Study decodes hornbill genomes to aid conservation in Asia

Hornbills, with their oversized beaks and striking casque structures, are among the most recognisable birds of Asia's wet tropics. Yet 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 valuable insight into how these birds evolved and how their populations have changed over time. The research team, including Pooja Pawar and Rohit Naniwadekar from NCF, along with Gopi Krishnan and Jahnavi Joshi from CCMB, used advanced genome sequencing technologies to decode the complete genetic makeup of four Asian hornbill species and reconstruct 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 in new areas, they help forests regenerate. Understanding their genetic history is crucial for designing effective conservation strategies, especially for species living in fragmented habitats where genetic diversity may be eroding.

The study underscores the importance of genomic research in conservation science. It provides a baseline for monitoring genetic health in hornbill populations and could help identify populations most at risk from future environmental changes. As Asia's forests face increasing pressure, such scientific insights are essential for ensuring that these iconic birds—and the ecosystems they support—survive for generations to come.