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An Overview of the Citizen Science Project for the Study of the Breeding Status and Population of Oriental Pied Hornbills in Singapore

Authors: Bee Choo Strange and Evan Landy

Three species of hornbill have been recorded in Singapore, the Oriental Pied Hornbill Anthracoceros albirostris, Rhinoceros Hornbill Buceros bicornis (extinct) and Black Hornbill Athracoceros malayanus (recent record). In the 1950s, there was no record of hornbills in Singapore. A small population recorded on the main island of Singapore in the late 1960s to late 1970s were presumed to be escapees. However, in 1994, the Oriental Pied Hornbill (OPH) was found on Pulau Ubin and were believed to be visitors from across the Causeway. The first breeding of the species was observed on Pulau Ubin on 26 April 1997 (Wang L.K. & Hails C.J., 2007 and Lim K.S., 2009).

With assisted nesting i.e. installation of artificial nest boxes by the Singapore Hornbill Project in Pulau Ubin in 2005 along with reintroductions at Istana in 2008, Sungei Buloh Wetland Reserve in 2010 and Pulau Ubin in 2013 to diversify the gene pool, the population has increased significantly throughout Singapore (Ong R.Y., 2018).

In Singapore, the breeding season of the Oriental Pied Hornbill starts from December and ends in March or April. The clutch consists of one to four eggs, but usually only one to three chicks would fledge successfully (Teo, 2012). There are more breeding pairs now and they have spread from Pulau Ubin to the main island of Singapore.
It is with this in mind that this project to study the population status of the Oriental Pied Hornbill was conceptualised by Bee Choo Strange from the Hornbill Research Foundation in late 2021 and is now executed in collaboration with Nature Society (Singapore).
The objectives of the study are:
1. To determine the current breeding status and locations of OPH in Singapore, Pulau Ubin and Sentosa. To record the nest tree species and determine how many pairs are using natural cavities and how many use the artificial nest boxes.
2. Using transect survey methods to determine the estimated population of OPHs in Singapore.
The study period will run from February 2022 to August 2022. 

Breeding Status Study

We are seeking information and pictures of breeding hornbills in Singapore, please submit to 

Pic 1: Picture of Oriental Pied Hornbill male providing nesting sealing material to female.

Transect survey
We based the methodology on both (peer-reviewed) hornbill and general urban bird survey techniques. A 2km-by-2km grid was laid over a landscape map of Singapore. There was a total of 289 grids covering Singapore mainland, the Southern Islands, Pulau Ubin and Pulau Tekong, and some of the offshore areas between. All grids were defined by a habitat type identified by the largest percentage cover of defined land or water within the grid. All offshore grids were excluded from the pool of possible sample grids, as were those over the Western Catchment and other state land or private spaces e.g., grids covering Changi airport and military areas. Heavily industrialized spaces such as shipyards and Jurong Island were also excluded. Once all non-viable grids for surveying were removed, we were left with 113 possible survey grids. These all fell under one of three habitat types: urban (>75% hard landscaping), forest (>75% forest cover) and semi-urban (where the percentage of hard landscaping and green cover was between 25% and 75%). In total there were 22 forest grids, 46 urban and 45 semi-urban. 

Using i-naturalist records of OPH’s in Singapore, together with the observations of various experienced bird surveyors, it is apparent that the hornbills are currently living in various clusters in Singapore, for the most part to the east and south of the Central Catchment Nature Reserves as well as in Sungei Buloh Wetland Reserve, Sentosa Island & Pulau Ubin. 

For the purpose of this study, particularly in breeding season, we focus on the southern and eastern quarters of Singapore to gain a more thorough population estimate of the population of OPH in the areas where they are likely to be present. We then systematically randomize our survey grids across the eastern and southern grids of Singapore, ensuring that a coverage of both urban and semi-urban categories are sampled. We have established 34 transects for the study and 95 people have signed up for the transect surveys. 

Pic 2: Location of Sightings of Oriental Pied Hornbill in Singapore

This study may help us to understand hornbill behaviour in the urban environment and for us to find out if the abundance of OPH in Singapore is viable. How many hornbills should there be in Singapore? Findings of the study will be shared through reports. We will be looking into submitting a paper in a local or international peer-reviewed journal.
We are grateful to Mr. Tony O’Dempsey, a mapping specialist and NSS member who has been helping us to produce the survey maps. Thanks also to Dr. Yong Ding Li/ Nature Society (Singapore), Dr. Rohit Naniwadekar/ Nature Conservation Foundation and Assoc. Prof. Dr. George Gale/ King Mongkut’s University of Technology Thonburi, Thailand who have been advising us about survey methodology and information to collect. 

1. Lim K.S., 2009. The Avifauna of Singapore, Nature Society (Singapore)
2. Ong R.Y., 2018. The Distribution of the Oriental Pied Hornbill in the south central area of Singapore. Final Year Report, National University of Singapore.
3. Poonswad P, Kemp A, Strange M. 2013 Hornbills of the World: A Photographic Guide. Draco Publishing.
4. Teo R. 2012 Special Ecology Feature: Conserving Hornbills in the Urban Environment.  A Centre for Urban Greenery and Ecology Publication City Green #4, 130-135.
5. Wang L.K. & Hails C.J. 2007. An Annotated Checklist of the Birds of Singapore. The Raffles Bulletin of Zoology Supplement No. 15.