London, Apr 14 : Just like American hummingbirds, African sunbirds have also learnt to hover around a flower to collect nectar, and scientists have found that the tree tobacco plant prompts the birds’ ability to hang around.

Tree tobacco, the South American plant has made its way to South Africa, where sunbirds pollinate it.

The plant produces yellow, tubular flowers and like other plants with flowers of this shape, it depends on nectar-sipping birds for pollination.

In its native South America, tree tobacco is pollinated by hummingbirds, which have evolved the highest metabolism of any animal in order to generate enough energy to hover over flowers for long enough to drink their nectar.

However, to the astonishment of evolutionary biologists, there are no hummingbirds outside the Americas.

Native Old World plants with tubular flowers usually produce some sort of perch to allow birds to sip their nectar.

Sjirk Geerts of Stellenbosch University in Matieland, South Africa, noticed native malachite sunbirds hovering around tree tobacco flowers in northeastern South Africa, and decided to investigate.

Although the birds were known to hover occasionally before, but it was found that some sunbirds are now getting most of their winter food from tobacco tree flowers.

"This is the first time we have observed them making a lifestyle of it," New Scientist magazine quoted Geerts as saying.

Earlier, the sunbirds used to migrate out of the region in winter because there was no nectar, but now they stay put.

Despite its impact on sunbird-pollinated plants elsewhere, or on sunbird numbers is not known, the researchers reckon that tobacco plant is benefiting.

The researchers put netting over some tobacco trees, and found that plants pollinated by sunbirds set three times as much seed.

The discovery sheds a new light on why hover-feeding evolved in birds in the Americas but not elsewhere.

Geerts now wants to find out if sunbirds keep hovering during the summer, when they are expending most of their energy on raising young. (ANI)