Brood­ing Barn Swal­lows get off to an early start

Bray People - - LIFESTYLE - JIM HUR­LEY’S

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.

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