Pallas’s fish eagle in Bangladesh 631
the tree, depending on the suitability of the branches to sup- port the nest. Nests on communication towers (height: 30–42 m, n = 6) were positioned on the top platform. Most (83%) nests were located within 100 m of human settlements (χ2 = 14.8,df = 1,P,0.0001), with a mean dis- tance of 71 ± SD 189 m (range 1–311 m; n = 53). Similarly, human activities such as agriculture were recorded in the vicinity of 96% of all nests (range 1–200 m; n = 53), and 26% of nests were positioned within 500 m of roads. Sixty-two per cent (n = 33) and 49%(n = 26) of nests were within 500 m of rivers (mean distance 1,320 ± SD 2,146 m, n=53) and wetlands (mean distance 801 ± SD 780 m, n = 53), respectively (Table 2). Overall, logistic regressions for effects on the presence of Pallas’s fish eagle nests compared to ran- dom sites 200 m away from the nest indicated a significant effect (r2 = 0.69, F = 69,P,0.001)ofthe nest tree’sheight, circumference at breast height and crown density (Table 3). Permanent wetlands within a 5-km radius (mean area
5.57 ± SD 6.80 km2,n = 53) had a significant positive effect on Pallas’s fish eagle nest habitat selection, compared with random locations at a minimum distance of 5 km from a nest. Other habitat variables such as agricultural lands (mean area 11.9 ± SD 5.33 km2), paddy fields (mean area 54.9 ± SD 8.37 km2), and other land use (mean area 13.5 ± SD 6.28 km2) had weak effects (Table 3).
Aggregated nesting pattern and priority areas
FIG. 3 (a) Distribution of nest locations and permanent wetland areas (including rivers) in 2020, and four clusters, where n indicates number of nests and a the area (ha) of the cluster. (b) Permanent wetland areas in 2010, and locations of Pallas’s fish eagle nests that were lost or abandoned since the early 2000s, based on interview survey results and current nest locations. The distribution of permanent wetland areas in 2010 indicates that many extirpated or relocated nests were in sites with permanent wetland areas.
Nesting habitat
We collected habitat data at the locations of 53 Pallas’s fish eagle nests, of which 47 (88.6%) were in trees. The most commonly used tree species were the red silk cotton tree Bombax ceiba with 14 nests (26.4%) and the rain tree Samanea saman with seven nests (13.2%). An additional 11 tree species were used in smaller numbers (1–4 nests), and six nests (11.3%) were on telecommunication towers (Table 2). The mean circumference at breast height of the nesting trees was 195 ± SD 81 cm (range: 90–450 cm) and the mean height was 13.5 ± SD 4.4 m (range 6.0–21.3 m). Of the 47 nest trees, 46.8% had an open, 42.5% a partially open and 10.6% a partially dense canopy. Nests were posi- tioned either at the top or within 2mof the highest point of
The 53 active Pallas’s fish eagle nests were distributed across a total of 10 subdistricts of Sunamganj and Netrokona dis- tricts in north-east Bangladesh, with the maximum num- ber of nests located in Tahirpur subdistrict (22.6%, n = 12). The eagles tended to nest near each other (β = 1.05, 95% CI = 1.01–1.10; Fig. 3), with 62.3%(n = 33) of nests within 3 km of one or more nests (Supplementary Fig. 1; Clark and Evans test: R = 0.36,P= 0.001; R,1 indicates a non-uniform pattern). The overall mean nest density was 1.2 nests per 100 km2, with four nest clusters (78% of all nests, n = 41); Tanguar Haor cluster (Fig. 3) had the highest nest density (4.8 nests per 100 km2,n = 23), followed by Chhatak cluster (3.7 nests per 100 km2,n = 9).
Discussion Community-based interview surveys
Our findings demonstrate that data obtained through large-scale community-based interviews can be verified by field surveys confirming the presence or absence of the target species (Turvey et al., 2014; Nash et al., 2016). Using this approach, we provide a comprehensive overview of the population and conservation status of Pallas’s fish eagle in north-east Bangladesh, which is the only remaining
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
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