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Bucerotiformes

Bucerotiformes is an order of birds comprising approximately 75 species in three families: Upupidae (hoopoes, 3 species), Phoeniculidae (woodhoopoes and scimitarbills, 8 species), and Bucerotidae (hornbills, including ground-hornbills, 64 species).^[1]^[2] These primarily Old World birds occur across tropical and subtropical regions of Africa, Asia, southern Europe, and parts of the Pacific islands, favoring habitats such as woodlands, savannas, forests, and open grasslands.^[3]^[4] Members of Bucerotiformes exhibit striking morphological adaptations, particularly in their bills, which are specialized for diverse foraging strategies: hoopoes possess slender, decurved bills for probing soil and a prominent erectile crest for display; woodhoopoes and scimitarbills have curved, chisel-like bills ideal for gleaning insects from bark and crevices; and hornbills feature massive, often brightly colored bills topped with hollow casques that may aid in fruit manipulation, vocal resonance, or species recognition.^[5]^[3] Diets vary but commonly include insects, fruits, small vertebrates, and seeds, with many species serving as important seed dispersers in their ecosystems.^[5] Notable behavioral traits define the order, including the hornbills' extraordinary nesting habits, where females of most species (except ground-hornbills) seal themselves into tree cavities with mud and feces during incubation and chick-rearing, emerging only after the young fledge, while males provision through a narrow slit.^[5] Hoopoes are largely solitary or paired but migrate seasonally in some populations, known for their undulating flight and distinctive calls, whereas woodhoopoes are gregarious, traveling in vocal flocks that cooperatively defend territories.^[3] Formerly classified within Coraciiformes, Bucerotiformes was elevated to ordinal status based on molecular phylogenetic evidence supporting its monophyly within the broader Coraciimorphae clade.^[1] Conservation concerns affect several species, particularly larger hornbills vulnerable to deforestation and poaching for bushmeat or trophies.^[6]

Taxonomy and systematics

Classification history

The order Bucerotiformes was first established by Max Fürbringer in 1888 to include the hornbills (Bucerotidae) and hoopoes (Upupidae), based on shared anatomical features of the skeletal and muscular systems derived from his extensive comparative studies of avian morphology. This initial classification recognized the distinctive casque-like bill structures and associated cranial adaptations in these groups as warranting ordinal status separate from other birds.^[7] For much of the 20th century, Bucerotiformes were subsumed within the larger order Coraciiformes, which encompassed roller-like birds including kingfishers, bee-eaters, and rollers, due to superficial similarities in perching habits and aerial foraging behaviors.^[8] This arrangement persisted in major classifications, such as those by Wetmore (1960) and the Sibley-Ahlquist taxonomy (1990), reflecting a reliance on traditional morphological groupings without strong evidence for monophyly. Significant reclassifications emerged in the 1970s and 1990s through detailed morphological analyses, which identified autapomorphic traits distinguishing hornbills and hoopoes from core Coraciiformes, including unique bill casques for nesting and display in hornbills, and zygodactyl foot arrangements in hornbills contrasting with the anisodactyl feet of rollers and kingfishers.^[9] Burton's (1984) anatomical study of the feeding apparatus emphasized syrinx and jaw musculature differences, supporting a sister-group relationship between Upupidae and Bucerotidae while questioning their inclusion in Coraciiformes. Similarly, Mayr (1998, 2006) used osteological data from fossils and extant taxa to argue for the separation of these families, highlighting cranial kinesis and pedal adaptations as key synapomorphies for an independent lineage.^[10] Molecular phylogenetic evidence decisively confirmed the distinctiveness of Bucerotiformes in the 21st century, with Prum et al.'s (2015) genome-wide analysis of 198 bird species placing the order as a monophyletic clade within the landbird assemblage Inopinaves, sister to Coraciiformes and Piciformes. Their divergence-time estimates, calibrated against fossil records, indicate that the Bucerotiformes lineage diverged from Coraciiformes ancestors approximately 50–60 million years ago during the early Eocene, aligning with the post-Cretaceous-Paleogene radiation of neoavians.^[11] The recognition of extinct stem groups has bolstered this framework, with Messelirrisoridae from the middle Eocene of Messel, Germany (ca. 47 million years ago), identified as basal representatives of the hoopoe-woodhoopoe lineage based on preserved osteology and feathering showing primitive upupiform traits. Likewise, Laurillardiidae, known from early Eocene deposits in England, are considered stem Bucerotiformes due to their intermediate coracoid and humerus morphologies linking them to modern hoopoes and hornbills. These fossils underscore an Old World origin for the order during the Paleogene, with subsequent diversification in tropical regions.^[12]

