This species frequents wet evergreen and mixed deciduous forests, ranging out into open deciduous areas to visit fruit trees and ascending slopes to at least 1,560 m in south India (Mudappa and Raman 2009) and up to 2,000 m in Thailand (Poonswad et al. 2013). The abundance of this species tends to be correlated with the density of large trees, required for nesting, and it is therefore most common in unlogged forest (Datta 1998).In the breeding season, they are largely sedentary moving in a small area but in the non-breeding season they range widely (Poonswad and Tsuji 1994, Naniwadekar et al. 2019). Known nest trees include Tetrameles nudiflora, Dipterocarpus gracilis, Dipterocarpus turbinata, Cleistocalyx nervosum, Shorea faguetiana, Hopea odorata, Neobalanocarpys heimii, Palaquiuum ellipticum, Mangifera indica, Bombax ceiba, Mesua ferrea, Syzygium gardneri, Koompassia excelsa (R. Naniwadekar and A. Datta in litt. 2016). It has also been reported to nest in the non-native tree Grevillea robusta (R. Naniwadekar and A. Datta in litt. 2016). In general, habitat-use seems to be negatively associated with human population (A. Datta and R. Naniwadekar in litt. 2018). In the Anamalai Hills in southwest India, Great Hornbills are known to occur in and breed in shade-coffee plantations adjoining continuous rainforest tracts, where large nest trees and food trees (like Ficus spp.) are retained in the plantations (Pawar et al. 2018). In this same population, the estimated percentage of breeding Great Hornbill pairs was higher (56%) in the contiguous protected forests than in the adjoining shade coffee plantations (33%; Pawar et al. unpubl. data)
Food species include Ficus spp., Polyalthia sp. and Elaeagnus sp. (Kaur et al. 2015). Figs comprise a major part of the diet (Kannan and James 1999, Datta and Rawat 2003, Naniwadekar et al. 2015b) but the species also takes eggs, amphibians, reptiles, insects, mammals and small birds (Kemp and Boesman 2017). They also feed on drupaceous fruits of Annonaceae and Lauraceae and arillate dehiscent capsular fruits of Meliaceae and Myristicaceae. The breeding season begins in March in northeast India, and between December and January in other parts of the range; throughout, the nesting period lasts around four months (Poonswad et al. 2013). Most  nesting hornbills produce one chick. The average nesting period is about 120 days (range: 102-144 days) (Poonswad et al. 1987, 2013). The chick hatches out of the eggs about 40 days after the female entry in the nest (Poonswad et al. 2013). The nest cavity is mostly an elongated slit in the tree (Poonswad 1995, Datta and Rawat 2004, James and Kannan 2009). It has been also reported to nest in non-native tree species like Grevillea robusta (Pawar et al. 2018). As the female is incarcerated and dependent on the male during this time, home range size is considerable smaller (0.7 - 7 km² [Poonswad and Tsuji 1994, R. Naniwadekar and A. Datta in litt. 2016]) than during the non-breeding period when it has been recorded as 138 km² in Thailand (Keartumsom et al. 2011) and c. 50 km² in northeast India (R. Naniwadekar and A. Datta in litt. 2016). 
In Malaysia, there are very few nesting records to date, with only reports from Terengganu, Perak and Kedah States (Yeap 2005, McAfee 2017, Kaur et al. 2015, Ong et al. 2009, Yeap and Perumal in press, MNS Hornbill Conservation Project unpub. data). Hybridization between Rhinoceros and Great Hornbills has been reported by Tan (2019) from Panti forests in Johor State. This is a first report for Malaysia, but other similar hybridization occurred in south Thailand reported by Chatmutpong et al. (2013). On Langkawi island, the hornbills have been recorded taking advantage of fruiting strangling fig (Ficus benjamina), congregating in groups of at least 150 individuals (Hasdi Hassan and Siti Hawa Yatim 2003). Yeap et al. (2006) reported casque-butting and bill grabbing behaviour among the hornbills in a smaller group of 30 individuals. Another sizeable group of hornbills was also detected in Belum-Temengor Forest Complex (BTFC) where up to 22 individuals were counted. The group roosted in a Parkia javanica tree for at least 2 nights. This group has been detected at several locations within the Temengor Forest Reserve of BTFC within an area of 32 km² (MNS Hornbill Conservation Project, unpub. data).

