- Surveys in Kerala reveal a decline in white-bellied sea eagle nests, mainly due to the loss of tall nesting trees.
- Other coastal states also report loss of the bird’s nesting habitats. However, there is little data on the bird’s population trends in India.
- Researchers in Kerala have adopted a public participatory approach for the bird’s conservation.
In the last few years, there has been a notable decline in the nesting sites of the white-bellied sea eagle in Kerala, raising the need for urgent conservation measures. A report by the Malabar Awareness and Rescue Centre for Wildlife (MARC), an NGO in Kerala’s Kannur district, attributes the loss of nesting sites to felling of the species’ nesting trees, natural ageing or falling of trees.
In 2021, researchers at MARC found 22 nests of the white-bellied sea eagle during their survey in North Kerala. The following year, 2022, the nests declined to 18 and in 2023, the team found only 15 nests.
In Kerala, the white-bellied sea eagle (WBSE) is usually spotted only in two districts in the north, Kannur and Kasargod. Apart from the annual decline seen over the past three years, MARC’s report said that 15 nesting sites found during previous studies between 2000 and 2010, have now been lost, most likely to cutting or natural decline of nesting trees. The white-bellied sea eagles are monogamous and maintain a territory. They have an average lifespan of 30 years, and they reuse the same nest throughout if there is no habitat disturbance.
For the project, the researchers surveyed the 150-km coastline as well as coastal towns, estuaries, backwaters and sacred groves of the two districts during the bird’s breeding season. They also evaluated nesting records from previous studies and from the citizen science database eBird, collected information from local birdwatchers, and from the general public through newspaper announcements. The same methodology was used all three years.
In Kerala’s own regional Red List, the white-bellied sea eagle is currently categorised as having moderate conservation priority. “This was based on the studies until 2010,” say wildlife biologist Roshnath Ramesh and Amal UK, researchers at MARC, who conducted the study. “However, based on our findings now, we have asked to change its categorisation to high priority.” The regional Red List, prepared by the Zoological Survey of India’s Western Ghat Regional Centre with inputs from other experts, was published by the Kerala State Biodiversity Board in 2023. The document follows the guidelines of IUCN regional level assessment and also gives a priority list of species for local conservation.
The white-bellied sea eagle is a keystone species in coastal areas. As an apex predator, it has a critical role in maintaining the health of the ecosystem. A healthy population of the white-bellied sea eagle is considered a good indicator of the ecosystem’s health as well. The bird is seen in the South and Southeast Asian coasts, up till Australia.
Though the International Union for Conservation of Nature (IUCN) Red List lists white-bellied sea eagle in the least concern category, it mentions that the bird’s population is suspected to be reducing globally, especially in regions like South Australia. Though there is no clear data on the bird’s population, global numbers are estimated to be in the range of 2,600-41,000 mature individuals.
In India, data from the citizen science database, eBird, shows a steep fall in sightings over the long term. According to the State of India’s Birds (SoIB) report, 2023, – which is based on the eBird database – the long-term trend shows that the white-bellied sea eagle sightings have declined by two-thirds compared to the pre-2000 baseline. SoIB has listed the species in the ‘moderate concern’ category.
Shifting habitats
Researchers in states such as Odisha and Maharashtra report loss of the bird’s habitat, which can reduce nest productivity and impact its population.
The white-bellied sea eagles tend to nest on tall trees such as banyan, casuarina and mango near the coast, from where the sea would be visible. “This bird forages from the surface of the sea; it doesn’t dive in,” says Babu S, Senior Scientist at the Salim Ali Centre for Ornithology and Natural History (SACON). “So, it seems to select trees from where the sea is visible.” With the loss of tall trees along the coast, the species is faced with the loss of nesting sites.
In Odisha, researchers are increasingly seeing the white-bellied sea eagles switching to alternative habitats. In an ongoing study, that is yet to be published, researchers from Berhampur University found only a quarter of the white-bellied sea eagle nests in natural habitats. The remaining three-quarters were found on cell phone towers, power transmission towers, etc. “Over 150 white-bellied sea eagles have been identified in Ganjam, Khurda and Puri districts under the study, and more nests are likely to be identified once the study covers the rest of the Odisha coast,” B. Anjan Kumar Prusty, Conservation Ecologist and Professor at the Department of Environmental Science at Berhampur University, who is also supervising the study, says “The nests on cell phone towers indicate the loss of the bird’s original habitat, mostly due to cyclones and/or human interventions. “The number of cyclones and extreme weather events and their periodicity are increasing due to climate change as well. The birds do not seem to prefer moving too far inland, possibly to avoid competition with other bird species for resources such as food and foraging ground.”
Another survey done in the Bhitarkanika National Park in coastal Odisha in 2018-2019 had shown that out of the 10 white-bellied sea eagles nests identified, five were on cell phone towers and two on dead trees. The study published in the journal, E-Planet, said the nesting sites were disturbed by human activity. It added that depleting fish stocks in the sanctuary, along with water contamination by oil spills from fishing/tourist boats can also threaten the birds.
Nimain Charan Palei, corresponding author of the study and a biologist, mentions another risk factor. “White-bellied sea eagles move up to 10-15 kilometre inland to prey on fish in wetlands, estuaries, etc. Within this radius, pesticides are used in farms and prawn factories here, which pollutes the nearby water bodies. So white-bellied sea eagles that catch fish from these water bodies can get exposed to pesticides.”
