Evaluation of nest habitat, site preferences and architecture of the critically endangered White-bellied Heron Ardea insignis in Bhutan

Abstract

SummaryThis research evaluated the nesting habitat, nest-site preferences, and nest architecture of the critically endangered White-bellied Heron Ardea insignis in Bhutan. There are fewer than 60 wild birds left in the world, distributed in Bhutan, India, and Myanmar with fewer than five active breeding pairs in Bhutan. From 2003 to 2018, 20 successful and two unsuccessful nests were located from which at least 76 juveniles were expected to have fledged. The population in Bhutan has remained at 22–30 individuals for the last decade. Site-specific data were collected from 22 nests, and additional vegetation and environmental data were collected from 14 nests and random sites. We used 20-m diameter circular plots to evaluate the site preferences. Ground vegetation, litter and rock cover were evaluated using four 1-m2 quadrats in both nest and random sites. Nesting habitat was analysed to compare characteristics of nesting sites to random sites. Our results suggest that the White-bellied Heron builds a simple platform nest within average distance of 74 m from water bodies on the tallest isolated trees at an average height of 18.3 m on an elevated site with a clear overview of surroundings and are sensitive to even slight disturbance. Our results also suggest that the bird has a preference for an east-facing aspect at an average slope of approximately 40° between the altitudes of 400–1,450 m. Our observations also suggest that the bird has abandoned all nesting sites used prior to 2015, and the frequency of nest re-use has decreased. Protecting each nest site from hazards, avoiding disturbance, maintaining safe feeding habitats and flight routes are essential to ensure continued breeding in current sites and survival of this population. Further research to better understand the habitat requirements for the White-bellied Heron is vital.