Journal of Threatened
Taxa | www.threatenedtaxa.org | 26 May 2026 | 18(5): 28971–28975
ISSN 0974-7907 (Online) | ISSN 0974-7893 (Print)
https://doi.org/10.11609/jott.10236.18.5.28971-28975
#10236 | Received 01 November 2025| Final received 10 February 2026|
Finally accepted 17 April 2026
Preliminary observations on the
breeding ecology and potential threats to Bonelli’s
Eagle Aquila fasciata in Sithagiri
Malai, Tamil Nadu, India
S. Naveenkumar
1 , H. Byju
2 & H. Maitreyi 3
1 439, 6th Street, K.K. Pudur, Coimbatore, Tamil Nadu 641038, India.
2,3 Centre of Advanced Study in
Marine Biology, Annamalai University, Parangipettai,
Tamil Nadu 608502, India.
1 naturenks@gmail.com, 2 byjuhi@gmail.com
(corresponding author), 3 maithgd@gmail.com
Editor: Thilina Nethmin de Silva,
University of Utah, Salt Lake City, USA. Date
of publication: 26 May 2026 (online & print)
Citation: Naveenkumar, S., H. Byju & H.
Maitreyi (2026). Preliminary observations
on the breeding ecology and potential threats to Bonelli’s
Eagle Aquila fasciata in Sithagiri
Malai, Tamil Nadu, India. Journal of Threatened Taxa 18(5): 28971–28975. https://doi.org/10.11609/jott.10236.18.5.28971-28975
Copyright: © Naveenkumar 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.
Acknowledgments: We thank Mr. Kuppusamy, the grandfather of the first author for providing information about the traditional aspects of Sithagiri Malai and informing the presence of Bonelli’s Eagle.
Abstract: Bonelli’s Eagle (Mosaladikki;
meaning hare hunter) Aquila fasciata is a top
predator experiencing population declines across its range. This study presents
preliminary findings from a periodic survey (April 2024–May 2025) in Sithagiri Malai, a rocky outcrop
in Tamil Nadu, India. We document the presence of breeding territory, potential
prey species, and discuss imminent threats, particularly from windmills, emphasising the ecological value of rocky outcrops for the
species in this landscape.
Keywords: Accipitridae, Accipitriformes,
bioindicators, power line collisions, raptors, rock outcrop, wind turbines.
Raptors are indicators of
environmental health and are keystone species (Kitowski et al. 2017), vital for
maintaining ecosystem balance. As apex predators, they help regulate prey
populations, preventing overgrazing, and agricultural damage (Donázar et al. 2016). Globally, 18% of raptors are
threatened with extinction and 52% exhibit declining populations (McClure et
al. 2018), making demographic studies crucial for their conservation (Byju et al. 2023).
The Bonelli’s
Eagle Aquila fasciata is an uncommon resident
throughout the Indian subcontinent from plains to 2,600 m (Ali & Ripley
1987; Rasmussen & Anderton 2012). It is a cliff-nesting raptor with
fragmented distribution across the Palearctic, Indo-Malayan, and marginally
Afrotropical regions (Di Vittorio et al. 2017; Birdlife International 2020).
Breeding period varied in the western range (January–July); Indo-Malayan region
(November–September) (Ferguson-Lees & Christie 2001), and Indian region
(December–May) (Ali & Ripley 1987; Ontiveros 1999; Rasmussen & Anderton
2012). Bonelli’s Eagle is a long-lived, territorial,
and monogamous species. The nest is a massive platform built on cliffs or on
tall trees and reused in successive years (Hernández-Matías
et al. 2011). Rocky outcrops provide critical nesting habitat for this species,
offering inaccessible cliff faces that protect nests from mammalian predators
(Fitzsimons & Michael 2017).
