We are still at the farm in Northumberland where we are having a lovely Indian summer, with morning mist in the valleys burning off to reveal bright sunlit landscapes. We have been working with the falcons, flying them every day at robotic prey birds and learning more and more about their development and flying skills high in the sky.
The last broods of house martins fledged from the eaves on the south side of the house, and the swallows from the sheds and stables two weeks ago. The stubby tailed youngsters flitted around the steading for a few days while they grew their long feathers, developed their muscles and perfected their hunting skills. Now they are forming little groups, clustered on the wires, psyching themselves up to move south.
Each swallow weighs just a few grams, a tiny little bundle of feathers. Having designed robotic birds I am only too aware that in a flying bird every part of a gram has to be justified. A swallow carries no surplus, nothing at all. You could hand one over to the most eminent committee of scientists and they could not get rid of half a gram from the design of a swallow. Even the meagre fat stores are distributed to balance the centre of gravity and provide for the journey ahead. Just as in designing we use trial and error and lots of iterations to develop our robotic birds, swallows are the results of billions of iterations, tested over millions of years by evolutionary pressures.
Inside the brain of this tiny bird are a few molecules stored away. They are very special. They are responsible for philopatry, the urge to return to the place of our birth. We all have such a response and express it in different ways. I find it incredible that inside that little swallow, winging its way all south through Europe to Africa, not only does it finds its way to its traditional wintering areas, but, when the time comes in spring, those few molecules will lead it all the way home, right back to the exact beam in the stable where it was hatched. I will come into the house and call ‘Mrs Fox! Spring is here! Our friends are back from Africa!’
Seeing them go brings mixed feelings, like seeing children off to their first days at school. I think that it is our duty to provide these youngsters as part of our contribution to the future of the living world. It is not an onerous responsibility. Sometimes they make a mess in the porch or window ledge, but a strategically place old piece of slate will hold the droppings until the nest is finished. All children make a bit of mess. And when they are gone, the empty nests bring back memories of those little yellow lined mouths peeking out, and of long summer days. Maybe the nests will fall in the winter storms. But somewhere out there on the African savannas, there are a few little molecules of memory that will lead our swallows home again to renew their ancient cycle.