This is important because it’s the definitive and acknowledged sign that spring is here.
What will actually happen is that the sandmartins will arrive first. They have a shorter migration. They over-winter in central Africa, while almost all Irish swallows have to fly from Natal Province in South Africa. We don’t have housemartins around here so I’m not sure when they arrive. The sandmartins have a nesting colony in a disused quarry about 800m away.
The male swallows will arrive first, 10 days or so before the females. They have two immediate priorities. One is to capture enough insect food to build up their body weight after the long migration — although they already had a feeding spree in Spain and south-western France after the Mediterranean crossing. The other priority is to secure the nest site.
Almost all Irish swallows nest in buildings or other man-made structures, such as bridges or wharves. They are very faithful to their nesting sites, returning to the same one generation after generation over decades or even centuries. If something happens to the nest site over the winter — if a building is demolished or if the access is blocked up — they get extremely agitated. I’ve known them to actually lose their lives in frantic attempts to get into a sealed building.
But if all goes well they’ll reoccupy the old site and wait for the females. Swallows are reasonably monogamous but the hazardous migration leads to many casualties, meaninga number of widows and widowers in need of new partners. Two things make a male swallow attractive to an unattached female. One is the possession of a good nest site and the other is the length of his tail streamers.
When all that’s sorted out they need a nest. Sometimes they repair an old one but more often they start a new one beside it. Construction is of small mud bricks mixed with sticky saliva. Some plant fibres or grass stems are used as reinforcement and feathers are also incorporated, particularly in the lining. The mud is collected by the beakful by landing by a puddle or on the bank of a pond or stream.
A normal clutch size is four to five eggs and the female does most of the incubating, though both parents share the task of feeding the young. In Ireland, two broods a year are normal, though they may manage a third in an ideal summer. This large number of offspring is needed to compensate for the losses incurred during the long migration. Despite this, swallows, which have a wide global distribution, breeding in Europe, Asia, and North America, have declined in numbers in recent decades.