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. |
