First described in 1873 by Allan Octavian Hume, the Narcondam Hornbill (Rhyticeros narcondami) remains as much an enigma as it was when first spotted. As Hume’s ship approached the island, the large white-tailed birds seen flying from tree to tree were mistaken to be Nicobar pigeons that the party had been seeing a lot of. The notion was quickly dispelled when they realized that the tails and necks of the birds they were looking at were much longer; this was no pigeon. That this was a hornbill was the last thing anyone could’ve imagined, since there are no hornbills found anywhere else in the Andaman archipelago.
Of the 62 species of hornbills found in the world, Narcondam Hornbill has the smallest global geographic range (view the Birds of the World species account here). It is found only on Narcondam, a tiny 6.82 km2 island of volcanic origin that lies to the north-east of the main Andaman and Nicobar archipelago in the Indian ocean. Now extinct, this island is part of the subduction arc that runs down through Sumatra and Java and has formidable volcanoes like Toba and Krakatoa.
While the various archipelagos of southeast Asia have a number of hornbill species, the closest relative of the Narcondam Hornbill – evolutionarily, the sister species – is the Papuan Hornbill (Rhyticeros plicatus) found right at the far end, in Papua New Guinea and the adjoining islands of the Moluccas, Bismarck Archipelago and Solomon Islands, at the edge of the Pacific ocean. The Narcondam Hornbill is half the size of the sister species. That it shrunk in size after it took up residence on the island is quite probable, though how it came to be there in the first place is open to speculation.
Recent population estimates for the Narcondam Hornbill had put their numbers at around 1,000 birds; that means an unimaginable density of 150 birds per sq. km. Nowhere else in the world do hornbills occur at such high densities. What would a forest that could sustain hornbills at such high densities look like? I was part of a team of researchers who went to the island last winter to find out first hand.
Islands usually host simplified networks of communities – with fewer fruiting trees, for instance, and fewer frugivores – when compared to mainland sites. Over two months, we estimated the abundances of all the important frugivores on the island and the densities of fruit trees. While we confirmed the high densities of hornbills, we also found that the density of the fruit trees, especially that of figs, was anywhere between two to ten times as high as their density in comparable forests that harbor hornbills.
Effective dispersal drastically improves the chances that a seedling will mature into a tree, therefore, not only do frugivores help maintain viable populations of fruiting trees, they effectively shape the forest that they live in.
Work by some of our team members in northeast India, in forests that have up to five species of hornbills, has shown that hornbills are dispersers par excellence, widely dispersing seeds that they drop unscathed, in a veritable ‘seed rain’ (Naniwadekar et al. 2015) of up to 10,000 seeds/ km2/ day – a feat that has earned them the epithet ‘farmers of the forest’. And this when they occur at densities of only 90 birds/km2 (Naniwadekar and Datta 2013).
Being the largest and most abundant frugivore on Narcondam, the eponymous hornbills have inadvertently tweaked the distribution of trees to favor the ones that they devour; this has become their very own garden of Eden.
Listen to Narcondam Hornbills in the forests of Narcondam (Macaulay Library 151625301).
Sartaj Ghuman is a wildlife biologist who prefers poetry to academics. When not collecting data in the field, he divides his time between gallivanting in the mountains and masquerading as an artist. Contact info: email@example.com.
The work on Narcondam Island is part of a collaborative project that would not have been possible without the support of the Andaman and Nicobar Forest Department, the Special Armed Police (SAP) and the Coast Guard. You can find out more about the project here.
As part of a collaboration with:
Bird Count India is an informal partnership of a large number of Indian organizations and informal groups, all of whom share the goal of better documenting and monitoring India’s birds. The partnership conducts workshops and birding challenges and encourages birdwatchers to document their observations on the eBird India portal (ebird.org/india).
Art credits: Sartaj Ghuman