The population is declining
drastically throughout its range owing to over-use of pesticides, habitat
degradation, loss of prey species, collision with power lines, and persecution
by hunters & pigeon fanciers (Ferguson-Lees & Christie 2001; Bharos & Pare 2023). This study reports initial
observations on Bonelli’s Eagle breeding in Sithagiri Malai, focusing on its
potential threats. This study emphasizes the conservation significance of this
rocky hillock as a potential breeding area for birds, despite growing
anthropogenic pressures, including rock mining in the vicinity.
Observations
Breeding was recorded in Sithagiri Malai, Kuppanavalasu, Tamil Nadu (approx. 10.450 N,
77.720 E), a rocky outcrop with elevations ranging from 287–376 m
(Image 1). This hill supports moderate dry-deciduous scrub vegetation. Sithagiri Malai comprises at
least three sacred temples, one of which is a cave temple that hosts a bat
population. Natural water holes locally called ‘Paali’
and ‘Sonai’ are present here; the former has served
as a water source for people and cattle, and the latter is used as a sacred
water to treat illness until the mid-20th Century. The area is
surrounded by grasslands either with bio-fences or fenced with granite poles,
agricultural lands, and villages. The region receives the north-east monsoon
from October–December, and summers last from March–June with occasional summer
showers. Geographically, it lies ~100 km east of the Palakkad Gap, leading to
strong westerly winds during the south-west monsoon season
(June–September).
Field visits were carried out from
April 2024 to May 2025, at fortnightly intervals, every month. The bird’s
behaviour was recorded from 0700–0900 h and 1600–1800 h. Observation was
carried out at a distance of at least 250 m to avoid disturbance through a
Nikon Aculon binocular (8 × 42). Photographic documentation was done using a
Nikon P950 camera.
With information from local
villagers, the activity of Bonelli’s Eagle was
followed. We confirmed the first breeding record of this species from the area,
and the breeding season is from December–March (Bharos
& Pare 2023). A detailed chronological follow-up of some field observations
of nesting details is given separately in Table 1. Sithagiri
Malai breeding territory is consistent with the
species’ preference for rocky, arid to semi-moist habitats (Ferguson-Lees &
Christie 2001). A nest, composed of sticks and approximately 1.5 m in diameter,
was located on a remote cliff ledge (Image 2). The surrounding landscape,
including grasslands and agricultural fields, likely serves as foraging areas,
as eagles often hunt several kilometers from the
nest.
Adult male is dark brown above with
a capped head and a white patch on the back. The tail is grey, obscurely
barred, with a broad sub-terminal band; white below with thin streaks, broader
on breast/flanks, bars on belly/crissum. During flight, below the white body, a
black band on the linings; obscure dark trailing edges to greyish remiges; a
subterminal band on paler tail. Above white on back; grey tail, dark band.
Adult female—flight below smaller; quills more clearly barred;
belly/thighs/crissum more boldly marked (Ferguson-Lees & Christie 2001).
From both our field observations
and local villagers’ accounts, the potential prey species identified included
Indian Hare Lepus nigricollis, Bonnet Macaque Macaca radiata, Grey Francolin Ortygornis pondicerianus,
Rock Bush Quail Perdicula argoondah, and domestic poultry. The presence of the
Grey Slender Loris Loris lydekkerianus and Bengal Monitor Lizard Varanus bengalensis
suggests a diverse prey base (Image 3). Potential predators of the eagle chicks
include Indian Golden Jackal Canis aureus,
Jungle Cat Felis Chaus,
and Rock Eagle-Owl Bubo bengalensis, the
latter being a known predator of Bonelli’s Eagle
chicks in other regions (Image 4).
Potential Conservation Threats
The primary threats identified are
linked to energy infrastructure and habitat modification.
Bonelli’s Eagle nesting area is in proximity
to windmills, and the birds are often observed flying around it for foraging.
