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Migrating birds

Swallows. Photo Margaret HollandSwallows. Photo Margaret Holland

By Sarah J. Dodd

A sure sign of approaching autumn is the September spectacle of swallows gathering on telephone wires, preparing to migrate to Africa for the winter.

They are not the only species that will travel to a warmer climate to escape our cold Cumbrian weather; many others follow suit, including the ospreys at Bassenthwaite. But where exactly do they go? And how do they find the way?

Volunteers at Bassenthwaite are hoping to answer the first question by tagging ospreys and monitoring their progress with satellite trackers. The breeding pair return each year from their 3000-mile trip to Africa, somehow managing to find their way back to exactly the same nesting site across the lake from Dodd Wood.

The brain mechanism that guides the birds is still a mystery, but scientists have a number of theories: Juvenile birds learn the way to go by simply following their parents the first time they migrate, but there are many cases where birds fly on their own and still follow the same route. Scientists believe that they may be able to sense the Earth’s magnetic field and use it to navigate. They may also take into account the position of the sun and stars to help them stay on the flight path.

So how do the ospreys and those September swallows know that it’s time to depart? Birds are highly sensitive to changes in day length. The reduced hours of daylight at this time of year trigger the release of hormones that make the birds restless to leave, and also help the birds lay down fat reserves in preparation for their long journey.

Yet, later in the autumn, many wading birds and geese will arrive in places such as Morecambe or the Solway Firth to over-winter here. As always, nature ensures that the balance of birdlife in Cumbria is restored. A great place to see migratory birds is South Walney Nature Reserve.  

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