Behavioral transition probabilities in dugongs change with habitat and predator presence

Background/Question/Methods

Although not widely appreciated, prey can manage predation risk by modifying the sequence of their behavioral states.  We explored this phenomenon in dugongs (Dugong dugon) subject to spatially and temporally variable risk of tiger shark (Galeocerdo cuvier) predation in Shark Bay, Australia.  Dugong behavior was assayed using focal follows and organized into sequences of foraging, resting, and traveling bouts.  We used log-linear analysis to test for sequence differences in relation to habitat (deep, shallow) and predation danger (sharks present, largely absent).  

Results/Conclusions

Dugongs modified their behavioral sequences between periods of high and low shark abundance: those at risk alternated more frequently between foraging, which constrains anti-predator vigilance, and traveling, which facilitates predator detection.  Dugongs also avoided continuous series of resting bouts, during which awareness is reduced, when sharks were present.  These changes were only observed in relatively dangerous shallow habitat, which is hunted disproportionately by tiger sharks; behavioral responses to sharks in deep habitat were modest. We conclude that dugongs in risky habitat resort to safer behavioral sequences in response to sharks.  Given that human disturbance and predators are perceived similarly by many species, some forms of vessel interaction could compromise the fitness of sirenians by eliciting similar behavioral adjustment.