Re ECF Project: 2011-19

Project Title: Research on the post-nesting ecology of White-bellied Sea Eagle Haliaeetus leucogaster in Hong Kong

Applicant: Mr. LAU Wai-man of The Hong Kong Bird Watching Society Ltd

Total Approved Grant: $328,500

Duration: 1/2/2012 to 31/01/2013

Project Status/Remarks: Completed

The project aims to study the ecology of the successful fledgling of White-bellied Sea Eagle (WBSE) and identify the survival rate of the fledgling after leaving the nests and the movement range. With combination of AFCD’s nest location survey and this proposed post-nesting ecology survey, a more comprehensive picture will be formed on the breeding ecology of WBSE in Hong Kong, which will enhance the understanding of the limiting factor on the growth of the population.

Summary of the Findings/Outcomes:
The project aimed to study the breeding ecology of WBSE, with particular attention to the fledging and postfledging stages. Tailored field surveys were conducted to collected field data. The field surveys were conducted in three stages, Stage One was to update the latest breeding status of previous nests; Stage Two was to study the nesting period; and Stage Three was to study the fledging and post-fledging period.

A total of 14 nests were found active in the study, of which two were newly discovered. Nesting period for the Tsang Pang Kok pair was found to be around 75 days, which is comparable to overseas study. The post-fledging survey for the Kat O Yeung Chau pair recorded at least 3 months dependence period of the juvenile. It is thought that the juvenile started to become entirely independent at around 33 weeks old, although they intermittently disappeared from the breeding area since 21 weeks old. Some noticeable behavior, particular the juvenile flight practice, was noted during the course of the survey. It was also noted from the survey record that there is a preference on foraging time. Late afternoon, particularly for the hour between 18:00-19:00, appears as the peak hours of foraging.

The field experience learnt from this project further substantiates the view that WBSE survey, particularly for determining breeding status, is a highly challenging study. The combination of remote and inaccessible nest location and hostile survey condition, mainly due to strong wave at the sea, make the WBSE survey becomes a highly skilful and difficult task. In most cases, the surveyors need to infer the status of the nest by indirect method of observing the behavior of the adults.

It is thought that the WBSE breeding population in Hong Kong almost reach its maximum capacity, as not much suitable breeding habitat are available for them. Further research on WBSE’s adaptation to the coastal development is recommended for better understanding of the threat that the WBSE facing in Hong Kong.