Families and species

The order Bucerotiformes comprises three extant families per the eBird/Clements Checklist v2025: Upupidae, Phoeniculidae, and Bucerotidae (including ground-hornbills). Some classifications, such as those by ITIS and Birds of the World, recognize four families by treating ground-hornbills as a separate family Bucorvidae.^[1]^[13]^[14]^[15]^[16] The family Upupidae includes the hoopoes, represented by a single genus Upupa with three species: the Eurasian hoopoe (Upupa epops), the African hoopoe (Upupa africana), and the Madagascar hoopoe (Upupa marginata).^[13]^[17] The Phoeniculidae, known as woodhoopoes and scimitarbills, encompass two genera: Phoeniculus (five species, including the green woodhoopoe Phoeniculus purpureus and white-headed woodhoopoe Phoeniculus bollei) and Rhinopomastus (three species, such as the common scimitarbill Rhinopomastus cyanomelas).^[14] The family Bucerotidae includes the hornbills and ground-hornbills, with 16 genera and 64 species; ground-hornbills comprise the genus Bucorvus with two species: the northern ground hornbill (Bucorvus abyssinicus) and the southern ground hornbill (Bucorvus leadbeateri). Typical hornbills include genera such as Bycanistes (e.g., white-thighed hornbill Bycanistes leucogaster) and Buceros (e.g., great hornbill Buceros bicornis).^[15]^[18] In total, Bucerotiformes contains 75 extant species across these families.^[1] Phylogenetic analyses indicate early divergence within the order, with the ground-hornbills (Bucorvus) and the Bycanistes clade branching off around 40 million years ago; Phoeniculidae and Upupidae represent distinct early lineages within the order.^[19]^[4] Within Bucerotidae, distinct radiations occurred in Africa and Asia, reflecting biogeographic patterns in the Old World tropics.^[19] Taxonomic debates persist regarding the elevation of certain subspecies to full species status, such as the extinct Saint Helena hoopoe (Upupa antaios), recognized as a distinct species, and the Madagascar hoopoe, which some authorities treat separately from the Eurasian hoopoe based on genetic and morphological differences.^[17] Additionally, generic boundaries within the woodhoopoes (Phoeniculidae) remain under discussion, with potential revisions to the delimitation between Phoeniculus and Rhinopomastus informed by molecular data.^[14]

Physical description

Morphology

Bucerotiformes exhibit a wide range in body size, from approximately 21 cm in length and 28–30 g in weight for the smallest species, the Abyssinian scimitarbill (Rhinopomastus minor), to over 120 cm and up to 6 kg for large hornbills like the southern ground hornbill (Bucorvus leadbeateri).^[20] Hoopoes (Upupidae) are medium-sized at 25–32 cm and 46–89 g, while woodhoopoes (Phoeniculidae) measure 23–46 cm with weights around 50–100 g, and hornbills (Bucerotidae) span 40–120 cm and 100 g to 6 kg.^[21]^[20] The bill is a defining feature, varying by family but adapted for probing and manipulating food. In hornbills, it is large, down-curved, and often topped by a casque—a keratinous, hollow helmet-like structure along the culmen that provides structural support and may aid in vocalization or display, with nostrils positioned at the bill base. Hoopoes have a long, slender, slightly decurved bill suited for soil-probing, while woodhoopoes possess a more strongly decurved, scimitar-like bill for extracting insects from crevices.^[21]^[20] Feet in Bucerotiformes are anisodactyl, with three toes facing forward and one backward. In many species, particularly hornbills and woodhoopoes, the anterior toes exhibit partial syndactyly, facilitating perching, climbing, and balance. This configuration is particularly adapted in ground hornbills for terrestrial walking and foraging on open ground, where the feet support a more upright posture and powerful strides.^[21]^[20]^[22] Wings are generally broad and rounded, enabling agile maneuvers in dense forest environments, especially in arboreal hornbills that rely on short, powerful flights between trees. Tails are long and often graduated in woodhoopoes, providing counterbalance during acrobatic foraging on vertical trunks, while hornbills have moderately long tails for stability in flight.^[20] Skeletal features include large orbital cavities in the skull, supporting prominent eyes for enhanced vision in low-light forest understories, and fused first and second cervical vertebrae (atlas and axis) in hornbills to brace the heavy bill and casque. The digestive system features reduced ceca, an adaptation linked to their predominantly frugivorous diet, which minimizes fermentation needs for fiber processing and prioritizes rapid gut transit for seed dispersal. Sexual dimorphism is most pronounced in hornbills, where males are typically larger overall, with more elaborate and brighter casques compared to females, reflecting potential roles in mate attraction and competition. In hoopoes and woodhoopoes, dimorphism is minimal, with sexes similar in size and structure.^[21]^[20]

