Built-in bird perch spreads the pollen.

In a twist on seduction in the vegetable world, one South African plant grows a flowerless spear that lets avian pollinators perch within beak shot of the plant's flowers.

Naturalists proposed decades ago that this spear of the South African plant called the rat's tail (Babiana ringens) might work as a pollinator perch. To test the idea systematically, Bruce Anderson of the University of KwaZulu-Natal in Pietermaritzburg, South Africa, and his colleagues closely monitored flowers in the wild, leaving some of them as they were and removing the perches from others. The only pollinator seemed to be the malachite sunbird (Nectarinia famosa).

Male sunbirds were more than twice as likely to visit a plant with a perch and then to stay there four times as long as they would visit and stay at a perchless plant, the researchers report in the May 5 Nature. Female sunbirds didn't show a strong preference. Researchers speculate that males might especially favor perches to protect their tail feathers, which are longer than those of females, from the wear and tear of ground landings.

The plant's seed provided more evidence that the perches really matter to the plant. Plants without perches produced only about half as many seeds as plants with perches did, Anderson's team noted.--S.M.