In winter, most of the birds in a forest will fly away to warmer places. This is called migration. Birds migrate for two reasons. The first is that with the approach of winter, food becomes scarce in the forest. So, birds fly to places where food is still plentiful. Moreover, many species cannot tolerate extreme cold, and so they migrate to escape from freezing temperatures.
How do birds know when to migrate? it seems to be an instinct that is triggered by the angle of the sun in the sky, and the amount of day light.
Migrating birds can cover thousands of miles in their annual travels, often traveling the same course, year after year. They may migrate unescorted to a winter home they have never before seen, and return the following spring to the area in which they were born. How do they do this? Birds appear to navigate using a variety of techniques, including navigation by the stars, sensing changes in the Earth's magnetic field, and even by smell. Migration is truly one of the miracles of nature!