Why the evolutionary link between flowerpeckers and mistletoes is crucial to the forests

The mistletoe is one of those little plants you hardly notice in the rainforest. It perches on branches of trees like a sea fan on a coral boulder, or like the Christmas decoration. At first glance, it seems like another tassel of twigs and leaves. But look closer and you will notice that its leaves are smaller and a paler green, tinged with coppery yellow, unlike the tree’s longer, parrot-green leaves.

On the tree’s brown branch, which is powdered with white lichen, the little plant arises out of a swollen bulb-like base, holding out dark brown twigs dusted with white spots, like chocolate sprinkled with sugar. Clusters of pinkish-red berries and buds line the smaller plant’s twigs, on the tree bereft of fruit or bud. The little plant is an epiphyte: it’s a plant that grows on other plants. It also shares a deep connection with a small bird. Together, they epitomise the irreplaceable vitality of the forest.

Undeserved reputation

Mistletoes are a partial parasite. They synthesise their own food through photosynthesis but their special roots draw water and nutrients from the host tree on which they are perched. Extreme infestation of trees by mistletoes is rare in natural forests, occurring more often in degraded or managed forests and monoculture plantations. Still, foresters and others concerned with production of timber or fruits from trees sometimes call for mistletoes to be removed or eradicated.

Recent research suggests that this may be unwarranted. In forests, falling mistletoe leaves add vital nutrients to soil under the trees where they grow. Experimental removal of mistletoes causes a decline in the soil’s nutrient and affects the population of other species.

Mistletoes sustain a large number of species worldwide – flowerpeckers, the barbet-like tinkerbirds of Africa, the mistletoebird and honeyeaters of Australia, the sunbirds and white-eyes of Asia, mouse lemurs and sifakas of Madagascar, tyrant and silky flycatchers and colocolo opossums of the Americas, the eponymous mistle thrush of Europe, myriad insects and other creatures.

A modest bird

You would hardly notice a flowerpecker in the rainforest – the bird is small enough to hide behind a leaf or to hold in a closed fist, and drab enough to escape the attention of anyone but an ardent birdwatcher. The undistinguished little bird is dull olive brown on top and a rather dingy white below, with a sharp, glinting, dark and attentive eye and a gently curved beak to poke among the flowers. A metallic, fidgety tick-tick-tick call announces her presence as she darts through the boughs. You have to be quick to spot her before she disappears.

I’ve traveled far from my home in the mountains of the Western Ghats in South India, to see this flowerpecker. And not just any plain flowerpecker, but a particular one: a bird flitting among the mistletoes on the same trees where I had seen the species two decades earlier.

I am seated on the steps of the Dampatlang watchtower in Dampa Tiger Reserve in Mizoram. To the south, steep cliffs plunge to Tuichar valley. An evergreen forest with hundreds of trees adorned with mistletoes surround me on three sides. Along the watchtower grow two small orange trees and a straggling Holmskioldia holding bunches of scarlet cup-and-saucer blooms. Against the wild forest backdrop, the planted orange and cup-and-saucers marked what seemed a very human temperament to cultivate and ornament the land we live in.

Bird’s eye view

Seated two stories high on the watchtower, I am almost eye-to-eye with the flowerpecker. The bird flits from branch to branch, dives into each mistletoe cluster, peeking, probing, seeking with eye and beak. Flowerpeckers remain closely tied to the mistletoes that grow on trees. Their territories span a few hectares at most. The birds consume mistletoe flower nectar and fruits, but this is a two-way relationship. The birds pollinate the plant’s flowers and disperse its seeds.

Mistletoes have tube-like flowers. When probed by a flowerpecker’s beak, these flowers part like a curtain or pop open, dusting the bird’s head and face with pollen. After the bird sips the sugary nectar with a special tube-like tongue (who needs a straw when your tongue can roll into one?) she flies to the next flower, rubbing off some of the pollen onto the flower’s receptive female parts, triggering the latter plant’s reproduction.

Despite the flowerpecker’s name, the birds remain fruit-lovers at heart. Mistletoes often have long and overlapping flowering and fruiting seasons so there is always food for a hungry flowerpecker to find. Ripe mistletoe fruit never fails to attract flowerpeckers.

Mistletoes represents a group of over 1,300 plant species worldwide belonging to five families, chiefly the Families Loranthaceae and Viscaceae. As the second name suggests, its fruit is viscid – a single seed is surrounded by a sticky pulp, often enclosed in a rind-like peel.

The plain flowerpecker and its close cousin in South India, the Nilgiri flowerpecker, manipulate mistletoe fruits in their beaks to gently squeeze the seed from the pulp. They swallow the sugary, nutritious pulp and wipe their bills on twigs to remove the sticky seed. If the flowerpecker swallows the fruit, the seed passes rapidly through the bird’s gut to be excreted out. To remove the still sticky seed, the birds wipe their rears on twigs or tree branches. In either case, these actions have the same result, which biologists call directed dispersal: the mistletoe seed gets planted where it is likely to germinate.

Feisty flowerpeckers defend their mistletoes, darting at intruders who entered their territories, chasing after them, zipping between branches with rapid ticking calls. Fighting flowerpeckers have been known to fall to the ground while grappling fiercely with each other. One imagines their raging little hearts beating furiously, as they flay and peck at each other to defend what they perceive as their own.

An hour later, I leave with the sense that there is more to this than just a symbiotic evolutionary link between bird and mistletoe in a forest webbed with ecological connections. Perhaps, behind the gleam of that flowerpecker’s eye, there resides, too, a desire to cultivate and protect what she consumes and an aesthetic to adorn the trees in her forest with the prettiest little plants she can find.

TR Shankar Raman is a scientist with the Nature Conservation Foundation, Mysore. His email address is: trsr@ncf-india.org