Plumage and variation

The plumage of Bucerotiformes is diverse across its families, serving functions in camouflage, display, and thermoregulation, with variations often tied to age, sex, and habitat. Hoopoes exhibit a striking pattern featuring a buff body contrasted by bold black-and-white barring on the wings and tail.^[23] Woodhoopoes display glossy, iridescent plumage that shimmers in metallic hues, while ground hornbills and hornbills tend toward darker, more subdued tones with accents in bare skin or structural features.^[24] These feather types range from soft contour feathers for insulation to stiff remiges for flight, with iridescence arising from structural coloration in barbules.^[25] In hoopoes, the plumage includes a distinctive erectile crest composed of long, black-tipped white feathers that can be raised like a fan, set against a warm buff or cinnamon body coloration. The wings are broadly rounded and black with prominent white bands, creating a barred effect visible during flight, while the tail mirrors this pattern with black feathers edged in white.^[23] This combination provides effective camouflage in grassy habitats when the bird is on the ground but becomes conspicuous in flight.^[26] Woodhoopoes possess glossy blue-black plumage with metallic iridescence that shifts between purple, green, and violet tones depending on light angles, enhancing their social signaling in forest canopies. Adult individuals feature striking red eyes, which contrast sharply with the dark feathers. Juveniles exhibit duller plumage lacking the full iridescence, with shorter, darker bills and feet that gradually develop the adult sheen over the first year.^[24]^[27] Ground hornbills have predominantly black plumage covering the body, providing camouflage in savanna soils, accented by bare red facial skin that inflates during displays. The white primary flight feathers are hidden when perched but become prominently visible in flight, flashing against the dark wings.^[28]^[29] Hornbills show the greatest plumage variation within the order, with bodies ranging from black or sooty brown to gray, often featuring white underparts, throat patches, or wing panels that aid in species recognition. Casques, integrated with the bill structure, are frequently brightly colored in yellow, red, or ivory, varying by species and adding to the visual profile. Eye colors span from yellow and orange to deep red, with some sexual dimorphism in intensity.^[30]^[31] Age and sex variations are evident across Bucerotiformes, particularly in hornbills where juveniles possess smaller, less developed casques and overall duller colors that brighten with maturity. Females in hornbills are often smaller with less vibrant plumage and casque hues compared to males, though sexes are similar in woodhoopoes and ground hornbills. Hoopoe juveniles resemble adults but with softer, less contrasting feather edges.^[32]^[30] Molt patterns in most Bucerotiformes involve an annual complete replacement of feathers post-breeding to maintain insulation and flight efficiency. However, hornbills exhibit a unique adaptation where the female undergoes a rapid, simultaneous molt of her flight feathers (remiges and rectrices) while sealed in the nest during incubation and early chick-rearing, retaining body feathers but temporarily becoming flightless until regrowth completes after fledging.^[33]^[34]

Distribution and habitats

Geographic distribution

Bucerotiformes exhibit a primarily Old World distribution, centered in sub-Saharan Africa where representatives of all families occur, with extensions to southern Europe and temperate Asia via the Upupidae, and to tropical Asia and Melanesia through the Bucerotidae; endemic subspecies are also present in Madagascar.^[15]^[35]^[36] The Upupidae, encompassing hoopoes, possess the widest geographic range within the order, spanning Europe, Asia, North Africa, sub-Saharan Africa, and Madagascar. The Eurasian hoopoe (Upupa epops) breeds across much of this expanse and is partially migratory, with northern populations undertaking seasonal movements to African wintering grounds.^[35]^[37] In contrast, the Phoeniculidae (woodhoopoes and scimitarbills) are strictly endemic to sub-Saharan Africa, distributed widely across savannas and woodlands south of the Sahara.^[14] The Bucerotidae, or hornbills, show a bifurcated distribution between the Afrotropical and Indomalayan realms, with African species such as the southern ground-hornbill (Bucorvus leadbeateri) occurring in savannas from Kenya southward to South Africa, and Asian species like the great hornbill (Buceros bicornis) ranging from India through Southeast Asia to Sumatra and Borneo.^[15]^[38] Migration is limited across the order, with most species sedentary except for certain Upupidae populations.^[37] Fossil records reveal a more extensive historical range, including Eocene representatives in Europe such as Messelirrisor from the Messel Pit in Germany, indicating an early widespread distribution for the clade.^[9] More recently, the Saint Helena hoopoe (Upupa antaios), endemic to the island of Saint Helena, became extinct around the mid-16th century following human arrival.^[39]

Habitat types

Bucerotiformes exhibit a broad spectrum of habitat preferences, spanning open grasslands and savannas to dense tropical rainforests across Africa and Asia. This diversity reflects adaptations to varied ecosystems, with species distributed from sea level to elevations exceeding 3,000 meters. For instance, the Rufous-necked Hornbill (Aceros nipalensis) occurs in montane forests of the eastern Himalayas up to 2,900 meters.^[40] Family-specific habitat requirements highlight ecological niches within the order. Ground-hornbills favor open, dry savannas and sub-desert woodlands in sub-Saharan Africa, tolerating seasonal dryness through behavioral shifts toward riparian and acacia-dominated areas during hot periods.^[18]^[41] Hoopoes (Upupidae) thrive in semi-arid scrub, agricultural fields, grasslands, and open woodlands, preferring areas with bare or lightly vegetated ground suitable for ground-probing foraging and vertical surfaces like cliffs or trees for nesting.^[17]^[42] Woodhoopoes (Phoeniculidae) are adapted to African woodlands, miombo savannas, forest edges, and scrubby areas, often utilizing scattered trees in arid steppes or thornbrush habitats.^[43]^[44] In contrast, hornbills (Bucerotidae) predominantly occupy humid tropical rainforests and woodlands in Asia and Africa, with many species specializing in forest edges and requiring large, mature trees for nesting cavities while avoiding heavily deforested zones.^[15] Microhabitat needs further underscore these preferences. Hornbills depend on proximity to fruiting trees for sustenance, often selecting sites with abundant fig and other canopy resources. Hoopoes require soft, loamy soils in open areas for probing insect prey. African species across families demonstrate tolerance to seasonal aridity, such as through opportunistic use of water sources in dry savannas, while many hornbills exhibit edge-specialist behaviors, exploiting transitional zones between forest and cleared land for enhanced resource access.^[45]^[46]^[47]

