Rhinoceros hornbills are found in Southeast Asia. On the Malay Peninsula of the Asian mainland, they inhabit Malaysia, along with southern Thailand and Myanmar. Off the mainland, they inhabit the islands of Borneo, Sumatra, and Java. Rhinoceros hornbills formerly inhabited Singapore but are now extinct on the island. (Chamutpong, et al., 2013; Das and Tuen, 2016)
Rhinoceros hornbills are typically found in primary, lowland rainforests, hill dipterocarp forests, mountainous forests, and swamp forests within elevations of 130 to 1500 meters. Rhinoceros hornbill habitat usually contains large, mature trees and fruit-bearing trees that are required for nesting and feeding. If undisturbed habitat is unavailable, they will inhabit tall secondary forests and slightly disturbed areas. There are reports of Buceros rhinoceros inhabiting smallholdings consisting of palm oil and other crops in Malaysia. However, this is likely a last resort when nearby forests have been disturbed. (Anggraini, et al., 2000; Chaisuriyanun, et al., 2011; Das and Tuen, 2016; Franco and Minggu, 2019; Jambari, et al., 2012; Mansor and Sah, 2012; Misni, et al., 2017)
Rhinoceros hornbills are large forest-dwelling birds. A study on the island of Sumatra found that they typically weigh between 2,180 and 2,580 grams. Another study in Thailand reported females to have an average mass of 2,180 grams. In the great hornbill (Buceros bicornis), the species most closely related to the rhinoceros hornbill, males can be up to 150 centimeters in length, so it likely that male rhinoceros hornbills can also reach this length. Rhinoceros hornbills have black plumage, all black wings, a white vent, and a long white tail with a black band in the center. The bill is large, with a structure called a casque above the upper mandible. The upper and lower mandible are naturally white, but are usually stained an orange-yellow color due to oil secreted from the uropygial gland. The coloration is transferred onto their mandibles and casque during preening. The casque is hollow, curves upwards, and is usually dark orange to reddish in color. There was no mention of geographic or seasonal variation in the literature.
Male and female rhinoceros hornbills look very similar. One distinguishing characteristic is that males have reddish-orange colored irises, while females have bluish-white colored irises. Juveniles look very similar to adults with respect to plumage. Juveniles can be distinguished by an underdeveloped casque and yellow tarsus. Juveniles also have bluish-white irises, no matter the sex. Rhinoceros hornbills that are not yet sexually mature may have lighter or more white mandibles and casque, due to the uropygial gland not producing full color until the bird is completely developed.
Rhinoceros hornbills look very similar to their closest relatives, the great hornbill. One noticeable difference between the two species is that rhinoceros hornbills have completely black wings, while great hornbills have white greater wing coverts. Rhinoceros hornbills have a reddish casque that curves upwards near the tip, while great hornbills have a more yellow casque that is straight. (Chamutpong, et al., 2013; Chan, et al., 2008; Das and Tuen, 2016; Davenport, 2000; Delhey, et al., 2007; Hadiprakarsa and Kinnaird, 2004; Misni, et al., 2017; Poonswad, 2008; Poonswad, et al., 2005)
Rhinoceros hornbills reach sexual maturity at around five years old. The breeding season occurs once a year, between January and June. Females will choose a mate based on the strength of his courtships displays, which often consist of loud calling, duet calling between the male and female, and a head raised posture by the male. Once a mate is chosen, rhinoceros hornbills are likely to remain with their mate for life, as they are monogamous. Behavior before and after copulation is very similar to that of the great hornbill, and may consist of duetting, preening, males offering the female food, billing, and biting. This behavior is believed to strengthen pair bonds. Breeding pairs establish large territories, up to 2.3 square kilometers. Mated pairs are territorial and will defend their home territory if needed. (Anggraini, et al., 2000; Chamutpong, et al., 2013; Das and Tuen, 2016; Kozlowski, et al., 2015; Misni, et al., 2017)
Rhinoceros hornbills breed between January and June, depending on environmental conditions and food availability. The typical clutch size is one to two eggs. Incubation time can range from 37 to 46 days. Once the egg or eggs hatch, the female will remain sealed inside the nest cavity for around 5 to 7 more weeks. The female then will exit the nest but keep the young sealed inside. She helps her mate feed the young until they are fledged, and nearly independent, at about four months old.
