by Tan Gim Cheong
This article was first published in BirdingASIA 28 (2017).
The write-up here is an expanded version with more figures and acknowledgements.
From 1 October to 16 November 2014 Singapore’s first autumn raptor migration count took place at Tuas South Avenue 16 (1.265ON 103.622OE), near the southwest tip of Singapore island, an area with many grassland plots that generate strong thermals during the day. The project was carried out by volunteer amateur birdwatchers but, due to a shortage of volunteers over the 47-day period, full coverage was unfortunately not achieved – observation times varied from two to eight hours per day while on seven days, no counts were made; overall, an average coverage of five hours per day was achieved. Nonetheless, the count was still useful in providing a baseline indication of the numbers and diversity of raptors that may be expected in Singapore during autumn migration.
A total of 3,667 raptors of 11 migrant species were recorded. Oriental Honey Buzzard Pernis ptilorhyncus (3,189 birds) accounted for 87% of the total. The Japanese Sparrowhawk Accipiter gularis (252 birds) was a distant second, making up 7%, while the remaining 6% comprised small numbers of nine species, including 15 Chinese Sparrowhawk Accipiter soloensis. Those three species were recorded throughout the period. A total of 11 Black Baza Aviceda leuphotes was recorded – one on 30 October, two on 1 November and eight on 12 November; six Peregrine Falcon Falco peregrinus – one each on 4, 6 and 8 October and 1, 5 and 16 November; three Common Kestrel Falco tinnunculus – one each on 1, 8 and 10 November; Booted Eagle Hieraeetus pennatus – singles on 18 and 24 October; Greater Spotted Eagle Clanga clanga – singles on 23 October and 13 November; and Osprey Pandion haliaetus – singles on 10 and 16 November. There was just one Black Kite Milvus migrans on 23 October, and one Common Buzzard Buteo buteo on 30 October. A further 183 raptors were unidentified.
Although Oriental Honey Buzzards were recorded throughout the period, there were two noticeable peaks: between 6-12 October (37% of the total) and between 7-15 November (40% of the total). Flocks of up to 80 birds migrated across the site by ‘kettling’ – circling together – in one thermal and gliding to the next, making this site one of the best places in Singapore to observe migrating raptors (eg. prior to the 2014 count, 745 Oriental Honey Buzzarsd were recorded on a single day, on 9 November 2013; an even higher number, 894, has subsequently been recorded, on 9 November 2015).
A count of 31 Japanese Sparrowhawks on 23 October 2014 was the highest one-day number of this species in Singapore. Most of these migrated singly, but up to three were observed kettling together. Chinese Sparrowhawk was encountered only in ones and twos; the largest group of Black Baza was a flock of eight, the remaining three comprised two together and a single. One notable record was a Northern Boobook Ninox japonica in flight on the afternoon of 1 November 2014 – it had probably been disturbed from its day-time roost.
The highest number of raptors recorded on a single day was 490 birds, on 8 October, with an average of 92 birds a day during the period. Notably, there was one day, 3 October, when no migrant raptors were recorded, even though the weather was fine. Reports of migrating raptors 4 km north of the count site, not seen by our recorders, suggest that migration occurred across a broad front, and some birds were not in visual range of the count site.
The flight path also appeared to have shifted slightly compared with earlier years, when about half of the raptors flew south and the rest flew east-south-east. During the 2014 count, few raptors flew south; most flew east-south-east passing to the north of the observers. A survey of the wider area revealed that there was a new area of reclaimed land in the sea between Singapore and Malaysia, north-north-west of the count site, and birds were using the thermals it generated to cross the Straits of Johor; they passed further north of the count site than in previous years. The count site itself was reclaimed from the sea about 15 years ago, indicating that raptors adapt to the landscape altered by man to take advantage of available thermals.
The peak hours for raptor movement were 12h00-16h00. Singapore is at the tip of continental South-East Asia, beyond which lie the Indonesian islands of the Riau Archipelago. Birds passing the site after 16h00 would find themselves flying over the sea as nightfall approaches, and might not have much time to find a suitable roosting site on the small islands scattered to the south.
The general direction of the flight path was from the north-west (Malaysia), then east-south-east towards Jurong Island (Singapore). By extrapolating the flight path, it would appear that most birds proceed directly to the Riau Islands without stopping in Singapore.
Other migrants recorded during the count were: Oriental Pratincole Glareola maldivarum (327), Pacific Golden Plover Pluvialis fulva (76), Pacific Swift Apus pacificus (25), Blue-tailed Bee-eater Merops philippinus (11), White-shouldered Starling Sturnia sinensis (10), Ashy Bulbul Hemixos flavala (9), Red-rumped Swallow Cecropis daurica (5), Bridled Tern Onychoprion anaethetus (2), Streaked Bulbul Ixos malaccensis (2), Eurasian Curlew Numenius arquata (1), Indian Cuckoo Cuculus micropterus (1) and Schrenck’s Bittern Ixobrychus eurhythmus (1).
Sincere thanks go to all the volunteers who helped with the count: Alan Owyong, Alan Yeo, Alfred Chia, Alvin Yeo, Chong Boon Leong, Con Foley, Danny Lau, David Awcock, Diana Jackson, Doreen Ang, Francis Yap, Frankie Cheong, Frankie Lim, Han Yong Kwong, Horst Flotow, Jacky Soh, Jane & Terry Heppell, John Spencer, Lau Jia Sheng, Laurence Eu, Lawrence Cher, Lee Ee Ling, Lee How Sung, Leslie Fung, Lim Kim Keang, Lim Mui Soon, Low Choon How, Nicholas Tan, Ron Chew, See Toh Yew Wai, Subha & Raghav Narayanswamy, Tan Chee Keon, Tan Kok Hui, Timothy Lim, Wing Chong, Woo Jia Wei and Yap Euhian.