Variable Sunbird’s nectar-thieving shenanigans exposed
NAIROBI, KENYA — This morning, I watched a spectacular male Variable Sunbird (Cinnyris venustus) feeding on the garlic vine (Mansoa alliacea) that’s blooming in our back garden.
But I noticed something odd. The sunbird, a nectivorous species, was visiting the base of each flower in turn:
The garlic vine (named for the odor emitted by its leaves when broken) is an ornamental plant introduced from the Neotropics. It’s in the family Bignoniaceae, which also includes Catalpa and the North American trumpet vine, Campsis radicans. Like the latter species, this plant has long, tubular flowers, and the Variable Sunbird (despite its elongated bill and long tongue) can’t possibly reach the nectar inside.
At least, not through the front door. But this is a clever bird — just look at that glint in his eye:
The bird was slipping his bill beneath the flower’s calyx and piercing the base of the corolla. Then, presumably, he could easily reach the nectar with his specialized tongue.
This behavior is called nectar thievery or nectar robbing because the plant may not get pollinated when its reproductive structures are bypassed in this way. (But see Are nectar robbers cheaters or mutualists?) Various sunbird species are known to engage in this behavior when needed (see, for example, the mention in Jewels of the bird kingdom from a newspaper in India), and of course the Neotropical flowerpiercers have specially hooked upper mandibles that let them specialize in a life of nectar thieving.
This next shot isn’t great, but it shows the Variable Sunbird’s threadlike tongue.
I went back later to examine the flowers and found tiny slits, the edges of which had started to brown: