Nectar gives songbirds high-energy lift on long-haul migrations from Africa

Nectar, according to classical mythology, was the drink of the gods. Now scientists have discovered it is the fuel that turns some of Britain's best-known songbirds into epic flying machines.

Nectar, according to classical mythology, was the drink of the gods. Now scientists have discovered it is the fuel that turns some of Britain's best-known songbirds into epic flying machines.

Warblers, which fly thousands of miles from Africa to Britain each spring, stop off in the islands of the Mediterranean to replenish their energy reserves with nectar, says research in the latest edition of Ibis, the British Ornithologists' Union journal.

American hummingbirds have long been known to feed on nectar so that they can maintain a phenomenal 70 wingbeats per second. But the fact that garden warblers and blackcaps, which mainly eat insects in summer and fruit in autumn, rely on nectar to complete their migratory journeys was not known before the study by researchers from the Swiss Ornithological Institute.

They studied the eating habits of these two species, plus the whitethroat, another common summer visitor to Britain, and the subalpine warbler on Ventotene Island off Naples, after their arrival from tropical Africa.

The birds were found to be foraging for nectar on the two most common flowering plants, giant fennel ( Ferula communis) and a Brassica species. Birds captured as part of the research, and placed in cages with dishes of mealworms and artificial nectar in plastic flowers, showed a "striking preference" for the sugar mixture.

Dr Humphrey Crick of the British Trust for Ornithology, who is an Ibis editorial panel member, said: "This significantly new finding helps explain how birds, after long flights, are able to quickly 'refuel' to continue north to their breeding territory."

He explained they built up fat reserves through fruit consumption before leaving their winter quarters in spring, and berries also sustained them during their autumn return to Africa.

"But fruit isn't available when they break their spring journeys on Mediterranean islands and pursuing insects would use up what little energy they have left, so nectar is clearly an ideal first food during such stopovers," Dr Crick said. "This could have global warming implications. If climate change leads to the plants involved flowering earlier, it could affect the availability of this important food and therefore have an impact on the migration of these birds."

Islands off southern Europe, more than 2,000 miles north of tropical African regions where many warblers spend their winters, provide vital breaks after non-stop flights across the Sahara and Mediterranean.

The Ibis report says: "Birds during long-distance flights not only deplete their fat reserves but also burn a considerable amount of protein. This leads to reductions in the mass of different organs, most prominently in breast muscle, gut and liver."

That prevents migrants from restoring body energy efficiently at the start of a migration break. Alongside their need to recover from "fuel depletion", nectar could be an ideal food for these flight-weary warblers.

The researchers believe nectar helps to stop their protein stocks breaking down quickly and restores muscle glycogen, "a fuel store indispensable for anaerobic exercise such as short-burst and take-off flights for hunting mobile prey or escaping predators.

"Birds not only need to replenish their energy reserves and replace lost protein, but might also require rest and sleep. Uptake of nectar - high in energy and easily obtainable - may also be a way to save time needed for rest and sleep."