Pollination is an important process in the scheme of things in Nature. Plants go to great lengths to achieve this – wind, animals, bats, birds, water and insects have all been used. Both plants and birds have co-evolved to mutually benefit each other for food and reproduction. The birds that are specially evolved for ornithophily (process of pollination of a flower by birds) are the Hummingbirds (Trochilidae) seen in the American continents, Honey-eaters (Meliphagidae) seen in Australia and Sunbirds (Nectariniidae) in the areas falling between, and a few others. These species are of different lineage and different areas, but the adaptation of the analogous structures driven by the common functionality gives rise to what is called as a convergent evolution.
While all of these are important, here we will look only birds that are equipped and are specially adapted to perform this task – the sunbirds. Sunbirds are a group of small sprightly birds with their size ranging between 10-22 cm. They are diurnal and many have bright iridescent colours. However, the most important characteristic is their down curved beaks, which in some species exceeds the length of the head.
The family Nectariniidae comprises of sunbirds and spiderhunters. There are 131 species worldwide and 15 species that occur in India and 6 in Karnataka.
Sunbirds can be seen in a variety of habitats. Many have even adapted well to human habitation. The species that we will be dealing with in this article are the one that are found in Karnataka viz.
Purple-rumped Sunbird, (Leptocoma zeylonica)
Vigor’s sunbird or Western Crimson Sunbird, (Aethopyga vigorsii)
Purple Sunbird, (Cinnyris asiaticus)
Crimson-backed Sunbird or Small Sunbird, (Leptocoma minima)
Loten’s Sunbird, Long-billed Sunbird or Maroon-breasted Sunbird, (Cinnyris lotenius)
Little Spiderhunter, (Arachnothera longirostra)
A resplendent male Loten’s Sunbird.
A pretty little Crimson-backed Sunbird.
Sunbirds are sexually dimorphic. The males are very colourful while the females and young are dully coloured. Among spiderhunters, both sexes are alike. They are known to aggressively defend their territory, either singly or in pairs.
Purple-rumped Sunbird male and female.
Loten’s Sunbird male and female – notice the long beak!
These birds are usually found feeding on the nectar of brightly coloured flowers, either hovering, or perched. Their light weight and strong wings give them the ability to hover with precision.
The Little Spiderhunter.
A Little Spiderhunter hovering with ease.
A Purple-rumped Sunbird nectar-hovering.
However, they resort to feeding on insects or worms during the breeding season either to sustain their increased need of proteins, or to keep up with the constant demand of food by their offspring.
Purple-rumped Sunbird with insects(?) in its beak.
Female sunbird feeding its chick. Sunbird young ones are brought up on a diet of protein rich insects.
Sunbirds and spiderhunters are highly adapted to feed on nectar. They have a long bill, curved and sharp, almost as long as their body. Males tend to have a longer bill than females do, which means longer flowers can be accessed, which in turn enables them to access a wider variety of flowers. The sunbirds have a long tongue. It is tubular with a split tip.
When the bird takes its bill into the corolla of the flower and extends its tongue, the grooves along the tongue provide for the capillary action automatically obtaining nectar without spending too much energy. When the bird is drinking nectar, it seems like it is lapping up nectar. High-speed photography has revealed that the tubes open down their sides as the tongue goes into the nectar, and then close around the nectar, trapping it so it can be pulled back into the beak.
The long tubular tongue of a sunbird.
The length of the bill vs the length of the body.
The length of the beak determines what kind of flower the bird can access.
Sunbirds have two kinds of plumage – breeding and eclipse. In their breeding plumage, males become very colourful and iridescent. Some species even have a yellow and orange tuft of feathers (pectoral tuft) on either side of each wing. During courtship displays, the male raises its head, fans its tail and flutters with partly open wings that expose the pectoral tufts and sings before the female. It is also observed that in some species, the pectoral tufts are intentionally exposed even while sleeping. Eclipse plumage is during the non-breeding seasons. The males revert to looking dull like females, but with remnants of breeding plumage in patches or with a dark line running down from the throat and chest in the middle.
A Purple Sunbird male in eclipse plumage.
A Loten’s Sunbird displaying the tuft of pectoral feathers.
Like the Loten’s Sunbird, the male Purple Sunbird also displays pectoral feathers.
The gaudy Vigor’s Sunbird.
Sunbirds are seasonal breeders, usually during the wet seasons. Some species are capable of breeding throughout the year and some raise two broods a year. Sunbird nests are purse-like, often hanging from a thin branch. They are built with vegetation, dried bark, grass, lichen and bound together with of plenty of cobwebs. Generally, females build the nest, assisted by males. The clutch consists of two to three eggs that are incubated by the females. Spiderhunter nests are not conspicuous. They are small and are attached like a cup under broad leaves like that of the banana plant. Only the females build the nest but incubation is shared by both the sexes.
Be it forests or urban spaces, sunbirds can be seen. Do watch them go about their routine and you will not be disappointed.