How do birds know when to migrate?

Birds know when to migrate through a combination of environmental cues and internal biological clocks. They are able to sense changes in the length of daylight as they approach the end of summer, which triggers hormonal changes in their bodies that prepare them for migration. Additionally, birds can sense changes in temperature, weather patterns, and even the Earth’s magnetic field to help navigate. These cues, along with their instincts, guide them on their long journeys to warmer regions.