Elephant seals in poorer body condition trade sleep for foraging

Sleep provides physiological benefits, but sleeping animals are unable to gain energy from foraging to fuel migration, self-maintenance, and reproduction¹. Therefore, trade-offs may exist between sleeping and foraging under energetic and ecological constraints^2,3. We use cutting-edge animal-borne sensors (bio-loggers) to show that northern elephant seals (Mirounga angustirostris) in poorer body condition have higher locomotory costs and exhibit less efficient foraging, which requires them to forage more and sleep less. Our results demonstrate that wild elephant seals can adjust their time-activity budgets to break out of a negative feedback loop of reduced fat stores and less efficient foraging, which likely promotes population persistence.