Is the population of the Critically Endangered white-bellied heron declining in Namdapha Tiger Reserve, India?
ROHAN K. MEN ZIES * 1 , 2 , 3 ,KULBHUSHANSINGH R. S URY AWA NSHI 2 , 4 , 5 and ROHIT NANIWADEKAR 2
Abstract The Critically Endangered white-bellied heron Ardea insignis is a large-bodied, range-restricted, piscivor- ous bird of the Himalayan mountains. With fewer than 60 individuals remaining globally, regular monitoring is re- quired for this rare species.We present the results of surveys during 2017 and 2023–2024 in Namdapha Tiger Reserve, Arunachal Pradesh, India. The encounter rate of white- bellied herons in 2017 was 0.55 individuals per km of river, but we did not detect the bird during intensive surveys in the same location during 2023–2024. The surveyed area within the Reserve was once a stronghold for the species, but its population appears to be declining. Monitoring the population has helped reveal this decline, but identifying and conserving stretches of river still utilized by the re- maining individuals is now critical.
Keywords Ardea insignis, Arunachal Pradesh, conservation status, Eastern Himalaya, India, Namdapha Tiger Reserve, population trends, white-bellied heron
H
erons (family Ardeidae) occur in freshwater and coastal habitats and, because of their longevity and
site-specificity, are considered potential indicators of envir- onmental conditions (Kushlan, 2018). Threats to herons include habitat degradation, hunting and pesticide use, and although they are generally adaptable, nine species and 12% of heron populations are considered threatened (Kushlan, 2007, 2018). A key challenge in heron conser- vation is protecting foraging sites from habitat alteration (Kushlan, 2018, and references therein), and identifying sites occupied annually can be particularly useful for con- servation of threatened heron species (Kushlan, 2007). The white-bellied heron Ardea insignis is categorized as Critically Endangered on the IUCN Red List, with c. 60 individuals estimated to remain globally (Stanley Price &
*Corresponding author,
rohan.cdsmpl2022@
learner.manipal.edu,
rohanmenzies@ncf-india.org 1Manipal Academy of Higher Education, Manipal, India 2Nature Conservation Foundation, Mysore, India 3IUCN Species Survival Commission Heron Specialist Group 4Snow Leopard Trust, Seattle, Washington, USA 5CIFAR Fellow in Future Flourishing Program, MaRS Centre, West Tower, Toronto, Canada
Received 21 May 2024. Revision requested 20 August 2024. Accepted 21 October 2024.
Goodman, 2015; BirdLife International, 2018). The species is regionally extinct in Nepal and possibly extinct in Bangladesh, and its global population is declining (BirdLife International, 2018). Its distribution is patchy across Bhutan, Myanmar and a few locations in north-east India (Stanley Price & Goodman, 2015). Previous studies of the heron have focused on foraging (Mondal &Maheswaran, 2021), breeding (Mondal &Maheswaran, 2014;Acharja, 2020) and anecdotal natural history observations (Maheswaran, 2008). Information on encounter rates or densities of the species that can aid population monitoring is relatively limited (but see Menzies et al., 2021). Since 2016, white-bellied herons in Bhutan appear to no longer re-use nests each year, instead showing a single-use nesting pattern and abandoning older nesting areas, leading to unsuccessful nests in many locations (Acharja, 2020). There are now as few as five breeding pairs in Bhutan (Acharja, 2020). Given its rarity and critical con- servation status, it is imperative to monitor populations of this river bird. There are two known populations of the species: the
western population in Bhutan and the eastern population in the Indo–Myanmar region. The eastern part of Arunachal Pradesh in India, at the junction of the Eastern Himalayas and the Indo–Myanmar region, is an important area for the eastern population. Because of political instability in Myanmar, it is difficult to monitor the population or ensure its protection in the country (Hanson et al., 2009; Goswami & Ganesh, 2014), and thus eastern Arunachal is potentially the last refuge for the eastern pop- ulation of the white-bellied heron. In this region, the 1,985 km2 Namdapha Tiger Reserve, which has harboured low but stable heron populations (Maheswaran, 2008; Menzies et al., 2021), is the largest and most important protected area for the species. Recently, the bird has been reported in areas adjoining Namdapha (Patgiri et al., 2023). During a systematic survey in the central and western parts of Namdapha in 2017 (Menzies et al., 2021) we determined its presence in the Reserve. Here, we report a significant decline in white-bellied heron encounter rates from the central and western parts of Namdapha based on surveys during 2023–2024. We surveyed the Deban, Namdapha and Noa-Dihing
Rivers in Namdapha Tiger Reserve in the Changlang District of Arunachal Pradesh (Fig. 1). In November 2017, as part of the Eastern Himalayan-wide survey of the
This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (
http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution and reproduction, provided the original article is properly cited. Oryx, 2024, 58(6), 730–734 © The Author(s), 2025. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605324001583
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