Migratory Bird Collisions in Singapore

The Black Bittern was exhausted. He had covered hundreds of kilometres during the night. Now the Sun was rising and it was time to find a suitable place to take a breather and find some food. However, everywhere he looked he saw the brightly lit outlines of concrete giants as far as the eye could see. Just then, he saw it. The first rays of sunlight had revealed a giant covered in greenery and, best of all, the unmistakable shimmering outline of a pond in the centre. The bittern changed course and made a beeline for the pond. Breakfast beckoned…

Singapore lies along a major migratory path along the East Asian-Australian Migratory Flyway (EAAF), undoubtedly Asia’s most important migratory flyway. Used by hundreds of millions of migratory birds annually, more than 100 migratory species pass Singapore on their migratory journeys to destinations further south, the most conspicuous being the shorebirds that can be easily observed in our wetland reserves. Less well known to the public are the songbirds, and other migratory landbirds like cuckoos, nightjars and kingfishers. Many of these species migrate at night, and while their journeys are fairly well documented in Europe and North America, species that migrate in eastern Asia remain very poorly known.

The phenomenon of migratory bird collisions is well-studied in North America, where estimates of birds killed range into the high hundreds of millions per annum, with the majority of these collisions occurring in heavily urbanised areas like New York City. According to scientists, these migratory collisions occur for two reasons. Firstly, many migratory birds migrating at night rely on stellar patterns in the sky for navigation, and thus may be misled by artificial lighting from man-made structures, drawing them in and leading to collisions. Secondly, birds are unable to distinguish reflections from real trees and greenery. As a result, birds flying through urban areas that have vegetation may be drawn to the reflections from windows. Either way, avian victims of these collisions are often too severely injured to proceed with their migrations, or otherwise perish.

Although the issue of bird collisions is unfamiliar to many Singaporeans, there have been an increasing number of reports from birdwatchers who were finding dead or injured migratory birds in urban areas beginning from the 1990s. To understand the extent of migratory bird collisions in Singapore, the Bird Group started a long-term (5 year) survey to document these collisions better. Our study aimed to 1) identify bird species that are prone to these collisions, 2) identify the geographical distribution of these collisions, 3) determine which time of the year these collisions are most frequent and 4) identify aspects of the urban landscape that may increase the risks of these collisions.

Our interview form was disseminated widely to the nature community in Singapore through Facebook and other channels. This form was designed to record key details on bird collisions records from the public, and is available online at http://www.tinyurl.com/sgbirdcrash. As the NUS avian genetics lab also receives many birds killed in such collisions, we are also collaborating with David Tan of the lab to compile details of these records.

This report summarises the results of the first year of data collection, which was carried out between September 2014 and April 2015. Migratory birds begin to arrive on our shores in numbers from September, and the vast majority will have left by April, so this period was chosen as collisions were most likely to occur within this timeframe.

A total of 47 incidents involving 18 species were documented between September 2014 and April 2015 (Table 1), of which 33 resulted in fatalities. Pittas (Pittidae) and flycatchers (Muscicapidae) were the most commonly reported victims, with 11 incidents involving two species of pitta and 10 incidents involving four species of flycatcher including the globally threatened Brown-chested Flycatcher (Rhinomyias brunneatus). Kingfishers (Alcedinidae) were also well represented with eight incidents, all of which involved the Oriental Dwarf Kingfisher (Ceyx erithacus). The remaining 18 incidents involved a wide range of families ranging from raptors (Accipitridae) to grasshopper warblers (Locustellidae) although no more than 5 incidents were documented for each of the families involved.

Bird collisions were most frequent during the fall, or autumn migration period between October and November compared to any other period during the migratory season for 2014/15 (Figure 1).

Figure 1: Number of reported migratory bird collisions sorted by month during the 2014/15 migratory season.

The central and western parts of Singapore were found to be hotspots for migratory bird collisions (Figure 2). Of 47 reported collisions, 20 were from the central region, which is characterised by Singapore’s central business district and several residential districts near the southern boundary of the Central Catchment Nature Reserve. A further 13 incidents were reported from the west, which is characterised by heavy industrial land use but also includes a large tract of relatively undisturbed secondary forest at the Western Catchment military training area. These two regions combined accounted for 70% of all reported collisions during the study period.

The preliminary findings from our ongoing study indicate that in Singapore, the bird families most adversely affected by building collisions are pittas (Pittidae), flycatchers (Muscicapidae) and kingfishers (Alcedinidae). These three avian families are predominantly nocturnal migrants, with many nocturnal collisions and captures reported in other parts of the Malay Peninsula (Wells 2007). Consequently, these birds may be especially vulnerable to collisions with lighted structures owing to the multitude of high-rise, intensely lit housing and office blocks which are a feature of Singapore’s skyline and represent a deadly attraction to these birds.

Figure 2: Migratory bird collisions classified by region based on boundaries demarcated on URA’s OneMap.

Our results also indicate that mortality resulting from building collisions was noticeably higher during the fall migration period compared to any other time during the migratory season. This finding was consistent with a recent study in North America (Loss et al. 2014), which suggested that this was due to larger populations of avian migrants in the fall due to the presence of first-time migrants which fledged during the preceding breeding season.

In summary, the preliminary results of this study demonstrate that bird-building collisions are a regular occurrence in Singapore, particularly during the fall migration period between October and November. Certain groups of birds, in particular pittas, flycatchers and kingfishers, appear to be particularly prone to such incidents. Collision incidents are also particularly prevalent along the central and western regions of Singapore.

We also encourage readers to report any bird crash victims they encounter via the online survey form found at the aforementioned address. Your contributions are invaluable in giving us greater insight into the dynamics of migratory bird collisions in Singapore and also assist in the formulation of management actions to mitigate these incidents.

Literature Cited
Loss, S.R., Will, T., Loss, S.S. and Marra, P.P. (2014). Bird-building collisions in the United States: Estimates of annual mortality and species vulnerability. The Condor 116: 8 – 23.
Wells, D.R. (2007). Birds of the Thai-Malay Peninsula. Volume 2. London, UK: Academic Press.

Table 1: The 18 species of avian migrants involved in bird-window collisions between September 2014 and April 2015. Migration period refers to the months of October to November as well as March and April where many birds are passing through Singapore, while wintering period refers to the months between December to February where collisions most likely involve birds which are wintering in Singapore.

Crashed Bird Gallery

Drongo-Cuckoo

Chestnut-winged Cuckoo

Blue-winged Pitta

Black Bittern

 Downloadable Report (Microsoft Word): Link

  
Principal Author: Albert Low
Photo Credit: Lim Kim Chuah