Behavior and ecology

Diet and foraging

Members of Bucerotiformes exhibit an omnivorous diet that varies by family, with insects forming the primary component in Upupidae and Phoeniculidae (often over 80% of intake in hoopoes and woodhoopoes), while fruits dominate in Bucerotidae (up to 70% in many hornbill species).^[48]^[14]^[49] Hoopoes primarily consume insect larvae such as cicada nymphs (61% of diet) and beetles, supplemented by arachnids and occasional small reptiles.^[48] Woodhoopoes feed almost exclusively on arthropods, including beetles, ants, termites, and their larvae.^[14] In hornbills, fruits like figs (eaten by all well-studied species) and drupes account for the majority, with insects and small vertebrates such as lizards or nestlings more prominent in ground hornbills.^[49] Foraging strategies reflect these dietary preferences and are adapted to specific microhabitats. Hoopoes probe the ground with their long, decurved bills in bare or sparsely vegetated areas to extract buried prey like larvae.^[48] Woodhoopoes employ acrobatic gleaning techniques on tree trunks and bark crevices, using their curved bills to extract insects, often in coordinated group efforts that include sentinels for vigilance.^[14] Hornbills typically forage in the forest canopy, plucking ripe fruits by sight from branches or in short flights, with some species storing multiple items in a gular pouch before swallowing; ground hornbills, however, hunt on the forest floor for larger prey.^[49] Daily intake in hornbills can include up to 200 small figs or equivalent fruits per feeding bout, supporting their role as key seed dispersers.^[49] Many species shift seasonally toward higher insect consumption during breeding periods to meet protein demands.^[50] Social aspects influence foraging efficiency, particularly in Phoeniculidae, where cooperative group hunting in small flocks enhances detection and access to hidden arthropods, while most Bucerotidae forage solitarily or in pairs.^[14] Digestive adaptations in fruit-dependent hornbills facilitate seed dispersal: they lack a gizzard and possess a rapid gut transit that digests only the pulp, regurgitating large seeds intact after retention times of 1-13 hours, often enhancing germination.^[49]

Reproduction

Breeding in Bucerotiformes is typically seasonal and synchronized with the onset of the rainy season in tropical regions, often spanning March to July in parts of Africa and Asia, though timings vary by family and location to align with peak food availability such as insect abundance or fruiting events.^[51]^[52] Most species form monogamous pairs that maintain strong bonds across breeding seasons, with biparental care common post-fledging; cooperative breeding involving non-breeding helpers occurs in woodhoopoes (Phoeniculidae) and ground-hornbills (Bucerotidae), where retained offspring assist in provisioning.^[53] Nesting strategies differ markedly among families but emphasize cavity use for protection. Hornbills (Bucerotidae) exhibit a distinctive behavior where the female enters a natural tree cavity before egg-laying and seals the entrance with a wall of mud, fruit pulp, and her own feces mixed with frass, leaving only a narrow vertical slit for the male to deliver regurgitated food boluses.^[51]^[15] This self-imprisonment lasts through incubation and much of the nestling period, during which the female undergoes a complete molt and remains entirely dependent on the male; she breaks out once the chicks are large enough to maintain the seal themselves. In contrast, hoopoes (Upupidae) and woodhoopoes nest in existing tree cavities, rock crevices, or occasionally abandoned woodpecker holes without sealing the entrance, relying on the site's natural concealment and adding minimal lining such as feathers or debris.^[52] Ground-hornbills use large tree cavities, rock ledges, or termite mound chambers, also without sealing, and often reuse the same site over multiple years with group members helping to prepare it by adding dry leaves or soil.^[53]^[54] Clutch sizes range from 1 to 12 eggs across the order, laid at intervals of 1–3 days, with species-specific averages: typically 2–4 for hornbills and woodhoopoes, 4–7 for hoopoes, and 1–3 (usually 2) for ground-hornbills, where asynchronous hatching often results in only one chick surviving due to siblicide or starvation.^[51]^[52]^[53] Eggs are white and unmarked in most species. Incubation is performed solely by the female and lasts 15–18 days in hoopoes, 25–40 days in hornbills, and about 37–41 days in ground-hornbills, with the male provisioning the female through the nest slit in hornbills or directly in other families.^[51]^[52]^[55] Nestling periods extend 26–29 days in hoopoes, 45–90 days in hornbills (with chicks using their wide gapes to receive food through the slot), and up to 80 days in ground-hornbills, after which fledglings remain dependent on parents or group helpers for several months to years.^[51]^[56] Biparental care dominates post-fledging, supplemented by helpers in cooperative species that deliver food and defend the brood, enhancing survival in resource-variable environments.^[54] Bucerotiformes display diverse social systems, ranging from monogamous pairs to cooperative groups. Most hornbill species (Bucerotidae) maintain solitary territorial pairs throughout the year, with occasional facultative cooperation involving offspring as helpers during breeding seasons.^[57] In contrast, woodhoopoes and scimitarbills (Phoeniculidae) form stable family groups or clans of up to 12 individuals, consisting of a breeding pair and retained offspring that assist in rearing subsequent broods.^[58] Ground hornbills (Bucerotidae) live in small, cohesive groups of 2–8 members that defend large territories together, exhibiting strong social bonds through shared activities like roosting and foraging.^[59] Communication within Bucerotiformes relies heavily on vocalizations and visual displays to maintain group cohesion and deter rivals. Hornbills produce hoarse, barking calls such as the "wok-wok" of species like the African grey hornbill, used for contact and alarm signaling.^[58] Hoopoes (Upupidae) emit trilling, hoo-poo-poo songs that serve as territorial announcements and pair coordination.^[60] Visual signals include crest-raising in hoopoes to signal agitation and casque-banging in some hornbills, where males rhythmically tap their casque against branches to attract mates or advertise territory.^[61] Territoriality is a core aspect of social organization in the order, with year-round defense common across families. Pairs or groups of hornbills engage in coordinated duets to proclaim boundaries, while ground hornbills use deep booming calls—resonant four-note sequences audible up to 5 km away—to assert dominance over vast ranges of 50–200 km².^[28]^[62] These vocal displays reinforce monogamous pair bonds and prevent intrusions, with groups often responding chorally to amplify their presence.^[59] Cooperative breeding occurs in approximately 20% of Bucerotiformes species, particularly in woodhoopoes and some hornbills, where non-breeding helpers—typically previous offspring—contribute to chick provisioning and nest defense.^[61] Helpers perform allopreening to maintain plumage hygiene within the group and act as sentinels, alerting members to predators during foraging.^[63] This system enhances fledging success in resource-scarce environments, though it is often facultative, with pairs breeding independently when helpers are absent.^[57] Interspecific interactions highlight the order's ecological integration, including mutualisms that benefit Bucerotiformes. Ground hornbills form foraging partnerships with dwarf mongooses (Helogale parvula), where hornbills provide aerial vigilance against raptors in exchange for access to insects flushed by the mammals.^[64] Additionally, many hornbill species act as key seed dispersers, consuming fruits and depositing seeds away from parent plants via defecation, fostering plant regeneration in tropical forests.^[58]

