The purple-rumped sunbird is a small nectar-feeding bird endemic to the Indian subcontinent. While the females are dull-coloured, males are flamboyant, with blue, green, crimson, purple and yellow hues.
The purple-rumped sunbird (Leptocoma zeylonica) belongs to the family Nectariniidae, consisting of sunbirds and spiderhunters. Sunbirds are small nectar-feeding birds with curved beaks that come in a vibrant colour palette. These species are largely distributed across Africa, Asia and northern Australia. They look quite similar to other nectar-feeding bird groups – hummingbirds from the Americas and honeyeaters in Australia, but are distantly related to them. There are about 145 species of sunbirds, of which around 13 species are found in India across a diverse range of habitats. Of these, the purple-rumped sunbird is widely distributed in peninsular India and is a common sight in gardens, where it hardly ever stays still, hopping from one flower to the next. While the females are dull-coloured, males are flamboyant, with a metallic blue-green crown, iridescent purple throat, crimson back and chest, green shoulder patches, a barely visible purple rump and a pale yellow underbelly.
Female preference for brightly coloured mates has driven the evolution of a wide gamut of vibrant colours in sunbirds. The opposing forces of selection for conspicuous colours driven by mate-choice and natural selection for cryptic colours to escape predation have led to contrasting plumage in male and female sunbirds. Similar to butterflies, sunbirds get their colours either from pigments like melanin and carotenoids or from nano-scale structures in their feathers made of keratin, melanin and air. Pigments absorb certain wavelengths of light to produce colour, while scattering of light from nanostructures can give rise to a wide range of iridescent colours. Scientists think that it may be evolutionarily easier to expand the palette of structural colours by small changes to these nanostructures. On the other hand , it is difficult to produce novel pigments that are tied to metabolic pathways and diet. Sunbirds produce colour by both these mechanisms, and the appearance of melanin-based colouration is associated with an increase in their species diversity.
Male sunbirds flaunt the vibrant colours on their upper body during courtship displays, where some species flash bright underwing tufts to woo females. When it comes to building a nest, the female of the purple-rumped sunbird does most of the heavy lifting. She uses cobwebs, plant material and other odds and ends to build a pouch-shaped nest with a portico that often hangs precariously from the end of a branch. “Grasses, fibres, fine roots, tendrils, fragments of bark, moss, lichen, petals or sepals of flowers, in short, anything that looks old and untidy is utilised as building material,” says the British ornithologist Douglas Dewar in his book, Glimpses of Indian Birds. “The completed nest, which usually hangs in a most conspicuous place, often passes for a small mass of rubbish that has been pitched into a bush.” The female lays two mottled eggs in the nest and incubates them and both the parents feed the hatchlings.
Purple-rumped sunbirds pollinate plants when they dip their head into the flower tube to reach for nectar using their slender brush-tipped tongues. But when nectar is out of reach, they sometimes cheat by poking a hole from the side at the base of the flower. They usually perch while drinking nectar from flowers, sometimes even upside down, but can also hover in the air while they feed.
The purple sunbird (Cinnyris asiaticus) and the Loten’s sunbird (Cinnyris lotenius) are other common sunbird species seen in southern India. On the IMSc campus, I have seen sunbirds in bushes behind the flatlets and in the patch of shrubs behind the herb garden beside the guest house. I haven’t seen them around the main building side, though they are fairly common in most home and city gardens. Please write to us about spots on campus where you have seen sunbirds.
