Bird Migration

Why did birds start migrating to the UK?  To understand why birds first chose to visit here, we need to go back 10,000 years to the end of the last Ice Age.  New land that had been buried under ice for thousands of years began to appear as the ice melted away, as the climate became milder and wetter.  This made a good place for the invertebrates that many birds feed on to live.  The number of bugs increased over time and birds on the search for food decided that this new land was a good place to find it.  Also, there were fewer predators and not much competition for food as few species had yet arrived on the new land.  This was therefore an ideal home and a great place to lay eggs and raise their young!

So all was well during the summer months.  However, in the winter the invertebrates died in the cold temperatures and it was too cold for many of these newly arrived birds to survive so they flew back to the warmer countries that they had originally come from.  The ones that fled survived better than any that stayed, so they ended up making the journey every year and still do today.

But why leave their southern countries?  Food doesn’t run out there so why fly all the way over here?  It’s because Britain has fewer predators, more space, less competition from other species and longer days in the summer, which means more time in the day to find food.  All these are important to birds when they are trying to raise babies and find enough food for them.

So migratory birds fly backwards and forwards each season between the best place for feeding and the best place for breeding as the seasons change.

How do birds know when to start their journeys?  Well it depends on the type of migration, but generally speaking in Britain there are seasonal clues such as the weather getting colder and the days getting shorter towards autumn time which tells the birds when to leave.However, at the Equator, where there are no seasons and the temperature is fairly consistent throughout the year, it could be the number of days that the birds have been there that makes them restless at about the right time.  For other types of migration, food perhaps becomes harder to find, overcrowding begins to become a problem, or the birds’ fat reserves run low (they get thin and hungry) and they know it is time to move to a new area to find food.

One of the amazing things about bird migration is how the birds know where they’re going.  They can’t read maps or use compasses and it’s a very, very long way, so how on earth do they navigate?   One of the main ways they do it is by learning the route from their ancestors; it is instinctive: it is in their genes that they just know where  to go.  Some bird species have a mineral called magnetite above their nostrils.  This helps them to use the Earth’s magnetic field to navigate.

Scientists also believe that birds use a combination of the landscape features – such as a coastline or mountains, almost like they are reading a map! Finally, some birds, such as starlings, use the position of the sun to guide them and others, such as mallards navigate by the stars.

 

Read More: How do birds survive such long journeys?