Conservation

Status and threats

The conservation status of Bucerotiformes varies across its families, with hornbills facing the greatest risks while most hoopoes and woodhoopoes remain secure. According to assessments by BirdLife International for the IUCN Red List, 26 of the 62 hornbill species (about 42%) are classified as threatened or near threatened with extinction as of 2025; in contrast, the 3 hoopoe species and 8 woodhoopoe and scimitarbill species are predominantly Least Concern, with no threatened species in those families.^[65] For example, the great hornbill (Buceros bicornis) is listed as Vulnerable due to ongoing habitat loss and hunting, while the southern ground hornbill (Bucorvus leadbeateri) is also Vulnerable, primarily from habitat degradation and persecution. The primary anthropogenic threats to Bucerotiformes include habitat fragmentation and deforestation, which drive the majority of population declines in Asian hornbills by reducing large tracts of old-growth forest essential for nesting and foraging. Hunting for meat, feathers, and traditional medicine poses severe risks to African hornbill species, often exacerbating habitat pressures through bushmeat trade.^[66] Nest poaching for the pet trade and chicks further threatens breeding success across the order, particularly for cavity-nesting hornbills.^[67] Regionally, the bushmeat trade in Africa has led to significant declines in forest hornbills, with international demand amplifying local hunting.^[66] In Southeast Asia, logging operations diminish fruit availability by targeting fig and other key food trees, disrupting the seed-dispersal role of hornbills. Climate change is beginning to alter migration patterns for hoopoes in open habitats, potentially affecting breeding success through shifted phenology of insect prey.^[17] Population trends indicate declines of 30-50% over the last three generations for many forest-dependent hornbills, driven by cumulative habitat loss and exploitation. In contrast, populations of open-habitat hoopoes, such as the common hoopoe (Upupa epops), remain stable due to their adaptability to agricultural landscapes.^[17] One notable extinction in the order is the Saint Helena hoopoe (Upupa antaios), which disappeared in the mid-19th century owing to habitat clearance and introduced predators.

