foraging being critical for survival, characterising foraging behaviour in marine animals is inherently challenging. Found in deep offshore habitats, beaked whales are the least known cetacean family, whose foraging behaviour (besides echolocation) remains poorly understood. This thesis provides insights into the foraging behaviour of northern bottlenose whales, a data-deficient species of beaked whale with an uncertain conservation status. Fine-scale sound- and movement-recording tags were deployed on the little-known north-eastern Atlantic population. Using echolocation buzzes as a proxy for prey-capture attempts, Chapter Two characterises prey-capture kinematics. Buzz-associated movements consisted of dynamic translational and rotational motions, and complex rolling manoeuvres. Building on this knowledge, Chapter Three develops a method of detecting prey-capture attempts using accelerometer data. Concordance with rolling behaviour demonstrated that rapid changes in acceleration (jerk) successfully predicted foraging buzzes, paving the way for detecting foraging behaviour over longer time-scales. The starvation-predation trade-off and condition-dependent risk-taking concepts are cornerstones of foraging theory, but little explored in marine top predators. Chapter Four shows that the whales exchanged foraging effort for predator-avoidance behaviour; however, contrary to theoretical predictions, individuals in poorer body condition foraged less and had higher levels of predator-avoidance behaviour, which suggests that body condition was a consequence rather than driver of behaviour for the animals sampled in this study. Chapter Five reveals that northern bottlenose whales at two sites (the Gully and Jan Mayen in the western and eastern North Atlantic respectively) varied substantially in foraging depths and time budgets, possibly reflecting differences in prey availability and interspecific competition. Although this thesis provides an understanding of the foraging behaviour and ecology of a little-known whale species, the methods developed (e.g. for determining prey-capture kinematics) and the knowledge revealed (e.g. how body condition relates to behavioural trade-offs) are applicable and relevant to both marine and terrestrial animals.