Buceros bicornis has a wide distribution, occurring in China (rare resident in west and south-west Yunnan and south-east Tibet), India (locally fairly common, but declining), Nepal (local and uncommon, largely in protected areas), Bhutan (fairly common), Bangladesh (scarce resident in Chittagong Hill Tracts), Myanmar (scarce to locally common resident throughout), Thailand (widespread, generally scarce but locally common), Laos (formerly common; currently widespread but scarce and a major decline has occurred), Viet Nam (rare and declining resident), Cambodia (rare), peninsular Malaysia (uncommon to more or less common) and on Sumatra, Indonesia (now rare). 

The bulk of the population is found in India, where it is restricted to the Himalayan foothills, hill forests in northeast India and, disjunctly, the wet evergreen forests of west India. In the north and northeast there continue to be records from Uttarakhand, Uttar Pradesh, West Bengal, Assam, Meghalaya, Arunachal Pradesh, Nagaland and Mizoram, while in the wet western forests it occurs in Maharashtra, Goa, Karantaka, Kerala and Tamil Nadu (R. Naniwadekar and A. Datta in litt. 2016). Most are found within protected areas, principally National Parks (Rahmani 2012, R. Naniwadekar and A. Datta in litt. 2016), Wildlife Sanctuaries (Birand and Pawar 2004, Rahmani 2012, R. Naniwadekar and A. Datta in litt. 2016), Tiger Reserves (Birand and Pawar 2004, Mudappa and Raman 2009, Rahmani 2012, R. Naniwadekar and A. Datta in litt. 2016), and Reserved Forests (R. Naniwadekar and A. Datta in litt. 2016). The species was not recorded in unprotected forests in a state-wide survey of Arunachal Pradesh, although a significant population does occur in Reserved Forests (Naniwadekar et al. 2015). Outside of protected areas, the species is in severe decline or even locally extinct (Naniwadekar et al. 2015, J. Praveen in litt. 2018). An interview-based survey across Arunachal Pradesh indicated that the species had been lost from five out of 16 sites in recent decades, including from two protected areas (Naniwadekar et al. 2015).

In Nepal, Great Hornbill is present in Royal Chitwan and Bardia National Parks, though at relatively low density. It is patchily common in Bhutan, in the Royal Manas National Park, lower altitudes of the Jigme Singye Wangchuck National Park, southern parts of Phrumshengla National Park, southern parts of Bumdeling Wildlife Sanctuary and Jigme Khesar Strict Nature Reserve, Jomotshangkha and Phibsoo Wildlife Sanctuaries. These areas are the stronghold of the species in Bhutan and populations are apparently stable (Spierenburg 2005).

The Chinese population is restricted to the southwest of the country, with scattered reports in southwest Yunnan along the international borders with Myanmar. It is also common at certain lower elevation forest blocks in Yingjiang County, from where there are breeding records (KFBG, unpubl. data). A mixed flock of 45 Great Hornbills and 102 Wreathed Hornbills were recorded in Ruili City in October 2019, close to the international border with Myanmar’s Kachin State. This species is an occasional visitor to Ruili and the foraging flock probably came from Myanmar (Zheng et al. 2020).
 
In Myanmar it is poorly known, though there are recent records from Sagaing and Kachin states in the north and from Nat Ma Tung National Park in the west of the country (King et al. 2001, eBird 2017).

An assessment of all hornbills across Thailand found Great Hornbill to be one of the more habitat tolerant species, yet the area of occurrence for the species is only approximately one third of the area of suitable habitat present in 1992 (Trisurat et al. 2013). The species has been extirpated from the Mae-Ping-Omkoi protected area complex in north Thailand (Pattanavibool et al. 2004). Away from the north it occurs in most protected-area complexes in the country and is present in particularly high densities in Khao Yai National Park (R. Naniwadekar and A. Datta in litt. 2016).

The species possibly occurred in all hill forests of northeast and southeast Bangladesh only a few decades ago. However, recent records are only from Sangu-Matamuhuri Wildlife Sanctuary and Kassalong Reserve Forest in Chittagong Hill Tracts, SE Bangladesh where patches of old growth forests still exist. The Great Hornbill was recorded three times out of five recent visits (2013-2017) to Sangu-Matamuhuri Wildlife Sanctuary and nearby hills, where there is a resident population (S. U. Chowdhury in litt. 2018).

