How do animals know when to migrate?

Animals know when to migrate through a combination of innate biological mechanisms and environmental cues, blending hard-wired instincts with learned behaviors to varying degrees depending on the species. Many migratory species possess internal biological clocks, often linked to changes in daylight length (photoperiod), temperature, and hormonal shifts, which trigger the urge to migrate. For example, birds have an internal circannual rhythm that helps them anticipate seasonal changes, prompting migration at specific times of the year even without prior experience. This innate timing is considered a hard-wired instinct, ensuring that animals begin migration when environmental conditions are favorable for survival and reproduction. At the same time, some aspects of migration are learned or refined through experience. Young animals may follow adults or flock members on their first migration, learning routes, stopover sites, and feeding grounds. In species like whooping cranes, captive-bred individuals have been taught migration routes using ultralight aircraft, highlighting the role of learning when natural guidance is unavailable. In social animals, cultural transmission of migratory knowledge can also occur, blending instinct with learned behavior. In summary, migration timing is primarily driven by hard-wired biological rhythms and environmental cues, but learning and experience play important roles in navigating routes and adapting to changing conditions. This combination helps ensure the success of migratory journeys across diverse animal species.