With oversized beaks, striking casque structures and distinctive calls, hornbills are among the most recognisable birds of the wet tropics. Yet behind their charismatic appearance lies a growing conservation concern. Many species face mounting pressure from habitat loss, forest fragmentation, hunting and illegal wildlife trade. Several now survive in small, isolated populations across south and southeast Asia, raising concerns about their long-term survival.
A new study by scientists from the CSIR-Centre for Cellular and Molecular Biology (CCMB), Hyderabad and Nature Conservation Foundation (NCF), Mysore, offers insight into how these birds evolved and how their populations have changed over time.
The research team involved Pooja Pawar and Rohit Naniwadekar from NCF, along with Gopi Krishnan and Jahnavi Joshi from CCMB. Using advanced genome sequencing technologies, researchers have decoded the complete genetic makeup of four Asian hornbill species and reconstructed their demographic history over millions of years.
The species examined were the Great Hornbill (Buceros bicornis), Wreathed Hornbill (Rhyticeros undulatus), Rufous-necked Hornbill (Aceros nipalensis) and Malabar Pied Hornbill (Anthracoceros coronatus).
According to the researchers, this represents a significant advance in hornbill biology. Before this work, complete genome information was available for only two of the 32 recognised Asian hornbill species. Genomes are often described as biological archives. By analysing entire genomes, scientists can trace fluctuations in population sizes across thousands and even millions of years. Such information helps reveal how species responded to climatic upheavals, habitat changes and other environmental pressures long before systematic observations became possible.
Ms. Pawar said the study found evidence that all four hornbill species experienced population declines associated with climatic fluctuations during the Pleistocene epoch, which spanned from about 2.58 million years ago to roughly 11,700 years ago. The genomic analyses suggest that repeated cycles of cooling and warming dramatically influenced tropical forests across Asia, affecting habitat availability for forest-dependent hornbills.
Among the four species studied, the Wreathed Hornbill emerged as an exception. Researchers found that it maintained significantly larger population sizes than the other species throughout much of its history. Its peak effective population size was roughly three times that of the Great Hornbill and Rufous-necked Hornbill.
Scientists believe the species may have benefited from its migratory behaviour and broader habitat use. Unlike resident hornbills restricted to pockets of wet evergreen forest, Wreathed Hornbills undertake long-distance seasonal movements and occupy a wider variety of habitats. Large and connected populations generally retain greater genetic diversity, improving resilience and adaptability. The findings align with broader studies showing that migratory bird species often maintain larger long-term populations than non-migratory species.
The researchers also uncovered important clues about hornbill evolution. Comparison with African hornbill lineages revealed substantial expansion in gene families associated with structural keratin, the protein that forms feathers, beaks and claws.
Such evolutionary changes may have contributed to the unique characteristics that distinguish Asian hornbills today, including their prominent casques and other specialised physical features. The study also identified expansion in genes associated with reproductive functions, providing fresh insight into the evolutionary pathways that shaped these unusual birds.
Hornbills are often referred to as “farmers of the forest” because of their ecological role as seed dispersers. Unlike savanna hornbills, which are largely carnivorous, many Asian forest hornbills depend heavily on fruits. By carrying seeds across long distances and depositing them away from parent trees, they play a critical role in forest regeneration. This close association with forests also makes them particularly vulnerable when habitats disappear.
The researchers found that species occupying evergreen forests, such as the Great Hornbill and Rufous-necked Hornbill, were especially sensitive to historical contractions of wet tropical forests. Reductions in forest cover during glacial periods likely contributed to long-term declines and fragmentation. The Malabar Pied Hornbill, which favours moist deciduous forests, displayed a somewhat different demographic pattern but also showed evidence of historical decline.
Three of the four species studied, the Great Hornbill, Wreathed Hornbill and Rufous-necked Hornbill, are listed as ‘Vulnerable’ on the International Union for Conservation of Nature (IUCN) Red List. The Malabar Pied Hornbill is classified as ‘Near Threatened’.
Researchers say the new genomic resources could significantly strengthen conservation planning. Genetic data can reveal levels of allelic diversity within populations, identify isolated groups, measure gene flow and help determine which populations require urgent intervention.
The study also has applications for captive breeding programmes. Previous genetic work found little differentiation among captive Great Hornbills held across several zoos in Thailand, demonstrating the value of genomic information in managing ex-situ conservation efforts.
Samples for the present study were obtained from several locations, including Arunachal Pradesh, the Western Ghats and the Nehru Zoological Park in Hyderabad, enabling comparisons across geographic regions. The researchers have deposited the genome assemblies and sequence data in the National Centre for Biotechnology Information repository, making them available to scientists worldwide. “We believe that this study provides robust genomic resources to support future comparative and conservation genomics efforts for hornbills,” said Mr. Joshi.
Published – July 31, 2026 11:47 pm IST