Research papers from other coastal states like Tamil Nadu and Andhra Pradesh have also documented the eagle nests on pylons and cell phone towers.
In Maharashtra too, conservationists are seeing habitat shifts over time.
Vishwas Katdare, founder of Sahyadri Nisarga Mitra (SNM), an NGO that led white-bellied sea eagle surveys in Ratnagiri and Sindhudurg districts of Maharashtra between 1996 and 2000, says these birds have shifted their nests to smaller trees over time. “Earlier, they used to nest in large, old trees,” he added. “Due to natural calamities or felling of these trees, they have been forced to shift to small trees, which are less stable for their large nests.”
A 2020-2021 survey in Ratnagiri and Raigad, Maharashtra, by the NGO Mangrove Foundation, also showed that the bird’s nesting patterns changed after Cyclone Nisarga of June 2020. Mohan Upadhye, part of the team that conducted the survey, says, “Before the cyclone, these birds used to nest at the height of 80-100 feet. When tall trees were damaged in the cyclone, they rebuilt nests in shorter trees, at the height of 30-40 feet.”
Babu from Salim Ali Centre for Ornithology and Natural History (SACON), who studied white-bellied sea eagles in Sindhudurg, Maharashtra, says the number of nests had increased to 46 at the time of his survey in 2014-2017, compared to SNM’s count of 32 in 1999-2000. He attributes the increase in nests to the increase in the number of matured casuarina plantations on the district’s coastline over the years. Even then, casuarina plantations on coastal areas tend to be logged, which would damage the species’ habitats. Hence the study suggested planting native trees, or a mix of native and exotic plantations in coastal areas, along with reducing recreational activities in beaches, to avoid disturbances to nesting white-bellied sea eagles.
Researchers call for better monitoring, baseline data
Despite the increasing threats to the white-bellied sea eagles in India, there have been no national-level studies on its population trends. Hence, scientists across coastal states have been calling for the collection of reliable baseline data, along with regular nest monitoring.
MARC’s report from Kerala suggests further studies such as bird ringing and banding to find their home and dispersal range, species distribution modelling, short-distance pelagic surveys, etc. Ramesh, who is also the Secretary at MARC, says, “We have a hypothesis that as sea temperature increases and productivity reduces, the white-bellied sea eagles in Kerala are moving north towards Mangalore in line with sardine availability. This could be a reason for their declining population in Kerala. However, we need data to establish this.”
Suresh Kumar, wildlife biologist and Scientist-F at the Wildlife Institute of India, says that the species should be studied in view of the declining sightings nationally as well as reports about changes at the local level. He adds that the population of fish eagles is declining worldwide.
In some coastal areas, comprehensive surveys are being taken up. In Maharashtra, SNM is planning to repeat their survey after a gap of over 20 years, to understand the change in the bird’s status.
In Goa, conservation NGOs are conducting a survey in coordination with the state forest department and state biodiversity board. Parag Ranganekar of the Goa Bird Conservation Network, who is leading the project, says this is the first survey of the bird in Goa. “We have been planning to do this survey for a while, but the declining trend mentioned in the SoIB report was the trigger,” he adds. “We do not have any data-backed evidence about the white-bellied sea eagle now. Once we establish a baseline through this survey, we can continue to monitor the nests.” As of November 2024, the team had identified 24 nests.
A promising conservation model
In Kerala, MARC has implemented a community-based conservation programme to protect the white-bellied sea eagles. The programme honours stakeholders in the community, such as owners of trees having the bird’s nests, fishermen and others who monitor nests and pass on information. A WhatsApp group of about 30 people share information and photos of the nests regularly.
Since the white-bellied sea eagles’ nests are mostly located in urban spaces, conservation has to involve the public, says Ramesh. “Fishermen are actively involved as they are familiar with the bird and can identify it by its call,” he adds. “Owners of nesting trees also call us in case of any concerns about the trees.”
At Chal beach in Kannur district, a group of 3-4 local conservationists are protecting one of the nests under this programme. Shijil Kottayi, a fisherman, and Sunil Arippa, a pharmacist, are among the group members who visit a nesting tree on the beach daily. “We have been seeing these birds here for a few years, but we learnt about the species and found their nest after MARC’s survey,” they say. “There are no direct threats to the birds here, but we ensure no one is bothering them and that the tree is not affected during rains.”
Lakshmanan T. who lives in Ramanthali of Kannur district and is also part of the programme, owns a plot of land where a nesting tree stands. He says, “Until a few years ago, 3-4 white-bellied sea eagles used to nest on tall trees close to the beach here. Over time, the owners cut these trees. Now only one pair of the birds is left. About four years ago, they nested in a tall tree on my property, which is one kilometre away from the beach.”
Though the tree is at risk of falling and damaging his house during strong winds, Lakshmanan says he is ready to wait for now. “I was planning to cut the tree earlier, but as part of the programme I am conserving it now,” he adds. “I will see if this pair of birds will move out as some other pairs have in the neighbouring properties.”
In Goa, Ranganekar shares plans to implement a similar programme after their survey. The team is also planning to get the nesting trees included in the People’s Biodiversity Registers (PBRs) of the local Biodiversity Management Committees (BMCs) for their conservation.
Banner image: A white-bellied sea eagle flying over Chal beach, Kannur, Kerala. The beach has just one nest, which is one of the two remaining nests in the district. Image by Anil Prasad.
Credits
