Breeding Density and Habitat Selection of the Grey-Headed Fish-Eagle in Noakhali District, Bangladesh

Abstract

The Near Threatened Grey-headed Fish-Eagle (GHFE, Ichthyophaga icthyaetus) has undergone a moderately rapid population decline due to habitat degradation. We studied population density and nest-site characteristics of the GHFE at Noakhali, Bangladesh, between November 2015 and January 2016. We used distance sampling along eight line transects to estimate GHFE breeding density. At each nest, we recorded height and crown density of nesting tree, and distances from nearest human settlement, waterbodies with commercial fisheries (hereafter, commercial waterbodies), and waterbodies without commercial fisheries (hereafter, noncommercial waterbodies). We estimated 0.27 (95% CI: 0.15–0.49) GHFE nests or 0.54 individuals per km2. We detected a total of 26 nests, with 85% built on siris (Albizia spp.) trees. All nests were built on the tallest tree within the vicinity of the nesting site, with an average height of 12.5 ± 1.5 m, and on trees with open (69%, n = 18) canopy structure. We found that 76.9% of nests were located within 100 m of human settlements (χ2 = 4.13, df = 1, P= 0.04) and 73.1% were located closer to a commercial waterbody than a to noncommercial waterbody (χ2 = 13.4, df = 1, P= 0.0002). Total area of commercial waterbodies within 500 m of nests was higher than that of noncommercial waterbodies (W= 507, P= 0.001). These results indicate that GHFEs do not require undisturbed or natural waterbodies and can survive well in some human-modified landscapes if adequate food (e.g., commercial fisheries) and tall trees for nesting are available; thus the species may be less vulnerable to environmental changes than previously thought.