• Summary
• Text account
• Data table and detailed info
• Distribution map
• Reference and further resources

Justification of Red List category
This species is listed as Endangered precautionarily due to fears it may have a very small population size, comprising fewer than 250 mature individuals, given its confinement to less than 1,000 km² of forest. Should it prove to be more abundant than documented here, it may not be as at high a risk of extinction as feared; however, should it prove to be declining, it may even qualify as Critically Endangered. Future research should endeavour to answer these questions urgently.

Population justification
In 2021, this species had a range that encompassed only 915 km² of forest (per Hansen et al. 2013, Global Forest Watch 2022). Ferguson-Lees and Christie (2001) suggested that S. cheela typically occurs at densities/occupancy as sparse as one pair/100 km², although this is patently not appropriate for this species given the frequency and spread of data (eBird 2022). Instead, a much higher density of one pair/5-6 km² (as also suggested by Ferguson-Lees and Christie [2001] for some Spilornis populations) would give a population size of c.305-370 mature individuals. More recently, Manchi et al. (2021) estimated the density of S. elgini (with which this species is sometimes considered conspecific) to be 4-5 birds/25 km² (=0.16-0.2 birds/km²). This density estimate is considered the most reliable, since S. elgini is sympatric (and thus in competition with) S. cheela, which also applies to the present species. Notably, Manchi et al. (2021) found densities of 7-8 individuals/km² of S. cheela on the Andamans, suggesting that in these circumstances, the possible density of Spilornis species varies little. If the density recorded of S. elgini is true of S. klossi, the species would number only 150-180 mature individuals. Such a low number is broadly congruent with the (perhaps pessimistic) species-specific assessment of Ferguson-Lees and Christie (2001), who wrote of S. klossi that a 'high density would be necessary for [the] population to reach three figures'. There is little reason to suspect that the population density is especially high, with Rasmussen and Anderton (2012) noting that it is 'apparently scarce' and eBird (2022) data suggesting its encounter rate is broadly similar to that of S. elgini. Evaluating the available data, there is high confidence in the fact that this species' population size is likely to be small and this is confirmed by people familiar with the species, who describe it as 'decidedly rare' in the southern half of Great Nicobar and suggest its density may even be lower than that of S. elgini (Praveen J in litt. 2023). The population size is here estimated to be 150-370 mature individuals, with a best estimate of 150-180 (following the data from S. elgini as outlined above).

Trend justification
The only identified threat to this species is habitat loss and degradation. In the three generations (c.24 years; Bird et al. 2020) to 2022, forest loss in this species' range was equivalent to c.4% (using data between 2000 and 2020 and extrapolating) (per Global Forest Watch 2022, based on data from Hansen et al. [2013] and methods disclosed therein). The habitat requirements of this species are improperly known, but it is assumed to be at least somewhat forest dependent (Ferguson-Lees and Christie 2001; Rasmussen and Anderton 2005, 2012). However, most of the losses documented are from Great Nicobar Island, where according to satellite imagery (Google Earth 2022) clearance appears to be small-scale and undertaken by freeholders. Given the adaptability of other Spilornis (see summaries in Ferguson-Lees and Christie 2001, Billerman et al. 2022), it is entirely possible that this scale of habitat degradation does not negatively impact the species, and may even benefit it. Consequently, the population trend is set to unknown.

This species is endemic to the islands of Great Nicobar (including Pulo Kunji), Little Nicobar, Menchal, Pilo Milo and Treis in the South Nicobar island group, Nicobar islands, India (BirdLife International 2001, A. P. Zaibin in litt. 2012). Although there are records from more northerly islands (the 'Central Nicobars') on eBird (2022), these refer to the taxon minimus, which here is tentatively included as a subspecies of the more widespread S. cheeli, but may more appropriately considered a monospecific species (sensu Ferguson-Lees and Christie 2001).

It is found in mixed evergreen forest, and is seen most frequently in the canopy (Rasmussen and Anderton 2012).

Increased settlement of the islands has led to increased pressure on natural resources, and planned development projects (especially to increase tourism) could severely affect the habitat of this species. Nonetheless, this is not yet apparent. In the three generations (c.24 years; Bird et al. 2020) to 2022, forest loss in this species' range was equivalent to c.4% (using data between 2000 and 2020 and extrapolating) (per Global Forest Watch 2022, based on data from Hansen et al. [2013] and methods disclosed therein). The habitat requirements of this species are improperly known, but it is assumed to be at least somewhat forest-dependent (Ferguson-Lees and Christie 2001; Rasmussen and Anderton 2005, 2012). However, most of the losses documented are from Great Nicobar Island, where according to satellite imagery (Google Earth 2022), clearance appears to be small-scale and undertaken by freeholders. Given the adaptability of other Spilornis (see summaries in Ferguson-Lees and Christie 2001, Billerman et al. 2022), it is entirely possible that this scale of habitat degradation does not negatively impact the species, and may even benefit it.

Conservation Actions Underway
None is known, although the species' range is captured in large part by the Great Nicobar Biosphere Reserve (which spans more than 85% of the main island).

Conservation Actions Proposed
The most urgent action for this species is to determine whether its population size is as small as is feared. Surveys similar to Manchi et al. (2021), but targeting the present species, should therefore be considered a priority. It is also critical to understand this species' adaptability to forest degradation, and to investigate whether its population trend is declining. Enforcing protection in the Great Nicobar Biosphere Reserve will be important to safeguarding its future.

Text account compilers
Berryman, A.

Contributors
Ashpole, J, Benstead, P., Crosby, M., Mahood, S., Pande, S., Praveen J, Taylor, J. & Zaibin, A.

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Recommended citation
BirdLife International (2024) Species factsheet: Great Nicobar Serpent-eagle Spilornis klossi. Downloaded from https://datazone.birdlife.org/species/factsheet/great-nicobar-serpent-eagle-spilornis-klossi on 27/11/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from https://datazone.birdlife.org/species/search on 27/11/2024.