Both Phayre’s langurs and capped langurs are at risk of extinction worldwide. In Bangladesh, these two species inhabit the forests of the Sylhet and Chattogram regions. Due to the loss of habitat and myriad anthropocentric pressures, their populations are declining. Recent research by Bangladeshi and German scientists has revealed shocking findings: hybrids between these two species of langurs.
Researchers state that the reduction of forest area in Sylhet is leading to interbreeding between the two distinct species of langurs, resulting in the birth of hybrid langurs. This trend poses a threat to the long-term survival of these species and raises concerns about the extinction risks.
Conducted from June 2017 to October 2023, the study involved field research by a team of 12 Bangladeshi researchers under the supervision of two famous German primatologists– Professor Dr. Christian Roos and Dr. Dietmar Zinner. The team leader, Tanvir Ahmed, a former student of Jagannath University in Dhaka and a PhD researcher at the University of Göttingen and the German Primate Center in Germany, recently published their findings in the International Journal of Primatology.
The study identifies mixed-species groups and confirms hybridization between the endangered Phayre’s langurs (Trachypithecus phayrei) and capped langurs (Trachypithecus pileatus).
In addition to the researchers from the German Primate Center, the team included Professor Dr. Sabir Bin Muzaffar from a United Arab Emirates University and lead researcher Md. Sabit Hasan from the Isabela Foundation, and several students, local eco-guides, and wildlife photographers. The research was conducted with permission from the Bangladesh Forest Department.
To confirm the hybrid status, genetic tests were conducted on langur feces in German laboratories. Phayre’s langur is classified as a globally Endangered species and Critically Endangered in Bangladesh by the IUCN Red List of Threatened Species. Their range is limited to Bangladesh, India, and the Irrawaddy River in Myanmar.
On the other hand, capped langurs are listed as vulnerable globally and endangered in Bangladesh. They are also found in India, Bhutan, Myanmar, and small areas of China. In Bangladesh, these two langur species reside in various hilly forests of Sylhet and Chittagong divisions, as well as in Madhupur’s deciduous forests. However, there is limited data on the current populations of these two species globally.
Typically, groups of Phayre’s langurs consist of 4 to 26 individuals, while capped langur groups range from 4 to 17. Both species are primarily arboreal but also move on the ground when necessary. Their diet consists mainly of wild leaves, flowers, fruits, and insects, playing a vital role in dispersing seeds throughout the forest, which helps rejuvenate the ecosystem.
Research Background
Tanvir Ahmed, team leader of the research, said, “In 1997-98, during his PhD research in Rema-Kalenga, Professor Dr. Mofizul Kabir from Jahangirnagar University first observed two temporary mixed-species groups of Phayre’s and capped langurs. No hybrids were present. Nearly 20 years later, in 2017, we were astonished to see a possible hybrid langur in Satchari National Park.”
During the first phase of field research, the team surveyed langurs in the protected areas of Lawachara, Satchari, Rema-Kalenga, Rajkandi, Patharia, and Atora forests in Sylhet Division over 92 days. For nearly four years, they monitored mixed-species groups. They observed a total of 98 langur groups: 41 Phayre’s langur groups, 49 capped langur groups, and 8 mixed-species groups.
Ahmed and the team members identified three potential hybrids based on physical characteristics in three mixed groups, two in Satchari National Park and one in Rema-Kalenga Wildlife Sanctuary. One of the hybrids was a mature female, showing signs of motherhood, while the other two were juveniles. To confirm hybridization, genetic tests were performed on fecal samples collected from Satchari National Park.
The study revealed groundbreaking information, indicating that a hybrid langur born in Satchari in 2023 had a Phayre’s langur father and a capped langur mother. Ahmed added, “The presence of hybrid langurs is particularly alarming, as it suggests that genetic flow between these two endangered species could have irreversible effects on their future genetic structure.”
A Rare and Natural Event
Researchers emphasize that hybridization is a rare but natural occurrence, generally happening where the ranges of two species overlap. This phenomenon has been observed in many animal species and is a crucial topic in discussions about evolution and taxonomy. However, human activities such as deforestation, habitat fragmentation, illegal hunting, and trade are increasing the risks of hybridization among primates. Recently, this trend has been observed in several langur species across Asia.
Professor Dr. Christian Roos from the German Primate Center said, “This is not just a local problem—it’s part of a broader, global challenge. When habitats are destroyed, animals mix unnaturally, leading to hybridization, which can push one or both species toward extinction.”
The research also indicated that langur densities are significantly higher in well-protected areas like Lawachhara and Satchari National Parks and Rema-Kalenga Wildlife Sanctuary compared to Rajkandi, Patheria, and Atora. However, these protected forests are often small and isolated, limiting genetic exchange among populations. Therefore, researchers have called for stronger forest conservation policies in Bangladesh.
During the survey, approximately 500 spectacled langurs and 600 black-faced langurs were observed in the Sylhet region. Researchers attribute the increasing habitat destruction to human activities such as land encroachment for housing, agriculture, illegal logging, and uncontrolled tourism. Additionally, illegal hunting, electrocution, and vehicular collisions are further contributing to the decline in langur populations. Consequently, the researchers advocate for urgent conservation initiatives, including forest protection and the establishment of wildlife corridors.
Tanvir Ahmed stressed, “Forest conservation must be a national priority. If we don’t take action now to protect these habitats, we risk losing not just two species of langurs but also a crucial part of Bangladesh’s biodiversity.”
Co-researcher Dr. Dietmar Zinner emphasized the importance of ongoing monitoring of the remaining langurs and in-depth studies on hybrids to understand the genetic impacts of hybridization and to develop effective conservation strategies. He concluded, “The results of this research serve as a wake-up call; this is just the beginning. We need more data to create long-term conservation strategies. Further research is essential to understand the extent of hybridization, its relationship with human activities, and how to mitigate its most severe effects.”