Conservation measures

Conservation efforts for Bucerotiformes emphasize the establishment and expansion of protected areas to safeguard critical habitats for hornbills, hoopoes, and woodhoopoes. In Africa, the Dja Biosphere Reserve in Cameroon serves as a vital stronghold, encompassing over 500,000 hectares of lowland rainforest that supports populations of several African hornbill species, including the black-and-white casqued hornbill (Bycanistes subcylindricus). In Asia, Kerinci Seblat National Park in Sumatra, Indonesia, one of the largest protected areas in Southeast Asia at approximately 13,791 square kilometers, harbors diverse hornbill species such as the rhinoceros hornbill (Buceros rhinoceros) and contributes significantly to conserving hornbills through its intact tropical forests.^[68] These sites, along with others like national parks in India and Thailand, form a network that protects hornbill habitats from deforestation and encroachment.^[69] Legal frameworks provide essential protections against trade and hunting. Under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), 29 hornbill species are listed in Appendix I or II, prohibiting or regulating international trade to prevent overexploitation; for instance, the helmeted hornbill (Rhinoplax vigil) is in Appendix I due to intense poaching for its casque.^[70] Nationally, India enforces bans on hornbill hunting through the Wildlife Protection Act of 1972, while Indonesia's Law No. 5/1990 on Conservation of Living Resources prohibits the capture and trade of protected hornbills, with penalties including fines and imprisonment.^[71] These measures have helped curb illegal trade, though enforcement remains challenging in remote areas. At the CITES CoP20 (24 November - 5 December 2025), proposals are under consideration to list additional African hornbill species in Appendix II to regulate international trade.^[72] Community-based initiatives foster local stewardship and reduce human-wildlife conflict. In India, annual hornbill festivals, such as the Pakke Paga Hornbill Festival in Arunachal Pradesh and the Hornbill Festival in Nagaland, raise awareness about conservation, engaging indigenous communities like the Nyishi and Naga tribes to promote anti-poaching and habitat protection, transforming former hunters into advocates.^[73] In Thailand, the Thai Hornbill Project employs locals, including former poachers, in nest-guarding programs that monitor and protect breeding sites, reducing poaching incidents by up to 80% in monitored areas and safeguarding approximately two-thirds of broods from exploitation.^[74] Research and monitoring efforts guide targeted interventions. The IUCN Species Survival Commission Hornbill Specialist Group coordinates global assessments, developing conservation action plans for all Endangered and Vulnerable hornbill species by the end of 2025, including population surveys using camera traps to track declines and habitat use in regions like Borneo and West Africa. Reintroduction trials for the Southern ground hornbill (Bucorvus leadbeateri), a Vulnerable species, have been ongoing since 1995 through projects like the Mabula Ground Hornbill Project in South Africa, which releases captive-raised juveniles into suitable habitats to bolster wild populations, with monitoring showing initial survival rates of released groups.^[75] Notable successes demonstrate the efficacy of integrated approaches. Habitat restoration in European farmlands has led to population recovery in subspecies of the Eurasian hoopoe (Upupa epops), such as through grazing management that creates short-grass foraging areas, enabling recolonization in restored reserves.^[76] Ex-situ breeding programs have advanced conservation for endangered hornbills; for example, the Katala Foundation in the Philippines achieved the first captive breeding of the Vulnerable Palawan hornbill (Anthracoceros marchei) in 2025, producing viable offspring for potential reintroduction, while species survival plans in zoos support genetic diversity for species like the rhinoceros hornbill (Buceros rhinoceros).^[77]^[74]

