They want a tail wind-for the south wind to come along and help them move north. So, knowing when to migrate involves an internal clock, a feel for temperature, and the right weather patterns that create south winds. What you see looks very similar to velcro. How does velcro work. Birds take great care of their feathers-they have to, because if they didn't, they would get cold and wet and would not be able to fly.
Many birds have an oil gland at the base of the tail.
The bird rubs its beak on the gland to get oil on it. Then it rubs the oil off its beak onto its feathers. This is called preening. The oil makes the feathers water-resistant. Birds also straighten their feathers by running each feather through the beak to make the velcro-like structures zip together to keep the feather intact.