Successful hybridization has occurred between rhinoceros hornbills and great hornbills in both captivity and the wild. In the wild, hybridization has been recorded on two separate occasions between a female great hornbill and a male rhinoceros hornbill. Both species eat similar foods, live in similar habitats, have very comparable breeding seasons, and have similar courtship displays, which is why a female great hornbill who cannot find a mate may choose to mate with a male rhinoceros hornbill. Both wild hybridization incidences occurred in Thailand, and each time a hybrid chick was raised successfully by the parents. (Chaisuriyanun, et al., 2011; Chamutpong, et al., 2013; Franco and Minggu, 2019)
Rhinoceros hornbills nest in the hollow cavities of large trees. Being unable to excavate their own cavity into a tree, pairs use pre-existing tree cavities. Rhinoceros hornbill pairs will compete with other rhinoceros hornbills, as well as with other hornbill species, bees, wasps, monitor lizards, giant flying squirrels, and king cobras for nesting cavities within trees. Pairs will attempt to chase away competition, but if the pair becomes too stressed they will abandon the cavity in search of another. The male is tasked with finding a suitable cavity, and the female will nest in it if she approves of it. Females will only nest in cavities that have narrow entrances, often being so small that the she will struggle to enter or exit the cavity. When the female is ready to lay her eggs, she will seal herself inside the cavity. A very narrow cavity entrance allows the pair to spend less time and energy sealing the entrance than if it were a larger opening. However, if the opening is too small for her to fit, the pair may peck around the entrance to make it larger so the female can get inside. The females seal themselves, with the help of their mate, inside the nest using mud, feces, and fruit peels. A small slit is left open to allow the male to poke his bill through, so that he can feed the female and their chick or chicks. While the female is sealed inside, the male is responsible for providing food for the female and their offspring. He may bring the female food up to thirteen times in a single day. He also protects the nest from predators while the female is sealed inside with the offspring. (Chan, et al., 2008; Davenport, 2000; Misni, et al., 2017; Poonswad, 2008; Poonswad, et al., 1999; Poonswad, et al., 2005; Sodhi, et al., 2013)
Rhinoceros hornbills are a long-lived species, living up to 30 years. The great hornbill has been reported living to between 60 and 70 years old, so it is likely that B. rhinoceros can also live this long under the right conditions. (Misni, et al., 2017; Naish, 2015)
Rhinoceros hornbills are diurnal; they are most active in the day and roost at night. During the daytime, they often are most active during the morning and evening. B. rhinoceros are social and noisy birds who communicate through loud vocalizations, such as honking. Breeding pairs are likely to remain in a home territory, and often forage together. Subadults and non-breeding adults often form large flocks that travel long distances together in search of food. In one report, around 70 rhinoceros hornbills were observed flocking together on a palm oil plantation. Pairs are known to be territorial, specifically when fruit trees are ripening. It has been observed that rhinoceros hornbills usually are dominant when in contact with other species of hornbills when feeding on fruits, especially figs. Other, smaller species of hornbills typically wait until rhinoceros hornbills are done feeding and have flown away before attempting to feed from the same fruit tree. There is interspecific competition for nesting cavities during the breeding season, which can lead to less dominant pairs abandoning their nesting location. (Anggraini, et al., 2000; Chan, et al., 2008; Das and Tuen, 2016; Franco and Minggu, 2019; Jambari, et al., 2012; Poonswad, et al., 1999)
Breeding pairs can establish home territories of up to 2.3 square kilometers. (Das and Tuen, 2016)
Rhinoceros hornbills are a social species and primarily communicate through vocalizations. It is believed that the casque may enhance vocalizations by functioning as an acoustic resonating chamber. Their calls are distinctive and very noisy. They can be heard over a large area and are described as a loud honking sound. Vocalizations are an important part of rhinoceros hornbill courtship displays and pair attachment. During courtship and the breeding season, pairs will vocalize together, called duetting. This behavior likely strengthens the pair bond between birds. In great hornbills, males vocalize more frequently during courtship than females do. This behavior likely occurs in rhinoceros hornbills as well. Courtship displays also include a head-raised posture. (Chamutpong, et al., 2013; Chan, et al., 2008; Davenport, 2000; Kozlowski, et al., 2015; Misni, et al., 2017; Naish, 2015)
Rhinoceros hornbills are omnivores, with fruit constituting the majority of their diet. Figs, the fruit of the wild Ficus genus, are their main source of food, with one study finding that figs made up 76.9% of their total diet. Other fruits often eaten include berries from Polyalthia genus, fruit from Parkia speciosa, and fruit from Aglaia spectabilis. They will also eat fruit from Dacryodes rostrat, durians from the Durio genus, and Canarium odontophyllum fruit. For protein, they will also eat invertebrates and small vertebrates. B. rhinoceros will consume invertebrates such as beetles, centipedes, cicadas, worms, grasshoppers, millipedes, scorpions, spiders, and walking sticks bugs. They will also eat fish, small mammals, such as rats and bats, and small reptiles, such as snakes and lizards. (Chaisuriyanun, et al., 2011; Franco and Minggu, 2019; Hadiprakarsa and Kinnaird, 2004; Misni, et al., 2017)
