You can be forgiven for never having come across this word before – it cropped up in a book I’ve just finished reading about how different animals perceive the world (‘An Immense World’ by Ed Yong – well worth a read). Zugunruhe is a German word that means ‘migratory restlessness’. It’s a thing that happens to birds as they start getting anxious when the time for them to start their migration draws near. The symptoms include fluttering wings, sleeplessness and general disruption to the birds’ normal activities. Birds in captivity are affected by it as well – caged birds will launch themselve at the walls in the direction they want to travel in. Sad, right?
As I said, this is a German word, which is made up of ‘Zug’ meaning ‘move’ or ‘migration’, and ‘unruhe’ for ‘anxiety’ or ‘restlessness’. It first appeared in 1707, and is now well recognised in ornithology.
Around one in five of all the world’s bird species migrate. And just before setting off, some have been found to atrophy organs that they don’t need while they’re flying (like their digestive organs), while beefing up those that they need for power (like pectoral muscles and hearts). Amazing.
Here are some more awesome migration facts.
Bar-headed geese travel from their breeding areas in Mongolia, the Tibetan Plateau and northern China to India. They cross over the Himalayas using less than ten per cent of the oxygen available at sea level (I confess I don’t really understand what this means, but I guess it’s impressive…?), and reach altitudes of up to 23,000 ft (7,000 m). That. Is. Well. High.
Great snipes put on a lot of weight before their winter migration. Despite this giving them a lack of aerodynamism, they’ve been recorded reaching speeds of up to 60mph (97kmph) over a distance of 4,225 miles (6,800 km). They don’t take any breaks while flying from Scandinavia to sub-Saharan Africa, and arrive much thinner than they started, losing half of their weight en route.
Bar-tailed godwits (great name for a band) travel from Alaska to New Zealand, and hold the record for the longest non-stop flight of any bird. They fly for over 6,835 miles (11,000 km) without stopping.
It’s not all about flying either. Adélie penguins trek around 8,077 miles (13,000 km) across ice every year.
The Arctic tern has the longest migration known in the animal kingdom. It travels 55,923 miles (90,000 km) every year, going from pole to pole. Arctic terns can live for up to 30 years, which someone much cleverer than me has worked out means that a single tern’s migration distance is the equivalent of going to the moon and back more than three times.
Most of the birds on this list are endangered due to climate change and habitat loss. Have a look at BirdLife International or World Animal Protection if you’d like to find out more about ways to protect them and our other furry friends.