Brooding Barn Swallows get off to an early start
BARN Swallows normally nest indoors. Long before our species evolved and before barns, sheds, stables and outbuilding became available to them, it is presumed that these birds probably nested in caves and in crevices on cliffs.
Many people welcome swallows nesting in their sheds as it is believed that the presence of the birds brings good luck. The birds are not so welcome in tidy workshops and in garages where cars parked under a nest are subjected to daily splattering by the busy parents at work overhead.
Some people will tell you that the same pair of Barn Swallows have been using the same nest year in year out for a long period of time. On the face of it, the claim appears to be unlikely. How can one tell the difference between one pair of swallows and another? And, how could a swallow find the exact spot it nested in the previous year when travelling to Ireland from their wintering grounds in South Africa?
Individual birds can be identified by marking them with light, numbered, metal rings fitted to their legs. Amazingly, scientific studies monitoring the movements of ringed birds found that there is a high level of nest faithfulness; many of the same birds do come back to the same nest.
Barn Swallows live for about ten years. On the transcontinental 10,000km journey from Africa, how they find their way back to the same nest in the same barn is unknown and must rate as one of the great mysteries of migration.
It is presumed that the birds reuse old nests as a means of saving the considerable amount of energy involved in building from scratch. Recycling also means getting off to a head start laying eggs and rearing their family.
Old nests are rejected if they are seriously damaged, infested with mites or beyond repair. Otherwise they are cleaned out, patched up and sparsely relined with soft feathers.
If they have to start from scratch, both parents cooperate in building the nest. They collect pellets of damp mud in their bills and plaster them together to fashion a shallow, half-cup stuck to a wall or timber beam. Well over 1,000 pellets may be needed so it is laborious work. The mud is reinforced with grass and other plant fragments.
Early-arriving Barn Swallows easily rear two broods during the summer. If all goes well a third brood is very possible so it pays to get off to an early start.
How Barn Swallows find their way back to the same nest in the same barn must rate as one of the great mysteries of migration.