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[16]
Bucerotidae - Hornbills - Birds of the World
Oct 28, 2025 · Mayr (2006). Diversification of Neoaves: integration of molecular ... Bucerotiformes from it. The ground-hornbills (Bucorvus) are ...
[17]
Common Hoopoe Upupa Epops Species Factsheet
The overall population is estimated at 5,000,000-10,000,000 individuals (Krištín and Kirwan 2015). The European population is estimated at 1,300,000-2,760,000 ...Missing: count | Show results with:count
[18]
A comprehensive molecular phylogeny for the hornbills (Aves
We present the first complete phylogeny for all 61 hornbill species based on nuclear and mtDNA sequences.
[19]
https://www.sciencedirect.com/science/article/abs/pii/S1055790313000699
[20]
https://doi.org/10.2173/bow.phoeni2.01
[21]
Plumages, Molts, and Structure - Common Hoopoe - Upupa epops
Oct 22, 2024 · Remainder of head, nape, upper back feathers, and marginal upperwing lesser coverts are variably buff-orange, cinnamon, and/or grayish tan, ...
[22]
Green Woodhoopoe - Phoeniculus purpureus - Birds of the World
Close ). Juvenile without iridescence, and has short dark bill and dark feet; most juvenile males and some females have brown or buff throat ; tail spots ...
[23]
Green Woodhoopoe - Coraciiformes Tag
Groups are often seen following each other from tree to tree while foraging in cracks and crevices. During the dry season they also forage on the ground.Missing: balance | Show results with:balance
[24]
Hoopoe - BTO
Unmistakable, with its down-curved bill, black, white and sandy brown plumage – not to mention its crest – this is a striking visitor to our shores, ...
[25]
Green Woodhoopoe - Indianapolis Zoo
These colorful birds are known for their deep green, blue and purple feathers, magnificent red beak and loud chattering call—kuk-uk-uk-uk!Missing: plumage variation
[26]
Southern Ground-Hornbill - SANBI
Jul 24, 2018 · Adult birds generally have black plumage, which covers the entire body, except 10 primary feathers and their coverts, which are usually white.
[27]
Southern Ground Hornbill (Bucorvus leadbeateri) Fact Sheet
Oct 17, 2025 · Shared hornbill features (from Kemp and Crowe 1985). Skeletal characteristics. Cervical vertebrae. Axis and atlas are fused. Casque on top of ...
[28]
Hornbill - San Diego Zoo Animals & Plants
Hornbills have a large, curved bill, a casque, long tail, broad wings, and varied colors. They have a special body part atop their bill called a casque.Missing: rounded | Show results with:rounded
[29]
Plumages, Molts, and Structure - Rufous Hornbill - Buceros hydrocorax
Sep 17, 2021 · Northern populations usually have deep red irides, although occasionally they are pale blue; and in southern populations, the eyes are always ...
[30]
Western Red-billed Hornbill Tockus kempi - Birds of the World
Jan 17, 2025 · Sexes are similar in plumage but in both Females and Males (separable by bill pattern), the can remain duller and duskier red than in adults of ...
[31]
Plumages, Molts, and Structure - Malabar Gray Hornbill
Mar 17, 2023 · The Preformative Molt appears to include most head feathers and a variable number of scattered other body feathers but no upperwing coverts, ...
[32]
The simultaneous moult of female hornbills is not triggered by the ...
Aug 6, 2025 · Most females underwent a simultaneous moult of their remiges and retrices following clutch completion, regardless of the amount of time they had ...
[33]
Distribution - Common Hoopoe - Upupa epops - Birds of the World
Oct 22, 2024 · In Europe, the Common Hoopoe breeds north to France (except northwestern strip), southern and eastern Germany, Latvia, the Moscow of area of ...
[34]
Bucerotiformes – Hornbills & Hoopoes: facts, distribution & population
Bucerotiformes is an order of birds including hornbills, hoopoes, and woodhoopoes, found in Africa, Asia, and Melanesia, with unique characteristics.
[35]
Movements and Migration - Common Hoopoe - Upupa epops
Oct 22, 2024 · Southbound migration involved a median of 115 h of flying time to cover a median distance of 3,769 km, while northbound migration involved 117 h ...Dispersal and Site Fidelity · Migration Overview · Timing and Routes of Migration
[36]
Southern Ground-Hornbill Bucorvus leadbeateri - Birds of the World
Oct 28, 2025 · Southern Kenya, and Rwanda south to southeastern Democratic Republic of the Congo, Angola, northern Namibia, northern and eastern Botswana, and ...
[37]
Upupa antaios (St. Helena Hoopoe) - Avibase
The Saint Helena hoopoe, also known as the Saint Helena giant hoopoe or giant hoopoe, is an extinct species of the hoopoe, known exclusively from an ...
[38]
Rufous-necked Hornbill Aceros Nipalensis Species Factsheet
Occasional elevation limits. 150 - 2,900 m. Generation length. 9.4 years. Species type. Landbird. Habitat classification. Habitat (level 1). Habitat (level 2) ...<|control11|><|separator|>
[39]
(PDF) Seasonal changes in movement and habitat use by Southern ...
Southern Ground-Hornbills show seasonal habitat selectivity, favoring acacia and riparian habitats during the hottest periods, particularly in Early and Late ...Missing: dryness | Show results with:dryness
[40]
Upupidae – The Hoopoe Family, their Habitats and Distribution
Aug 6, 2020 · Hoopoes need bare ground for foraging and vertical surfaces such as trees and cliffs for nesting. They occur in a wide range of habitats such as ...
[41]
Woodhoopoes (Phoeniculidae) - Encyclopedia.com
Medium-sized to small birds with long, slender, decurved bill; plumage mainly black, with green or purple gloss; broad, rounded wings and long, graduated tail.Missing: body | Show results with:body
[42]
Woodhoopoe (Phoeniculidae); Hoopoe (Upupidae) - The World Birds
It has a long white-marked tail, a long curved red bill, and red legs. The similar black-billed woodhoopoe has a black bill. The green woodhoopoe is up to 40 ...Missing: morphology anatomy body
[43]
[PDF] Hornbill Natural History and Conservation
Borneo, the third-largest island in the world, is home to eight species of hornbills: White- crowned Hornbill (Berenicornis comatus), Wrin- kled Hornbill ( ...
[44]
[PDF] Diet and foraging ecology of the Hoopoe Upupa epops in a ...
Habitat selection analysis indicates that short herbaceous sward and low herbaceous cover are the fundamental factors driving foraging microhabitat selection.
[45]
Hornbill abundance and habitat relationships in a human-impacted ...
The altitude ranges from 65–1750 m above sea level. Many perennial rivers and streams flow through the reserve. The reserve has immense ecological and ...
[46]
(PDF) Diet and foraging ecology of the Hoopoe Upupa epops in a ...
