Willow warbler perched in a bare larch tree, Co. Durham

The incredible journey

The willow warbler is one of our smallest birds. Yet this delicate little creature performs an amazing feat of strength and endurance.

The journey of a willow warbler

The willow warbler may weigh no more than a box of matches and fit snugly into the palm of your hand, but it has a huge journey.

Each year it flies all the way to the UK from Africa, travelling more than 8,000 kilometres (5,000 miles) across seas, mountains and desert to arrive in time for spring. As if that’s not enough, in autumn it flies all the way back again.

The willow warbler is not alone in making this incredible journey. Many different birds, from swallows to ospreys, fly to the UK from Africa each year. 

Many others visit us in winter from colder northern regions, or briefly stop off here as they pass through. All over the world, every year, millions of birds are on the move. This movement is called migration. It is one of the greatest wonders of the animal world.

In the beginning

We have to look back to prehistoric times to understand how migration started. 

About one million years ago, during the last ice age, Europe was much cooler than today. Ice sheets covered much of the north and east - making life too tough for most animals. The majority of bird species lived in southern Europe and Africa, where it was warmer and there was more food.

As the ice age came to an end, the ice sheets began to shrink northwards towards the Arctic. They left behind them a brand new landscape, where the short, wet summer with its long hours of daylight was perfect for insects. 

If you’ve ever battled midges in Scotland, you’ll know just what this must have been like! But billions of bugs make a delicious feast for birds, which started to explore this ‘empty’ new habitat in the north. 

As well as plenty of food, they found good places to breed, few predators and not much competition from other birds. But in winter the weather got cold again and the food ran out, so some birds headed back south. The ones that left fared better than the ones that stayed put. Soon some started to make the journey regularly. 

As the ice sheets shrank further, the northern lands started to fill up with birds. Some species had to travel even further north to find a place of their own. 

But however far they went, they still had to return every year to their old wintering quarters in the south. Over time, these journeys developed into the long-distance migration routes that we know today.

Common or Eurasian crane Grus grus, group on their autumn migration south to Spain

Moving to survive

You may think a willow warbler is crazy to risk its life every year by flying to Africa and back. But life would be even riskier if it stayed put. Believe it or not, migration is all about survival.

All birds need is to find a good place to feed and a good place to breed. But places change with the seasons, and what seemed like a perfect summer home can become a death-trap in winter. 

A willow warbler eats insects. Unfortunately, most insects disappear during our cold winter, whereas in the warm climate of Africa there is an endless supply; enough to keep millions of willow warblers alive and healthy until the next breeding season. 

You might wonder then: if Africa’s so great, why doesn’t the willow warbler stay and breed there? But when it comes to breeding, the UK has some important advantages. 

For a start, we have far fewer birds competing for the same nest sites. Also, our warm, wet summers mean lots of insect food, while our long summer days – when the sun sets much later than it does in Africa – give parents more time to feed their growing chicks. 

And life here is not so dangerous; in Africa, there are many more hungry predators waiting to snap up helpless young birds and their exhausted parents. So migration actually makes survival easier. 

By taking birds from the best places for feeding to the best places for breeding, it helps them to stay alive and to produce young. Of course migration is also a risky business, and many birds fail to complete their journeys. 

But the casualties are often the sick or weak ones. Their genes do not pass to the next generation, so the population as a whole stays fitter and healthier.

Willow warbler perched on a thin branch, Co. Durham