There are 57 different species of hornbill in the world, nine of which live in Khao Sok National Park. Hornbills are characterized by a long, downcurved bill with a casque (horn) on top. The casque is hollow and serves no known purpose, although they are believed to be the result of sexual selection. Males are usually larger than female hornbills, weighing up to 17% more and having a greater wingspan. Great Hornbills have a wingspan of about 1.5 m, making them Khao Sok’s largest birds! The height of hornbills can range from 30 cm to 1 m (without counting their tail). Hornbills can live up to 30 years of age, and are mostly black and white in color with some yellow and red usually on their casques. Most species are classified between ‘lower risk’ and ‘near threatened’ by the IUCN. The Great and Helmeted Hornbills are listed in appendix I of CITES, since the casque can be used as a carving material, similar to ivory.