While our three-wheeler ride moved through the countryside of north-east Bangladesh, I looked at the plains where people were out in their fields—ploughing, irrigating or simply standing with their hands clasped behind their back. The road we took that winter morning in 2017 ran through seasonal freshwater wetlands and farmlands. From dawn to dusk we were travelling from one village to another, one wetland to another, looking for the globally threatened Pallas’s fish eagle Haliaeetus leucoryphus, which for hundreds of years has visited this rich land to build nests and produce offspring.

An adult Pallas’s fish eagle with prey. Photo: Sayam U. Chowdhury

In 2017, the species was recategorized from Vulnerable to Endangered on the IUCN Red List. The latest evidence shows that globally there is only a single migratory population, which breeds in the Indian subcontinent in winter (October–April) and migrates north of the Himalayas in the summer (May–September). This population is rapidly declining as a result of continuing, widespread loss and degradation of freshwater wetlands. We wanted to identify all nests in north-east Bangladesh, study the species’ nesting ecology, identify key threats and work towards mitigation.

Graphical abstract of a Pallas’s fish eagle nest site and habitat characteristics, with distances wetland, human activity, houses, road and river. Photo: Bangladesh Raptor Research and Conservation Initiative.

We first conducted a pilot study in an area known to contain a high density of Pallas’s eagle nests. We tested various survey methods to detect the eagle nests, so we could identify the most suitable method for our study, supported by the Oriental Bird Club. As we began to talk to villagers, we quickly realized that most people near a Pallas’s fish eagle nest were aware of the species’ presence, primarily because of its large size, very loud breeding calls, and long associations with the traditions, culture and religion of local communities. During our interviews a village elder named Hason Ali shared a fascinating story about the eagle: “when technology didn’t reach this land, the unique call of the eagles used to tell us about the hours after dark and woke up people who wanted to pray past midnight […] the eagle was attuned to our biological clock”.

Left: Local people and researchers observing a Pallas’s Fish Eagle nest during the interview survey. Photo: Nazim Uddin Khan. Right: Pallas’s Fish-eagle nest protection workshop at Sunamganj in north-east Bangladesh, November 2020. Photo: Syed S. Inam

We carried out interviews at various distances from nests, and found that 95% of people living within a 3 km radius of a nest knew about its location. The further people they lived from a nest, the less likely they were aware of its presence.

Using what we’d learned in our pilot study, we designed a detailed community-based interview survey method for the 4,150 km2 study area, on which we overlaid 3 x 3 km grid. We conducted 1–3 interviews per grid cell, identifying a total of 53 Pallas’s fish eagle nests. Using this approach, we were able to provide a comprehensive overview of the population and conservation status of Pallas’s fish eagle in north-east Bangladesh, the species’ only stronghold.

Left: Pallas’s Fish Eagle nests in north-east Bangladesh. Right: An adult Pallas’s fish eagle at a wetland in Sunamganj district. Photos: Sayam U. Chowdhury

In addition to identifying nest locations, our results suggest that the eagles prefer to build nests in tall trees with an open canopy structure that are located within or very close to human settlements, and within wetlands or near rivers. We also found a higher nest density in some locations, which we identified as priority conservation areas where immediate conservation actions are required.

The main threat to eagles is the loss of permanent wetlands, but we also found evidence that felling of nest trees, removal of nests by people in retaliation for predation on domestic poultry, and nestlings falling from trees during the nest pre-monsoon storms in March–April cause considerable mortality.

Left: Our Pallas’s fish eagle survey team with the three-wheeler that we used to travel between villages during the survey. Photo: Bangladesh Raptor Research & Conservation Initiative. Right: Interview survey in Sunamganj district, north-east Bangladesh. Photo: Nazim Uddin Khan

Based on these findings, we initiated a nest guardian scheme in villages around Sunamganj city in north-east Bangladesh. This involved the identification of at least one nest guardian for each nest, typically the owner of the nesting tree. We then invited members of nearby households and gave them training on chick handling and rehabilitation, in case any chicks fall from the nest during the pre-monsoon storms.

The high human population density in our study area, and traditional linkages between Pallas’s fish eagle and local communities, allowed us to provide the first comprehensive survey of the species’ breeding population and its habitat requirements in north-east Bangladesh. High nesting density in our study area suggests that the freshwater wetlands of north-east Bangladesh my hold the largest global breeding population of Pallas’s fish eagle. Developing a community-based management plan is the key to the sustained survival of this Endangered eagle in Bangladesh.

The article Using community-based interviews to determine population size, distribution and nest site characteristics of Pallas’s fish eagle in north-east Bangladesh is available in Oryx—The International Journal of Conservation.

Sayam U. Chowdhury is a conservation biologist with interests in the ecology and conservation of threatened species in Asia, and in understanding and mitigating the impact of ecological changes on biodiversity, especially in a densely populated country such as Bangladesh. He is currently a PhD candidate at the University of Cambridge, studying the habitat requirements of threatened shorebirds in the coastal areas of Bangladesh and the multiple factors— such as intense human pressure and climate change—driving their decline.