Bako National Park records eight species of hornbill — an extraordinary concentration for a 27 km² reserve. The rhinoceros hornbill (Buceros rhinoceros), Sarawak's state bird, is the most iconic and is genuinely common here. Its call — a deep, resonant duet between pairs — is one of the defining sounds of Bako mornings, audible from the park headquarters before dawn. A bonded pair maintains a territory of several square kilometres and typically nests in a large hollow tree, the female sealing herself inside with mud and droppings for the entire incubation period while the male feeds her through a narrow slit.
The rhinoceros hornbill's casque — the bright orange-red structure above the bill — serves as a resonating chamber that amplifies its calls. The casque is solid keratin (unlike the hollow casques of some species) and continues growing throughout the bird's life. Adult males have deeper, more developed casques than females, and the casque is used in aerial jousting between rival males. At Bako, these jousting flights — two birds colliding bill-to-casque in midair above the canopy — are occasionally witnessed over the open padang on the Lintang Trail.
Beyond the rhinoceros hornbill, Bako's hornbill list includes the bushy-crested hornbill (the most frequently seen, often in noisy groups of 6–10), the wreathed hornbill, the black hornbill, the Oriental pied hornbill (small, common near headquarters), the helmeted hornbill (rare, with a solid ivory casque, the most traded bird product in the illegal wildlife market), the white-crowned hornbill, and the white-throated kingfisher-like dollarbird, which is sometimes grouped with the hornbill assemblage in Bornean birdwatching lists.
The best times for hornbill watching at Bako are 06:30–09:00 and 16:00–18:00, when birds are most vocal and active. The open kerangas plateau on the Lintang Trail and the fruit-bearing trees around park headquarters are the most productive locations. When a fruiting fig is found within the park, all eight species may converge on it simultaneously — ask the park rangers whether any figs are currently in fruit on your arrival day. Binoculars (8x42 minimum) are essential; the birds move fast through the canopy and distances are considerable.