There are many other reasons, too. At night, the winds die down so flying is smoother. The temperatures are cooler so the exercising birds don't overheat. Seeing the stars helps the birds navigate. They can fuel up during the day for their long night flights.
Birds can actually feel changes in air pressure in their inner ear.
When the pressure goes down, birds feed a lot more, as if anticipating a storm. In the body of your message, give your answer to the question above. Copyright 2000 Journey North. All Rights Reserved.