The region’s high wind potential, ideal for energy development, poses collision
risks for raptors like Bonelli’s Eagle, which engage
in kiting and stooping while hunting (Smallwood & Thelander
2008; Skarabal et al. 2025), limiting maneuverability, and increasing collision risk (De Lucas et
al. 2008), as they might lose track of their wind turbine position (Krijgsveld et al. 2009). While the present study focuses on
nesting ecology rather than mortality assessment, the proximity of active wind
turbines to known nesting and flight corridors warrants caution. Incorporating
bird flight height data and seasonal activity patterns could help avert future
bird and bat collision risk assessments, which would be essential for
accurately quantifying turbine-related threats to Bonelli’s
Eagle populations in the Dindigul landscape. In the
Western Ghats (Karnataka and Maharashtra), most victims of this collision were
land birds such as Bonelli’s Eagle, Changeable Hawk
Eagle Nisaetus cirrhatus,
and Black Kite Milvus migrans (Kumar et al.
2019, 2022).
Electrocution on poorly designed
power pylons and collision with power lines are leading causes of mortality for
Bonelli’s Eagles globally (Hernández-Matías et al. 2015). Even though we did not observe any
electrocution of the species, the existing and expanding network of electric
pylons in the landscape poses a potential risk, as electrocution of raptors is
increasingly reported (Manigandan et al. 2022). The
conversion of traditional bio-fences to impermeable granite stone walls reduces
microhabitats for prey species. The sacred and cultural significance of Sithagiri Malai (e.g., cave
temples, water holes) may offer some protection, but rising anthropogenic
pressure remains a concern. The emerging threat to this rocky outcrop is the
potential impact of climate change, as species inhabiting mountain regions are
predicted to be adversely affected by rising temperatures and reductions in
bioavailable water (Fitzsimons & Michael 2017). Cattle grazing and firewood
collection are not observed, but bird poaching is still reported by locals,
along with honey gathering. Presently, there is no mining, but we observed that
the sounds created by nearby rock mines created panic for peafowls. This is not
impacting the nesting of eagles, at present. The bio-fence of the
grassland patch, which is being converted to a metal fence with granite stone,
is reducing hiding spots for several reptile, mammal, and bird species.
Currently, no conservation outreach, either by villagers or NGOs, is active.
Hence, immediate conservation measures are warranted.
Conclusion
Sithagiri Malai
provides a critical breeding habitat for the Bonelli’s
Eagle in Tamil Nadu. The confirmed nesting site and diverse prey base highlight
this rocky outcrop ecosystem’s high conservation value.
Table 1. Summary of observations
on the nesting
Bonelli’s Eagle.
|
Date of observation |
Time of observation |
Activities and behaviour |
|
09.iv.2024 |
0700−0900 h |
Two adult birds were taking
advantage of the thermal current upwind and actively scanning for prey. Then
the female bird perched on the rocks looking for food. |
|
18.viii.2024 |
0700–0900 h |
Observed both male and female
roosting on a single tree. Remnants of an old nest are observed on the rock
cliff. |
|
29.xii.2024 |
0700–0900 h |
One adult was observed roosting
in a tree and grooming. |
|
16.i.2025 |
0700–0900 h |
Nest looks in good shape with a
reinforced base on an inaccessible cliff face. Approximately 1.5 m in
diameter. |
|
22.ii.2025 |
0700–0900 h |
The male was perched on the
rock in the vicinity of the nest. The female was seen inside the nest; chicks
or eggs were not visible. |
|
27.iii.2025 |
1600–1800 h |
Two fledglings were seen inside
the nest with dropped wings. A male was seen guarding the nest from the rock
situated above it. |
|
28.iii.2025 |
0700–0900 h |
The female was feeding two
chicks inside the nest. Prey was recorded from the bottom of the cliff. |
|
26.iv.2025 |
0700–0900, 1600–1800 h |
Initially, the fledglings,
which have become juveniles, were seen with adults in flight. Then, one
juvenile was seen roosting in a tree. The juveniles were seen soaring very
close to the adults. On the ground, the juveniles were still dependent on the
adult for food. |
|
15.v.2025 |
0700–0900 h |
Two of the juveniles were
flying together and engaged in aerial combat a couple of times. One was
trying to catch an Asian Palm Swift. At previous night, the nearest temple
had crackers for the festival. |
For images - - click here for
full PDF
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