Great Hornbills are similar to that of Rhinoceros Hornbills, with the Male being larger and measuring 121-150cm in length, and the female measuring 112-125cm in length. The males have an average weight between 2.6-3.9kg, and the females have an average weight between 2.1-3.4kg.
The Great Hornbill is a very large hornbill species. They have a black band across a white tail and black wings with a white trailing edge. The head has some white plumage areas, as well as the neck, wing coverts and base of the tail, all of which are usually cosmetically stained yellow with preen oil.
To distinguish males and females apart, you look at the eye and orbital skin, the same as in Rhinoceros Hornbills. The males have red eyes with black orbital skin, and a flat casque that is forked at the front with black edges. The females have white eyes with red orbital skin that flushes brighter when breeding. The females have a smaller casque that lacks the black lines. Juveniles have blue-grey eyes and have a casqueless bill, it takes over five years for them to grow to maturity.
The Great Hornbills produce a loud reverberating call with a kok sound. Pairs with often duet this call and it can be heard over 800 metres in the forest. They also produce other guttural sounds.
The Great Hornbill distribution is spread over south-west India, south Himalayas and south China into Indochina south to Peninsular Malaysia and Sumatra.
Their preferred habitat is primary evergreen and moist deciduous forest. They occur at sea level, but their preference is hills further inland that are between 600-1,000m in elevation. They have been recorded up to 2,000m in the Himalayan foothills and in northern Thailand.
They feed in the canopies of large trees and will be found in a resident pair or family group. They are largely sedentary birds, although they will range for food outside of breeding season. They are known to roam widely in a search for fruiting trees, and they have been seen flying over open areas on occasion. Flocks may gather in fruiting trees or in evening roost spots; there was a recording of over 200 individuals on one occasion before 1927. They will sometimes fly down to the forest floor to retrieve fallen fruits.
Figs are a favourite food of Great Hornbills, although they will also take other fruits that are usually lipid-rich. They are also known to take animal prey such as small mammals, birds and reptiles, and they will also take large insects and other arthropods; they have also been recorded taking flowers and buds. They have a hunting behaviour which is displayed as hopping along branches and poking their large bills into crevices and bark – once they grab the prey, they will toss it in the air and catch it again for a better grip.
Surveys have been taken on different populations a number of years ago to discover the proportion of each food group in the Great Hornbills diet. In Khao Yai National Park in Thailand, it was found that 57% of the total food weight was figs, 29% was other fruits and 14% was prey. A survey during the breeding season showed that there was a food delivery of 30.5g of food delivered per hour.
Another study in southern Thailand found that 54% was figs, 41% was other fruits and 5% was animal prey, with 47g of food brought to the nest per observation hour.
In India, three fig species dominated the diet, which became even more prevalent in the non-breeding season as lipid-rich fruits became few and far between.
They have been recorded to live up to 41 years in captivity and up to 30 years in the wild.
Great Hornbills have a heavy and laborious flight pattern which involved 3-4 flaps (heavy wing beats) and a long glide; the wings make a loud whooshing sound.
The nesting season of Great Hornbills runs between January to June throughout its range, this species is monogamous and territorial. They become more vocal during the breeding season, making a loud and slow kok call. There have been rare recordings of aerial casque-butting. There preferred nesting trees are various hardwood species and they use a cavity that is on average 6-45m above the ground – the height of the nest is dependent on forest type. The female will enter the nest and seal herself inside; faeces will mainly be used to create the plaster for sealing the nest. Chewed wood, bark and food debris may also be used in conjunction with faeces for sealing the nest, little or no soil will be used. A vertical slit of 20cm long and 5cm wide will be left open.
They can lay between 1-4 eggs, although it is most usually 2; the eggs will be laid with a 4-5 day interval in between and have an incubation period of 38-40 days. The male will bring around 30g of food per hour to the nest for the female and her chicks. The male will usually make around 3-5 visits to the nest per day with the visits starting late morning and lasting 15-20 minutes; visits with animal prey are shorter. The male can deliver up to 185 items of food a day, with recordings of up to 50 grape-sized fruits in one feeding. The male will regurgitate them individually from his gullet.
Once the chicks have hatched, the amount of food delivered increases exponentially, but the number of visits will not increase. The male will forage a forest area of 1.3-4.5km2 around the nest and will fly up to 3km away.
The female will emerge when the chick is 14-59 days old, it is around 85 days on average (with the range being 62-121 days) after sealing herself in the nest. After the female has emerged, she will help the male with the feeding of the chicks. The chick will reseal the entrance of the nest and will fledge at 72-96 days. The total nesting period in the wild is between 102-144 days – it is shorter in captivity.
The biggest threats to Great Hornbills include habitat loss, especially areas of forest with large trees that typically may be targeted by loggers, which in turn takes out their preferred nesting trees. The forests are illegally logged and cleared for land conversion, mainly for housing and agricultural development. Agricultural developments include small-scale agriculture to large-scale plantations. They are also facing illegal hunting, and due to their predictable behaviour, regularly visiting the same feeding sites as well as using the same tree-cavities to nest in, they are easily targeted by local hunters. They are most usually hunted for food as well as for the casque and tail feathers, which are used as adornments by local communities. It is also highly prized for its fat, which is used for a variety of purposes ranging from medical treatments to gun polish. Great Hornbills are also captured for the pet trade, with chicks being collected in south India and Thailand and may also be taken as ‘bycatch’ by hunters targeting Helmeted Hornbills Rhinoplax vigil.