Factors Affecting Decline
Several factors have contributed to this species' decline. For one thing, habitat destruction such as logging for rubber plantations has encroached upon the native forest, and while more sustainable forest uses by humans are tolerated well enough, monocultures are of little use to this island endemic and are utilized only infrequently. An increasing human population has resulted in much clear-cutting in the mid-late 20th century, and expansion of military installations in these frontier islands has also resulted in considerable habitat destruction.
Also, the Andaman Red-whiskered Bulbul (Pycnonotus jocosus whistleri) was introduced to Camorta by the British; it was later brought to other islands in the Nancowry group by locals, who, like many people elsewhere, consider the Red-whiskered Bulbul a popular pet. The two bulbuls presumably compete for food, nesting locations and other resources, and if the human-assisted P. j. whistleri is not actually displacing H. virescens, being well-established on Katchall, Nancowry, Teressa and Trinkat it is certainly keeping the Nicobar Bulbul's population lower than it could be. On the other hand, there is no reason to suppose that the native species is an inferior competitor; rather the two bulbuls' populations soon seem to reach an equilibrium: on Katchall the Red-whiskered Bulbul was established in the 1910s or so already, and this has not prevented healthy Nicobar Bulbul stocks from persisting on that island to our time.
The Nicobar Islands were hit hard by the 2004 Indian Ocean tsunami, and the central group was perhaps most severely affected, with at least hundreds, maybe thousands of its inhabitants dead. On Katchall there was perhaps the highest loss of life in the entire Nicobars, but this was to catastrophic destruction of settled areas and much of the island's interior forest was not affected. Trinkat was literally torn into three pieces, while on Camorta flooding was extreme in the northern part only. Nancowry on the other hand suffered rather little damage overall. On Teressa, the low-lying plains suffered extensive flooding, bisecting the island in fact, but the remaining forest fragments are mostly confined to the hills and were spared. Bompoka and Tillanchong, though small, are quite steep and consequently were not much affected. Though the effect of the Nicobar Bulbul's population on Trinkat for example might have been devastating, the tsunami is not known to have significantly harmed the overall stocks of the species.
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