In Laos the species still present in Nakai-Nam Theun National Biodiversity Conservation Area, but appears to have declined considerably since being historically described as common.

It is now highly localised in Viet Nam, with most recent records from Cat Tien National Park and Deo Nui San in the south, but also from Phong Nha-Ke Bang National Park in central Viet Nam (eBird 2017). 

The Cambodian population is concentrated in southern Mondulkiri in the southeast and the Cardamom and Elephant Mountains in the southwest, with small numbers also present where patches of semi-evergreen  and evergreen forest persist in the north of the country (Goes 2013), and also the northeast of the country in Kratie Province (KFBG, unpubl. data). 

In Peninsular Malaysia it remains widespread. It is present in several protected areas and is common on the island of Langkawi (R. Naniwadekar and A. Datta in litt. 2016, eBird 2017) and Pangkor (Perak) island groups (Yeap 2005, Yeap et al. 2006, Hasdi Hassan and Siti Hawa Yatim 2003, Rahmah Ilias and Hamdon Tak 2009-2010). However, the loss of lowland forest throughout the country is considered to have greatly reduced the area of suitable habitat present. Its stronghold remains in large forest complexes (either single one or several joined) and protected areas (Davison 1995; Lim and Tan 2000; Wells 1999; Chong 1998, 1993; Siti Hawa Yatim 1993; Siti Hawa Yatim et al. 1985; Ong et al. 2000; Choo and Teresa 2001; Norsham and Teresa 2001; Abdul Kadir Abu Hashim 2002; Wells 1999; Yeap & Perumal, in press). In Peninsular Malaysia, most of these have been identified as Important Hornbill Landscapes (IHL), which are also IBAs and linked to the Central Forest Spine Masterplan for Peninsular Malaysia (Yeap and Perumal, in press). In Langkawi, the population is cut off from mainland Peninsular (distance of at least 18 km) but possible to reach Koh Tarutao (Thailand) (about 10 km north of Langkawi Island). It is likely that the Langkawi Great Hornbills ‘travel’ between the islands (possibly to Koh Tarutao as well), tracking fruiting resources. Similarly, in the Pangkor islands Great Hornbills can fly between the forests on the island and mainland, a sea-crossing of about 6-7 km. (Nur Atiqah and Ahmad Tarmizi 2014). The population here however is smaller than that of Langkawi. On Sumatra it is now highly localised and very infrequently seen following extensive destruction of lowland forests (K. D. Bishop in litt. 2012).

Conservation Actions Underway
CITES Appendix I. The species is captively bred in zoos (Jensen 2008). It occurs in several protected areas across its range. The ecology of the species has been studied since 1981 as part of long-running research at Khao Yai National Park in Thailand (Poonswad et al. 1987, Poonswad 1995, Poonswad et al. 1998, 2005). Active management of nesting cavities has been used to augment breeding success in the wild (Poonswad et al. 2005). Hornbill Nest Adoption Programs have been implemented in Budo Sungai-Padi National Park in southern Thailand since 1994 (Pasuwan et al. 2011) and in forests adjoining Pakke Tiger Reserve in Arunachal Pradesh, northeast India since 2011 (Rane and Datta 2015). Urban donors are encouraged to 'adopt' wild hornbill nests and the funds raised are used to pay for nest guardians to monitor and protect the nest sites. An additional nest monitoring and protection program is underway in Kerala with the Kadar community and the forest department (Bachan et al. 2011). Artificial nest boxes have been installed with some success at sites in Thailand (Pasuwan et al. 2011) and southern India (James et al. 2011). In Bhutan, the Great Hornbill is protected under Forest and Nature Conservation Rules and Regulations 2017 (DoFPS, 2017). 

Conservation Actions Proposed
Monitor populations across its range to determine the magnitude of declines and rates of range contraction. Campaign for the protection of remaining extensive tracts of lowland forest throughout its range. Develop a programme to reduce hunting of the species through raising awareness of the status of the species within communities that target the species. Develop the existing captive breeding population to support future reintroduction and supplementation efforts.