From pup to predator; generalized hidden Markov models reveal rapid development of movement strategies in a naïve long‐lived vertebrate

Rapid development of a successful foraging strategy is critical for
juvenile survival, especially for naïve animals that receive no parental
guidance. However, this process is poorly understood for many species.
Although observation of early-life movements is increasingly possible with
miniaturisation of animalborne telemetry devices, analytical limitations
remain. Here, we tracked 29 recently-weaned, grey seal Halichoerus grypus
pups from colonies in two geographically distinct regions of the United
Kingdom. We analysed at-sea movements of pups throughout their initial
months of nutritional independence to investigate the ontogeny of
behaviour-specific (foraging and travelling) movement patterns. Using
generalized hidden Markov models (HMMs), we extended the conventional HMM
framework to account for temporal changes in putative foraging and
travelling movement characteristics, and investigate the effects of
intrinsic (sex) and extrinsic (environment) factors on this process.
Putative foraging behaviour became more tortuous with time, and travelling
became faster and more directed, suggesting a reduction in search scale
and an increase in travel efficiency as pups shifted from exploration to
an adult-like repeatable foraging strategy. Sex differences in movement
characteristics were evident from colony departure, but sex-specific
activity budgets were only detected in one region. We show that
sex-specific behavioural strategies emerge before sexual size dimorphism
in grey seals, and suggest that this phenomenon may occur in other
long-lived species. Our results also indicate that environmental variation
may affect the emergence of sex-specific foraging behaviour, highlighting
the need to consider interacting intrinsic and extrinsic factors in
shaping movement strategies of long-lived vertebrates. Moreover, comparing
the behavioural state estimations to those of a conventional HMM (no
variation in statespecific movement parameters) revealed differences in
the amount and location of foraging activity, with implications for
spatial conservation management. Overlooking intrinsic and extrinsic
variation in movement processes could distort our understanding of
foraging ecology, population dynamics, and conservation requirements.