The Eurasian Hoopoe Upupa epops adopts a diverse diet consisting of insects, arachnids, annelids, crustaceans, reptiles and more (Annessi et al. 2022) . In ...
[47]
Frugivory and seed dispersal by hornbills (Bucerotidae) in tropical forests
### Hornbills Diet Composition, Foraging Methods, Seed Handling, and Quantitative Data
[48]
Diet selection is related to breeding status in two frugivorous hornbill ...
Jun 23, 2014 · Here, we quantify annual patterns of fruit availability and diet for two frugivorous hornbill (Bucerotidae) species over a 5.5-y period to test ...
[49]
[PDF] reproduc - Hornbill Specialist Group
morphological variation within allopatric populations of each of the two subspecies we have considered. Moreover, the two subspecies considered here exhibit ...
[50]
Breeding - Common Hoopoe - Upupa epops - Birds of the World
Oct 22, 2024 · The size of a full clutch varies from 2–12 eggs, and the mean clutch size ranges from 5.3–7.04 eggs, but these number vary greatly by location.
[51]
Southern Ground-hornbill Bucorvus Leadbeateri Species Factsheet
2016), mainly from September to December, with a clutch of 1-3 (usually 2) eggs, although only one survives to fledging (del Hoyo et al. 2001, Chiweshe, L. Kemp ...
[52]
Breeding biology of Southern Ground Hornbill Bucorvus leadbeateri ...
Summary. This paper summarizes current knowledge and outlines future work on the breeding biology of Southern Ground Hornbill Bucorvus leadbeateri in ...<|control11|><|separator|>
[53]
Abyssinian ground hornbill - National Zoo
An Abyssinian hornbill's most obvious identifying feature is its large beak, topped with a bony prominence called a casque. However, they also boast striking ...Missing: plumage | Show results with:plumage
[54]
Eurasian hoopoe - Wikipedia
... downcurved bill. Its call is a soft "oop-oop-oop". Eurasian hoopoe ... The muscles of the head allow the hoopoe's bill to be opened when it is inserted into the ...Missing: straight | Show results with:straight
[55]
Reproduction & Development - Southern Ground Hornbill (Bucorvus ...
Oct 17, 2025 · Juveniles and subadults remain with their parents for several years. Though individuals are capable of feeding themselves by 6 months of age, a 2 year old may ...Missing: biology | Show results with:biology
[56]
[PDF] EAZA Hornbill Management and Husbandry Guidelines
The guidelines cover captive population management, veterinary care, environmental conditions, diet, reproduction, and social behavior of hornbills.
[57]
Bibliography: African Hornbills |
... genera, 70 families, and 25 orders. The orders most represented were Passeriformes (107 species), Falconiformes (45 species), and Coraciiformes (24 species) ...
[58]
Behavior & Ecology - Southern Ground Hornbill (Bucorvus ...
Oct 17, 2025 · Become active near dawn. Group members produce deep, booming territorial calls (see description of vocalization below); Fly down from trees ...
[59]
https://ielc.libguides.com/sdzg/factsheets/southern_groundhornbill/behavior
[60]
Environmental stability and the evolution of cooperative breeding in ...
Aug 6, 2025 · Ancestral state reconstruction of social system in hornbills using stochastic character mapping. Black squares and branches indicate cooperative ...
[61]
From a distance the iconic deep booming calls of a ground-hornbill ...
May 13, 2022 · These low frequency calls travel incredibly far on a still, crisp morning in the bush. With their territories being very large (50-200 square km) ...
[62]
Allopreening in birds is associated with parental cooperation over ...
Jun 9, 2017 · We found that allopreening between breeding partners was more common among species where parents cooperate to rear offspring.
[63]
Dwarf mongoose and hornbill mutualism in the Taru desert, Kenya
Dwarf mongooses in the Taru desert region of Kenya form foraging communities with a variety of endemic bird species, especially hornbills, and are exposed ...Missing: seed dispersal<|control11|><|separator|>
[64]
IUCN SSC Hornbill Specialist Group
There are 62 hornbill species in the world—32 in Asia and 30 in Africa. Currently, 26 of them are Globally Threatened or Near Threatened with extinction, ...
[65]
Intense international exploitation of African hornbills necessitates ...
... BirdLife International ... Every hornbill species is potentially threatened by intensifying international trade, if it remains unregulated.<|control11|><|separator|>
[66]
[PDF] Hornbill Natural History and Conservation
Furthermore, four other species were up-listed by one threatened status in 2018: Rhinoceros Hornbill. Buceros rhinoceros, Great Hornbill Buceros bicor- nis, and ...
[67]
Kerinci-Seblat National Park - ASEAN Centre for Biodiversity
Kerinci-Seblat National Park is one of Southeast Asia's largest conservation areas. It harbours the oldest tropical rainforest in Asia and protects the world's ...
[68]
[PDF] Hornbill Natural History and Conservation
Nevertheless, areas outside protected areas can offer potentially suitable habitats for some hornbill species. Thus, increasing connectivity of suitable ...<|control11|><|separator|>
[69]
[PDF] CoP17 Doc. 69 - CITES
A draft Action Plan for the Conservation of Helmeted Hornbill ... protect this species, including relevant conservation actions, legal and regulatory measures,.
[70]
[PDF] SC69 Doc. 61 (Rev. 1) - CITES
– In Peninsular Malaysia, hornbill species are protected under the Wildlife Conservation Act of 2010. – In Sabah (Malaysia), the helmeted hornbill is ...
[71]
Pakke Paga Hornbill Festival begins in Arunachal - Down To Earth
Jan 18, 2024 · Pakke Paga Hornbill Festival begins in Arunachal; effective conservation of iconic birds urged ... The three-day festival will end on January 20.
[72]
[PDF] 2021 – 2023 Asian Hornbill SAFE Program Plan
Jun 22, 2021 · The Asian Hornbill SAFE Program aims to support the sustainability of wild Asian Hornbills through conservation planning and actions, and to ...
[73]
(PDF) Review of trial reintroductions of the long-lived, cooperative ...
Reintroductions of the Southern Ground-hornbill Bucorvus leadbeateri have been tested as a potential conservation tool for this vulnerable species since 1995.
[74]
The hoopoe is back. This year, scientists watched the species for the ...
Sep 25, 2018 · Hoopoes returned to the reserve due to grazing creating short-grass areas, and the presence of large herbivores, which provide food in their ...
[75]
Palawan Hornbill finds new hope after first successful breeding in ...
Nov 2, 2025 · For the first time, Katala Foundation, Inc. (KFI) has successfully bred the Palawan hornbill (Anthracoceros marchei) in captivity, a ...