Using community-based interviews to determine population size, distribution and nest site characteristics of Pallas's fish eagle in north-east Bangladesh S AY AM U. CHOWDHURY,MOHAMMOD FOY S A L and NAZ IM UDDIN KHAN
Abstract Pallas’s fish eagle Haliaeetus leucoryphus was re- categorized from Vulnerable to Endangered on the IUCN Red List in 2017 because of evidence that there is only a single population, which is declining as a result of con- tinuous, widespread loss and degradation of freshwater wet- lands. To determine the species’ status in Bangladesh, we conducted a large-scale community-based interview survey in north-east Bangladesh in 2017–2020. We also examined nest site habitat characteristics through field surveys and re- motely sensed data. We conducted a total of 955 interviews in an area of 4,150 km2, through which we were able to de- termine the presence of 53 breeding pairs at a mean density of 1.2 nests per 100 km2. There was a higher nest density (3.7–4.8 nests per 100 km2) in some locations, which we identify as priority conservation areas. The majority of nests (62.2%) were close together and on tall trees with an open canopy structure. Nests were located within or close to (,100 m) human settlements, and within 500 m of wet- lands and rivers. Felling of nest trees, removal of nests by local people and loss of permanent wetlands (14.6% during 2010–2020) appeared to be the main threats. High nesting density in our study area suggests that the freshwater wet- lands in north-east Bangladesh possibly hold the largest population of Pallas’s fish eagle globally.
Keywords Bangladesh, community-based interviews, con- servation, Endangered, Haliaeetus leucoryphus, raptor, Pallas’s fish eagle, wetlands
Supplementary material for this article is available at
doi.org/10.1017/S0030605321000314
Introduction
out Asia, particularly in north-east India and Bangladesh (Cripps, 1878; BirdLife International, 2001). In 2017 the species was recategorized from Vulnerable to Endangered on the IUCN Red List, with a global population estimate of 1,000–2,499 mature individuals (BirdLife International, 2020). The reason for this reassessment was primarily the continuous and widespread loss, degradation and distur- bance of freshwater wetlands throughout the species’ range, and new evidence that there is only a single, migra- tory population (Gilbert et al., 2014; Steele, 2017). Prior to the recategorization of the species’ conservation
P
status, the rate of population decline was assumed to be lower than it actually was (BirdLife International, 2020). It was believed that the species comprised several isolated sub- populations, including a migratory breeding subpopula- tion north of the Himalayas in Mongolia and surrounding countries, and a non-migratory, resident breeding subpopu- lation south of the Himalayas in the Indian subcontinent. However, there is little evidence of breeding north of the Himalayas, and the supposedly separate populations south and north of the Himalayas are in fact a single migratory population that breeds in the Indian subcontinent in winter (October–April) and migrates north of the Himalayas, no- tably to Mongolia, in the summer (May–September; Naoroji, 2006; Gilbert et al., 2014; Steele, 2017; BirdLife International, 2020). Current knowledge suggests that the breeding range of Pallas’s fish eagle encompasses India, Bangladesh, Nepal, Bhutan and possibly also Myanmar (Steele, 2017; BirdLife International, 2020). Based on previ- ous observations (Naher & Khan 2009; Sourav et al., 2011) and ad hoc records (SUC, unpubl. data, 2017) in north-east Bangladesh, we hypothesized that this region could be globally important for the species. The study of small and isolated animal populations is
SAYAM U. CHOWDHURY* (Corresponding author,
orcid.org/0000-0002-1901-
8900,
sayam_uc@yahoo.com), MOHAMMOD FOYSAL and NAZIM UDDIN KHAN Bangladesh Raptor Research and Conservation Initiative, 16/C Tallabag, Sobhanbag, Mohammadpur, Dhaka 1207, Bangladesh
*Also at: Conservation Science Group, Department of Zoology, University of Cambridge, Cambridge, UK
Received 27 July 2020. Revision requested 15 October 2020. Accepted 10 March 2021. First published online 20 December 2021.
often difficult, expensive and time-consuming using stan- dard survey techniques (Turvey et al., 2016). Alternative and adaptive survey methods may therefore be necessary to determine the population status of threatened species (Turvey et al., 2014; Nash et al., 2016). Interview-based surveys that utilize the knowledge and experience of local people can be useful and are likely to provide accurate
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 in any medium, provided the original work is properly cited. Oryx, 2022, 56(4), 627–635 © The Author(s), 2021. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605321000314
allas’s fish eagle Haliaeetus leucoryphus was abundant in the 19th century along freshwater sources through-
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