Rhinoceros hornbill eggs and chicks are most susceptible to predation. Predators include the yellow-throated marten (Martes flavigula), the binturong (Arctictis binturong), tree-climbing snakes, and monitor lizards (Varanus sp.). Helmeted hornbills, (Rhinoplax vigil) who are larger than rhinoceros hornbills, will reportedly eat rhinoceros hornbill chicks. A sealed nest cavity helps eggs and chicks remain protected from predators. Humans are also considered predators. Some tribes and villagers hunt rhinoceros hornbills for food. (Davenport, 2000; Hadiprakarsa and Kinnaird, 2004; Poonswad, et al., 1999; Sodhi, et al., 2013)
Rhinoceros hornbills are considered a keystone species and play a very important very role in the rainforest ecosystem, acting as seed dispersers. Studies have shown that rhinoceros hornbills enhance regeneration and maintain the diversity of rainforests. Trees with very large seeds are almost completely reliant on hornbill dispersal, because most other species are not large enough to swallow them. Seeds are transported in their feces, and regurgitated after swallowing fruit.
Within the ecosystem, rhinoceros hornbills can be predators to various species that are often considered pests, such as insects and rats. B. rhinoceros can be a source of prey for various species. Tree-climbing snakes, monitor lizards (Varanus sp), and arboreal mammals such as the yellow-throated marten (Martes flavigula) and the binturong (Arctictis binturong) will eat rhinoceros hornbills. Helmeted hornbills (Rhinoplax vigil) will eat rhinoceros hornbill chicks if given the opportunity. (Chaisuriyanun, et al., 2011; Das and Tuen, 2016; Hadiprakarsa and Kinnaird, 2004; Misni, et al., 2017; Poonswad, et al., 1999; Sodhi, et al., 2013)
The rhinoceros hornbill is a source of food for some villagers and indigenous tribespeople. Their feathers are used in traditional ceremonies, as well as governmental affairs such as banquets or receiving foreign officials. The tail feathers are used in some forms of traditional clothing. People will travel to national and state parks to see rhinoceros hornbills and other hornbill species, helping drive eco-tourism. Hornbills are of interest to scientists, particularly those who are interested in examining how deforestation and logging impact this species. As a source of income, Indonesia and Singapore have exported B. rhinoceros to other countries as pets. (Bennett, et al., 1997; Davenport, 2000; Franco and Minggu, 2019; Nijman and Shepherd, 2015; Sodhi, et al., 2013)
There are no known adverse effects ofon humans.
Rhinoceros hornbills are considered threatened by the IUCN, and populations are declining. Habitat loss, in the form of deforestation, poses the greatest threat to the rhinoceros hornbill. Logging, both legal and illegal, leads to the destruction of nesting sites and food resources. Some villagers and indigenous tribespeople hunt this species for food and feathers. The illegal pet trade is also a threat. Rhinoceros hornbill chicks are captured when they are young, and illegally sold into the international pet trade as a source of income for villagers. Singapore was one of the top exporters of rhinoceros hornbills in the past, and this likely played a role in the extinction of this species from the island. (Bennett, et al., 1997; Nijman and Shepherd, 2015; Sodhi, et al., 2013)
Ashlynn Pryal (author), Northern Michigan University, Alec Lindsay (editor), Northern Michigan University.
uses sound to communicate
young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.
Referring to an animal that lives in trees; tree-climbing.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
uses smells or other chemicals to communicate
helpers provide assistance in raising young that are not their own
to jointly display, usually with sounds in a highly coordinated fashion, at the same time as one other individual of the same species, often a mate
humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
parental care is carried out by females
A substance that provides both nutrients and energy to a living thing.
an animal that mainly eats fruit
An animal that eats mainly plants or parts of plants.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
a species whose presence or absence strongly affects populations of other species in that area such that the extirpation of the keystone species in an area will result in the ultimate extirpation of many more species in that area (Example: sea otter).
parental care is carried out by males
Having one mate at a time.
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
found in the oriental region of the world. In other words, India and southeast Asia.
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
the business of buying and selling animals for people to keep in their homes as pets.
rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.
breeding is confined to a particular season
reproduction that includes combining the genetic contribution of two individuals, a male and a female
uses touch to communicate
Living on the ground.
defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
uses sight to communicate
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