Journal of Threatened Taxa | www.threatenedtaxa.org | 26 June 2026 | 18(6): 29138–29142

ISSN 0974-7907 (Online) | ISSN 0974-7893 (Print)

https://doi.org/10.11609/jott.10547.18.6.29138-29142

#10547 | Received 23 March 2026 | Final received 17 April 2026| Finally accepted 05 May 2026

Rapid increase in artificial-substrate nesting by White-bellied Sea Eagle Haliaeetus leucogaster (Gmelin, 1788) (Aves: Accipitriformes: Accipitridae) in Tamil Nadu, India

H. Byju ¹, N. Raveendran ² & H. Maitreyi ³

^1,3 Centre of Advanced Study in Marine Biology, Annamalai University, Parangipettai, Tamil Nadu 608502, India.

² Iragukal Amritha Nature Trust, 61, Ramachandra Thadaga Street, Thirumangalam, Madurai, Tamil Nadu 625706, India.

¹ byjuhi@gmail.com (corresponding author), ² Iant.ravee@gmail.com, ³ maithgd@gmail.com

Editor: Anil Kumar, Zoological Survey of India, Patna, India. Date of publication: 26 June 2026 (online & print)

Citation: Byju, H., N. Raveendran & H. Maitreyi (2026). Rapid increase in artificial-substrate nesting by White-bellied Sea Eagle Haliaeetus leucogaster (Gmelin, 1788) (Aves: Accipitriformes: Accipitridae) in Tamil Nadu. Journal of Threatened Taxa 18(6): 29138–29142. https://doi.org/10.11609/jott.10547.18.6.29138-29142

Copyright: © Byju et al. 2026. Creative Commons Attribution 4.0 International License. JoTT allows unrestricted use, reproduction, and distribution of this article in any medium by providing adequate credit to the author(s) and the source of publication.

Funding: None.

Competing interests: The authors declare no competing interests.

Abstract: White-bellied Sea Eagle Haliaeetus leucogaster is a coastal apex predator whose nesting ecology is associated with the availability of tall trees along water bodies. An increase in anthropogenic pressure along the southeastern coast of India has led to nesting adaptations, including the use of artificial substrates. Here, unusual observations on four nests constructed on artificial structures within a single breeding season (2025–2026) in Ramanathapuram District, Tamil Nadu, of which three were successful are reported. Only one artificial substrate nest was recorded in the previous decade. This represents a notable increase compared to previous records from the region and suggests a potential behavioural shift. Nesting activity patterns, breeding success, and conservation implications in the context of habitat modification and ecological traps are discussed.

Keywords: Apex predator, breeding, coastal wetland, electric pylon, nest-site selection, raptor, Ramanathapuram.

The White-bellied Sea Eagle (WBSE) Haliaeetus leucogaster is a large, diurnal raptor distributed across the coastal regions of the Indian subcontinent, southeastern Asia, and Australia (del Hoyo et al. 1994). As a sentinel species of ecosystem health, its presence and breeding success are key indicators of thriving coastal and wetland habitats (Amal & Roshnath 2025). Traditionally, WBSEs exhibit high nest-site fidelity, constructing large, stick-platform nests (eyries) in the upper canopies of tall, mature trees, which provide security from terrestrial predators and afford optimal vantage points for foraging (Azman et al. 2013). WBSE accounts of nesting on communication towers or windmills are reported from Australia and Thailand, but documentation from the Indian subcontinent remains scarce (Palei et al. 2014). Although with increasing frequency of nesting from Odisha (Pattnayak et al. 2025a) and Tamil Nadu (Byju et al. 2023a), they prefer to nest on electric pylons and telecommunication towers. Habitat loss resulting from the decline of mature coastal trees due to urbanization, cyclones, and shoreline development has forced the species to increasingly adopt artificial nesting substrates (Byju et al. 2023a; Pattnayak et al. 2025a). Artificial nesting may represent behavioural plasticity, emerging evidence suggests that these structures may function as ecological traps, often associated with lower breeding success and higher mortality risks (Pattnayak et al. 2025a). This study documents an unusual clustering of nests on artificial substrates in Ramanathapuram, contributing to the growing body of evidence on this adaptive shift and its conservation implications.

Study area

The observations were made along the coastal belt of Ramanathapuram District, southeastern Tamil Nadu (Figure 1). The region comprises a mosaic of tidal creeks, mudflats, aquaculture ponds, and fragmented coastal vegetation. The area has undergone substantial land-use change, including the loss of mature nesting trees, expansion of aquaculture and increased human settlement and infrastructure. Such changes are likely influencing nesting site selection by WBSEs.

Methods

Field observations were carried out during the breeding season (November–March) of 2025–2026, following roadside surveys are described in the previous study (Byju et al 2023a). Nests built on artificial substrates (n = 4) were monitored at least once every 10 days to assess occupancy, breeding activity (pair presence, incubation, and nestling rearing), outcomes (success/failure), and fledging rates. Behavioural observations included nest-building, prey delivery, and defensive responses. A nest was considered successful if at least one chick survived the fledging stage (~80 days for WBSE), which represents a key threshold for independent survival (Debus 2008; Dennis et al. 2012), irrespective of parental care. Nests were classified as unsuccessful if they were abandoned during any stage or if no nestlings reached fledging. Observations were made from 50 m to 100 m using binoculars and spotting scopes to mitigate disturbance. Abandonment was confirmed when repeated visits showed no adult presence, absence of nest maintenance, and no evidence of chicks (Liu et al. 2009).

