Cuckoos are hard workers

CUCKOOS, the first of the migrant birds to leave our shores in the Autumn, are packing their bags.

Some are gone already and virtually all adult ones will have left by the end of the month. Youngsters hatched this year will follow them in September. According to the Migration Atlas, our cuckoos travel inland through Europe, down the spine of Italy, and across the Mediterranean to Africa.

Adults are difficult to catch and nests with young cuckoos in them hard to find, so few cuckoos are ringed. This means that we still don’t know where in southern Africa our birds go. A juvenile recorded in Cameroon is the only cuckoo ringed in Britain or Ireland to have been found on the Dark Continent. A Dutch-ringed cuckoo, also a juvenile, visited Togo.

But why do adult cuckoos leave Europe so early in the autumn?

Shouldn’t they take it easy after the stresses of breeding, as other birds do?

The answer is that they’ve already had their holidays. If you abdicate your parental responsibilities the way cuckoos do, you have most of the summer to entertain yourself. Birds must grow a new set of flight feathers every year; the old ones become worn and tatty. Adults of most species do so before migrating, but the cuckoo travels first and moults in Africa. It makes sense to head off early, before the flight feathers get too frayed.

So is the cuckoo a dosser who sponges on other birds to fund a laid-back lifestyle and is too lazy to bother moulting before the big trip?

No, cuckoos work very hard indeed during a few frenetic weeks in late spring.

The first ones arrive here in April. The famous cuckoo song is delivered by the male. It’s function is a little obscure. He may be proclaiming a territory, but cuckoo territories are rather loose and ill-defined.

It’s the hen cuckoo who needs a territory. She must spy on, and really get to know, her neighbours, the little songbirds in whose nests she will lay her eggs. In Ireland, the host of choice is the meadow-pipit, known in Irish as Banaltra na Cuaiche, the ‘Cuckoo’s nurse’. Irish cuckoos produce eggs coloured like those of pipits. Cuckoos elsewhere target other species and their eggs match those. The reed warbler, not that common in Ireland, is much favoured in south-east Britain. Eggs have been recorded in the nests of over a hundred European species.

Locating up to two dozen nest-building pairs of pipits is a formidable task. Choosing good vantage points, on telephone wires or branches of trees, the cuckoo watches the to-ing a fro-ing of her potential victims. She bides her time; an egg, ideally, should be laid when the hostess has started laying, but has not completed, her clutch.

Laying is an impressive piece of choreography. When the victims are away feeding the cuckoo swoops in. Gripping the rim of the nest, she lifts one of the eggs, lays her own and leaves. The entire operation takes about 10 seconds. She eats the stolen egg; the nutrients help to form her own ones. It’s not quite true to say that a cuckoo doesn’t incubate.

The egg undergoes a few days development in the mother’s oviduct before it is laid. This head-start usually means that it hatches before the host’s eggs do. The naked reptilian chick has a sensitive back. Other eggs pressing against it irritate the interloper so it stretches out its limbs and pushes backwards until all of the host’s eggs, or chicks, topple over the side of the nest. Soon the usurper is alone and the duped foster parents exhaust themselves bringing copious quantities of food to it. The impostor may be six times heavier than they are by the time it leaves the nest.

But the youngster now faces a formidable challenge. All alone, relying entirely on instinct, it must make its way to Africa. There is no parent or nanny to offer advice and no Fás training course to help it get started. The cuckoos has the ultimate Global Positioning System.