Most people are aware that at this time of year, at the moment we’re just coming into May, we are seeing and we’re expecting swifts, swallows and house martins to be coming back from their winter feeding grounds in Africa.
And once they’re here, they start nest building, they’re breeding, and they’ve flown a long long way in order to get here. And then once autumn approaches the weather gets colder and the adults and the young but mature birds they sort of psyche themselves up and suddenly they’re gone. They’re all migrating southwards again back to Africa.
Observations of birds that have been ringed, they looked at 23 species of migrating birds and found that over the years the timing of the migrations has become earlier by sort of two to twelve days. That major migration route, it sort of starts in the high Arctic and it then passes through Scandinavia.
Heligoland is actually on a major bird motorway, if you like. It consists of two islands, one of them is called Heligoland, and that one is very small, it’s just one kilometre squared. The other one is even smaller and it’s called Dune. As the birds fly of course they’re using up all of their energy.
So Heligoland is a very important stopover point for the birds to replenish their food supplies. Now you can tell how utterly important it is for birds to have enough energy to fly, simply because they’re flying such huge distances.
So before the birds actually set off to migrate they start eating more. There’s some research being done which has shown that smallish birds that are getting ready to migrate they will eat up to 1.5 gram of fat a day for 10 days before they actually set off, and by the time they’ve set off up to 40% of their body weight could be fat. But clearly there’s a limit to how much they can carry because it’s going to start impacting on their ability to fly.
Now it’s been estimated that a little bird can fly about 2.500 kilometres on its body fuel supplies. But of course the bird could meet bad weather. So somehow they have to factor in an allowance for that. So the distance they fly without a stopover isn’t necessarily as long as 2,500 kilometres. And of course that distance varies according to species anyway.
So stopovers are of crucial importance to birds. Now given the position of Heligoland right there on that major migratory route this is where they’re going to stop to take on board more food. In the autumn when they are flying southwards from their summer breeding grounds they can land on Heligoland and rest and they can stock up. They can stock up with food, and then they’ll be back on their way again.