Leaving behind the village with its open fields baking in the sun, we head for the forest. Summer in Assam can be scorching, but the liana-draped trees — some more than 40 m tall — cast deep shadows and the thick forest floor, cool and alluring, beckons us with paths of squelching mud. The dread of ticks and leeches forgotten in the thrall of birdcalls, we enter Dehing Patkai National Park. This is amongst the northernmost tropical lowland evergreen rainforests in the world. Though the links are now tenuous at best, this forest once stretched unbroken from the foothills of the Himalayas to the coast of Vietnam.
As we walked deeper into the forest, the outside world began to feel like a dream. Then we heard a thin, inflected whistle, like a raptor’s call. A heartbeat later, an answer to it, and then another! It was a flock of white-throated brown hornbills or Austen's brown hornbill (Anorrhinus austeni), and they were coming our way. Of the nine species of hornbills found in India, brown hornbills are perhaps the least known, and they call this forest and the area all the way to the coast of Vietnam their home.
Brown hornbills live in flocks of 4-8 birds, and the flock is thought to comprise a breeding pair and the offspring from previous years. These latter will help raise the chicks by joining the male in bringing food to the female sealed inside the nest. Cooperative breeding is seen in quite a few hornbills and many other bird species, the best known of which are jungle babblers, whose case of group living has earned them the epithet of “seven sisters”. Brown hornbills are then the “seven sisters” of the high canopy.
All hornbills nest in tree cavities. They don’t make these cavities themselves. Older cavities from branch-fall or ones that woodpeckers have made in the past are found and cleaned. Cleaning the cavity is an important part of the courtship. Another part of the courtship is that the male regurgitates fruits to feed the female — a promise of fidelity and a steady food supply for the next three months she will spend in the cavity.
After mating, the female enters the nest and seals it from the inside using her faeces, which hardens like clay, leaving just a thin vertical slit through which the food is passed on to her and the growing chicks. Typically, two, rarely three, eggs are laid, and the chicks’ survival depends on how well they are fed. This is where the story gets even more interesting for brown hornbills — for they are cooperative breeders, and the parents have a posse of assistants in the flock helping them out.
Lohit, a tributary of the Brahmaputra, marks the northwestern limit of the brown hornbills’ distribution. They prefer dense forests with good canopy cover, and even here, their densities are typically low. And while most hornbills predominantly eat fruits, supplementing their diet with animal matter, brown hornbills are partial to non-vegetarian fare — caterpillars, katydids, mantises, spiders, frogs, and even small birds and rodents that weren’t quick enough to escape, are all fair food.
“Foraging for such an assortment of viands results in a movement pattern that’s very different from other hornbills”, says Dr Rohit Naniwadekar, a senior scientist with Nature Conservation Foundation who has been studying hornbills for over 18 years. “While other hornbills keep track of fruiting trees and will spend time on or around trees with ripe fruits, brown hornbills generally forage in the canopy like a hunting party, always on the move.”
As we walked through the forest of Dehing Patkai, the hunting party of brown hornbills had just returned home, and we had the opportunity to observe their behaviour. What we saw was similar to this series of images photographer Dhritiman Mukherjee captured in the same forest at another time.
Silently, we waited and watched, craning our necks, scanning the canopy. And suddenly, quiet as a thief, a bird appeared on an ironwood (Mesua ferrea) tree before us. A long glide, a perfect landing and wings folding in the blink of an eye left us feeling like we’d just witnessed a magic trick: one moment the branch was bare, the next, the bird was sitting with wings folded, prim as ever.
The relatively large casque on the bird’s beak told us that this was an adult male. It had what looked like a grasshopper in its beak and took its time scanning the surroundings. We were well hidden, and it did not see us. We saw it hop, jump, take a short flight and land near the nest. A low cackling sound emanated from the nest, and the grasshopper was passed to an eager beak that emerged through the slit.
Hunting practices that target the nest remove the young and the breeding females. No species can withstand pressures of that sort. Another threat is habitat loss and fragmentation. The brown hornbill is listed as “Near Threatened” on the IUCN Red List. Every time a new highway cuts through their habitat or a new oil pipeline is laid, the forest that is their home shrinks further, and their habitat — like a finely woven rug — begins to fray and then unravel at the edges.
We need better protection of the existing rainforest fragments and ecological restoration of the many degraded patches of this landscape. The restored patches can act as corridors not only for the hornbills but also for gibbons and elephants that share this space and will help preserve the biodiversity of this unique ecoregion for coming generations.
About the contributors
Sartaj Ghuman
Dhritiman Mukherjee
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