The white‐bellied heron in India 731
FIG. 1 Namdapha Tiger Reserve, Arunachal Pradesh, India, where we surveyed the Deban, Namdapha and Noa-Dihing Rivers during November 2017 (Menzies et al., 2021) and November 2023–March 2024 (this study) to record sightings of the white-bellied heron Ardea insignis.
TABLE 1 White-bellied heron Ardea insignis detections and encounter rates from line transect surveys in Namdapha Tiger Reserve during 2014–2024.
Survey Mondal (2018) Duration
Menzies et al. (2021) Nov. 2017 This study This study
Feb. 2023
No. of transects
Nov. 2014–Jan. 2017 65 7 5
Nov. 2023–Mar. 2024 90
Mean length (km)
0.62 1.80 5.93 0.50
Total effort (km)
40.0 12.6 29.7 45.0
Total
detections 7
6 0 0
Total
individuals 8
7 0 0
Encounter rate (per km)
0.20* 0.55 0.00 0.00
*The author used total detections divided by effort to calculate an encounter rate of 0.175, meaning multiple individuals encountered on a single occasion were recorded as a single detection. Here we use total individuals sighted divided by effort, adjusting this encounter rate to 0.20.
white-bellied heron (Menzies et al., 2021), we surveyed seven 0.6–2km long transects, with a total survey effort of 12.6 km. In February 2023,we surveyed five 3.8–7.7kmlong transects, with a total effort of 29.7 km, and during November 2023–March 2024 we surveyed 18 0.5 km transects five times each, with a total effort of 45 km (Table 1). We re- corded all sightings (perched or flying) of the white-bellied heron during and outside the transect walks (Plate 1). During our surveys in 2017 we recorded seven herons, with
a mean encounter rate of 0.55 ± SE 0.24 individuals per km. We detected no herons during our 2023 and 2024 field surveys but opportunistically recorded one individual in February 2023, between 38 Mile and Firmbase, and two near Bor Nala between November 2023 andMarch 2024 (Fig. 2g,h). The earliest surveys of the white-bellied heron (in 2005
and 2006) along the entire stretch of the Noa-Dihing River reported all five sightings west of 40 Mile (Maheswaran,
PLATE 1 A white-bellied heron Ardea insignis photographed in November 2023 along the Noa-Dihing River in Namdapha Tiger Reserve, outside of our fixed line transects. Photo: Rohan K. Menzies.
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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