Am Bratach No. 223
In makes you wonder why they would want to leave the warm weather, pristine beaches, dense jungles and great rivers of the southern hemisphere. In actual fact they are not ours and Africa is not their winter vacation. They are just visitors here and their home is really Africa.
Bird migration is primarily a Northern Hemisphere phenomenon. There are 600 species in Europe and only 40% stay in the area for the summer. Why is that? I guess it all started after the last ice age. 15,000 years ago the whole of Northern Europe would have been covered in ice. 11,000 years ago the ice started to melt and the ice cap retreated.
Over the next few thousand years, different types of vegetation spread slowly northwards. New habitats were created and many birds moved north following their habitats. Some birds however, such as the swallow, had been perfectly happy in the southern areas and could doubtless have gone on living there all year. Since they could not survive the winter in the north why should they bother to go there? One reason was that they were living in close association with many other birds, and competition was intense. As the ice retreated to the north, new areas became available to them, areas that were, to start with, empty of birds. A swallow that migrated northward to these areas found plenty of food, little competition and longer days in which to hunt. The birds able to migrate were able to raise more young and natural selection favored the migrant. As the ice retreated further still, the winter and summer places for the migrant moved progressively further apart. However as long as the migrant continued to raise more young than the bird which stayed at home, it was still at an advantage.
As the two areas moved further apart the birds would have faced another problem: was it worth the effort of returning to the southern area for the winter? Migration is difficult and dangerous and has many risks. Many get blown off course, many get shot or die of starvation en route. Some species like the stonechat decided it was better to stay and brave out the winter (Wow! They must have been regretting that decision this winter), while others continue to make the massive journey to their ancestral home every year.
One of my favourite and most remarkable of all the summer migrants has to be the wheatear. It has a distinctive white rump that it flashes as it disappears into the nearest rabbit burrow in search of a nest site. It loves the closely cropped short grass on the machair at Clachtoll and Stoer. It is also colloquially known as a chick chack, clod hopper or stone chucker because of its characteristic chatting alarm call. This tiny bird (less than 1oz) migrates to Northern Europe and some of them now fly through Siberia, across the Berring Straits into Alaska and North America (a 75,000 miles 1-way trip). Then they fly all the way back again in the autumn. I feel like showing them an atlas of the world and telling them just to fly down to South America for the winter and save their energy. It must have a similar climate to Africa.
So when I see the first swallow appear over the croft this spring to nest in the old byre, I feel honored that it has made this epic journey. I am not sure I would.
Andy is a senior Highland Council countryside ranger, based at Lochinver.