Q. How do migrating birds know where to go?
A. How birds navigate during migration is still a mystery, and different species follow different navigational systems.
Studies suggest birds orientate themselves to the compass points using the position of the sun during the day and the stars at night.
They can
also sense magnetic north. In addition, they use other clues such as lay of the land, smell and sound.
The most extraordinary aspect of bird migration is that the location, route and perhaps even the techniques are wired into their brains. Many migrating birds abandon their young as soon as they fledge, but a short time later, the young make the migration on their own.
Birds that migrate have an innate sense that tells them when it is time to depart and how long the journey may take.
Migrating birds also learn from experience and become familiar with territories - and often end up within metres of the same place after flying thousands of kilometres.
But it is often a perilous journey and many of the stopping-off points along the worlds' "flyways" are under threat. Wetlands in Japan, for instance, have been disappearing at an alarming rate.
Navigation systems also fail and birds end up far from their destination because of weather, exhaustion or human interference. A greater plover from Asia landed on the California coast recently, the first time the bird has been seen in North America.
Many small birds will gain as much as twice their weight to fuel their journey. Whenever possible they glide and use air currents to preserve energy, and some scientists believe the "V" formation of some species makes flying easier.
Some birds are believed to fly non-stop, but others break their journey.
The longest journey of any migrating bird is the Arctic Tern, which travels more than 35,000km from the North Pole to the South Pole and back again each year, roughly the circumference of Earth.
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Further reading
nzherald.co.nz/environment
