Unifying adaptive stress and adaptive habitat selection hypotheses through movement ecology

1. Glucocorticoid production is often indicative of internal state that underpins movement and resulting habitat selection. Habitat selection is adaptive behaviour, but habitats where animals exhibit atypical glucocorticoid production are often associated with low fitness. Discrepancies between poor fitness outcomes and purported adaptive behaviour have contributed to a lack of consensus about the ecological and evolutionary implications of glucocorticoid production. 2. We aim to demonstrate the adaptive ecological and evolutionary roles of glucocorticoids by integrating stress physiology with habitat selection theory. 3. First, we show how habitat selection theory can benefit from a mechanistic understanding of the relationships between stressors, internal state, and habitat selection. We show that glucocorticoids drive everything from short-term locomotion to large-scale movements. In turn, these movements produce familiar patterns of adaptive habitat selection like habitat specialization and migration. Populations arrive at these evolutionarily stable habitat selection strategies by responding to stressors like predation and food availability. To quantify responses to stressors, we show how to parameterize glucocorticoid data in habitat selection models. Modelling the ecological and evolutionary patterns that make habitat selection adaptive also help clarify relationships between glucocorticoids, stress, and fitness. 4. Our approach delivers a practical framework for testing existing hypotheses about habitat selection and stress physiology. Our framework can also be applied to new questions that integrate both, with the potential to understand adaptations of populations to their environments, and implications of stressors and habitat selection for ecosystem functioning. ### Competing Interest Statement The authors have declared no competing interest.