With our sustained cooler than average temperatures, many birds are making their yearly trek south for the winter months.
The cold air causes a change in food supply, causing birds to move to an area where they can find something to eat. Birds stopped in a sunflower field to fill up during their trip south. Some birds almost double their body weight by storing fat before migration.
Many birds also eat insects, so as the insects die off with the cold air, birds fly to warmer climates to find food. Some birds only fly a short distance, just far enough to find the necessary food.
It's interesting to know that not all birds fly south for the winter. If you have a bird feeder, leave it out this winter supplied with food and see for yourself.