5. Birds carry a kind of internal clock that prepares their bodies for travel
Almost like athletes, birds begin physically preparing for migration well in advance of the journey. They start to eat more and gain weight, their liver and reproductive organs often shrink, and their cell membranes change to enable oxygen and fat to be used more efficiently. Some birds renew their flight feathers, which can take up to a month.
6. Migrating birds can be divided into “calendar birds” and “weather birds”
We don’t know exactly what makes birds migrate when they do. Some birds set out at exactly the same time each year, whereas the departure times of others are based on the weather.
In Borneo, the annual arrival of the brown shrike is so consistent that farmers used to rely on it to know when to plant their crops.
7. The migration route of many birds is etched into their genes
Although a lot of large birds – such as swans and geese – follow more experienced relatives, many smaller birds make their first migration without a guide. It’s thought they inherit a kind of internal com that tells them where to go.
When scientists crossbred birds with different migratory routes, the offspring followed a path halfway between those of their parents.
8. Birds can return to a specific place year-on-year – even to the same twig!
First-time migrants will only have a rough idea of when they’ve arrived in the right area, based on temperature, light and food availability. But on subsequent journeys they return to the exact same place. Scientists still don’t fully understand how this precise navigational memory works.
