As summer nears end, barn swallows get ready to depart
As summer draws to a close, Barn Swallows are gathering on fences, telephone wires, overhead power transmission lines and other vantage points getting ready to depart. In the past nobody knew where they went; nowadays we are better informed but are still learning about their amazing journeys.
The Barn Swallow is found almost worldwide and while all of the millions of individuals are regarded as belonging to the same species at least five or six distinct sub-species and a number of other 'forms' are recognised.
Only one sub-species has been recorded to date in Ireland. Outside of our shores our sub-species is known to breed at far north as the southern fringe of the Arctic Circle, as far south as North Africa and as far east as central Asia.
As autumn approaches all of the birds head south. Those from Europe are known to winter in the southern half of Africa. Those from central Asia winter in eastern India. The reason the birds migrate is, of course, to capitalise on the supply of insect food that they feed on.
As autumn approaches here and things turn chilly the number of flying insects drops dramatically so insect-eating birds like the Barn Swallow move south to milder climes were food is more abundant.
It might appear to make sense for migrating birds to fatten up in preparation for the long journey south but it doesn't because the birds must be slim and trim to undertake the marathon event.
Migrating Barn Swallows mainly fly during daylight hours and stay at a low altitude. They cover about 300km per day. Feeding as they travel they keep going except when they get held up by bad weather. The trip takes about six weeks to complete.
All going well, our birds cross over to France and travel south through Spain, cross over to North Africa and either set out across the great Sahara desert or skirt around it.
Those not up to the journey die along the way from exhaustion, starvation, being caught by predators or from weather-related causes. It has been estimated that perhaps only one third of those who set out complete the 9,500km marathon journey. Amazingly, some birds go as far south as South Africa.
As the migrants depart, the cheerful twittering and chattering of Barn Swallows, one of the lovely sounds of summer, is a sound that won't be heard again until the birds arrive back here again next April.