Results and Discussion

Nest distribution and success

A total of four nests (N1–N4) were recorded on artificial substrates within a relatively small spatial extent. Three nests were active and successful, producing chicks (Table 1). One nest (N4) functioned as a secondary or alternate nest. This represents an unusually high density of artificial-substrate nesting for the region within a single breeding season. The height of the nest in the pylon and towers was approximately 18 m from ground level (Byju et al. 2023a).

Behavioural observations

Adults were observed reinforcing nests with sticks, indicating prolonged prior use of certain nests (N1) before egg-laying, whereas the other nests appeared to have been constructed in the months leading up to egg-laying. Use of multiple nests (including a non-breeding ‘false nest’) was recorded in the first observation (Byju et al. 2023a), likely as a predator avoidance strategy, and was not recorded in the current year’s observations. Feeding consisted predominantly of fish, consistent with the species’ foraging behaviour.

Breeding success

Interestingly, 75% nesting success (3/4 nests) in this observation contrasts with larger-scale studies indicating a lower fledging success on artificial structures and up to 39% failure rates on pylons (0.87 fledglings per attempt) compared to near 100% (higher productivity, 1.74 fledglings per attempt) in natural trees (Pattnayak et al. 2025b). This discrepancy may be due to proximity to productive foraging habitats, lower disturbance levels at specific sites and early-stage adaptation before long-term negative effects manifest. Higher fledgling rates may be due to the proximity of a water body adjoining the nests (N1 and N2 had two chicks compared to N3 with one chick). In principle, a closer foraging site can reduce foraging time and energy expenditure, enhance the delivery of fish or other aquatic prey to the nest, and thus increase nestlings’ survival (Pattnayak et al. 2025b).

Artificial structures as potential ecological traps

The shift in nesting patterns is likely driven by the decline of mature coastal trees due to developmental activities and cyclone impacts. At the same time, expanding infrastructure has introduced elevated artificial structures that offer alternative nesting sites. Similar trends have been reported from eastern India, where habitat alteration influences raptor breeding ecology (Palei et al. 2022). Breeding outcomes differ markedly between natural and artificial sites, suggesting that many artificial structures function as ecological traps (Pattnayak et al. 2025a). These sites are often located in disturbed environments, closer to roads and human settlements, where increased disturbance can elevate stress, disrupt foraging and lower long-term reproductive success (Bilney & Emison 1983). Therefore, although artificial structures may compensate for the loss of nesting sites in the short term, they are unlikely to sustain healthy population growth over the long term.

Conservation implications

The observations highlight both opportunity and concern. The opportunities include alternative nesting substrates in landscapes where natural sites are irrevocably decreased or lost; these structures can provide essential nesting platforms, potentially preventing local breeding collapse. This can lead to conservation partnerships with infrastructure companies (power utilities, telecom). This can be leveraged for collaborative conservation, such as ‘raptor-friendly’ infrastructure design.

Meanwhile, severe threats include electrocution as a paramount risk. WBSEs have large wingspans (~1.8–2.2 m). Nesting on or taking off from live power pylons poses a high probability of wing-to-conductor or conductor-to-ground electrocution, a leading cause of mortality for raptors globally (Jenkins et al. 2010; Manigandan et al. 2021). Collisions with wires supporting communication towers are often invisible to fast-flying birds, leading to fatal strikes. Chicks are at risk of falling or exposure to extreme weather from nest platforms on towers, which are often smaller, more exposed, and less stable than those of natural tree nests.

Recommendations

Proactive, evidence-based management is required, including an urgent need for a district-wide systemic survey to map all WBSE nests (natural and artificial) to assess the scale of artificial nests. To mitigate risk at nest sites, collaboration with electricity distribution companies (e.g., TANGEDCO) can enable retrofitting of active pylon nests with insulated covers or perch deterrents on live components. For communication towers, bird-flight diverters on guy wires can be installed. A promising strategy is the erection of purpose-built, safe artificial nest platforms (ANPs) on tall poles in secure locations near foraging areas. These ANPs can be designed to be more attractive (stable, spacious) and safer than power towers. Long-term conservation must focus on protecting and restoring mangrove corridors with large, old trees to support natural nesting, as this region is already having the first Asian record of Light-mantled Albatross Phoebetria palpebrata (Byju & Raveendran 2022), breeding of Noddy (Byju et al. 2025a), Terns (Byju et al. 2025b) and regional endemic Hanuman Plover Anarhynchus seebohmi (Byju et al. 2023b). Continuous engagement with local communities, fisherfolk, and infrastructure managers is crucial to building stewardship and reporting nesting activity.

Conclusion

The documentation of four nests of WBSEs on artificial structures, with three successful breeding attempts, represents a significant and possibly emerging trend in Ramanathapuram. While this behaviour reflects adaptability to changing landscapes, it also signals underlying habitat degradation. It is a clear ecological signal of habitat transformation and species adaptability. Understanding whether such nesting strategies represent a sustainable adaptation or a potential ecological trap is critical. Continued monitoring and targeted conservation interventions are essential to ensure the long-term survival of this iconic coastal raptor.

Table 1. Four nests of White-bellied Sea Eagle with their breeding biology and nest locations.

Nest ID	Substrate type	Status	Breeding cycle	Outcome	Notable behaviour	GPS location
N1	Electric	Active (same nest as in 2022–2023)	Chick reared -2	Successful	Strong territorial defense	9.289° N, 78.998° E
N2	Telecommunication tower	Active	Chick reared -2	Successful	Regular prey delivery (fish)	9.285° N, 79.064° E
N3	Telecommunication tower	Active	Chick reared -1	Successful	Nest repair observed	9.310° N, 79.003° E
N4	Telecommunication tower	Secondary	Nest built; no eggs	Unsuccessful	Secondary/inactive	9.278° N, 79.152° E

Note: Active nests have egg-laying confirmed.

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