By Raghav Narayanswamy and Adrian Silas Tay

If you were birding in 2022, you might have seen the Ruby-cheeked Sunbirds that were frequenting the area near the Aerie Tower at Sungei Buloh. But did you know that during their stay they actually built not one, but two nests during their nearly three-month stay? Together with collaborators from the Sungei Buloh Wetland Reserve team (Shu Fen, David, Fadhli, and Samuel – thank you!), we documented these breeding attempts recently in a Biodiversity Record in Nature in Singapore.

Background

Despite its status in the surrounding region – it is fairly common in various habitats in Johor, for example – the Ruby-cheeked Sunbird has never occurred as a resident in Singapore. It was only first recorded in 2005 at MacRitchie Reservoir. Records since then have been at Pulau Ubin (2018, 2021, and 2022) and Sungei Buloh (2020, 2021, and 2022 – this record). There were gaps of several months between each of these sightings, suggesting the possibility of repeated water crossings from Johor.

Breeding attempts in 2022

The first nest was built between early June and mid-June 2022. On 5 June, a male and female were seen collecting nesting material near Shelter S1. Later that morning, the nearly completed nest was located about 20 metres north of the Aerie Tower, hanging from a fishtail palm frond about 8 metres above the ground. The female was observed sitting in the nest for long periods, possibly incubating eggs, on 11 and 12 June, but by 13 June, the nest appeared abandoned.

But the same day, a partially-constructed second nest was discovered near Observation Screen 1.9, about 300 metres south of the original site. The nest was built in a more concealed location, still on a fishtail palm but not directly over the path. This time, nest-building was observed for a few days, and intense activity continued until around 20 June, but subsequently slowed and stopped entirely by 23 June. After the failed nesting attempts, sporadic sightings, mostly of male birds, were made until July 2022. The last sighting was on 25 July 2022. Despite searches over more than two years, there have been no further records anywhere in Singapore since then.

Outcomes

Both nesting attempts ultimately failed. The first nest was abandoned after the female was observed apparently incubating for two days, suggesting a possible predation event or environmental disturbance. Retrieval of the nest revealed a solidly constructed structure but no eggs. 

The second nesting attempt was faced with another problem – aggression from a pair of Brown-throated Sunbirds nesting just a few metres away. The larger Brown-throated Sunbirds were seen stealing nesting material from the Ruby-cheeked nest and even physically attacking the pair. 

What does it mean?

The failed nesting attempts of the Ruby-cheeked Sunbird in Singapore illustrate the challenges faced by bird species attempting to establish breeding populations in new environments. While some birds, such as the Grey-headed Fish Eagle, have successfully colonized Singapore from the surrounding region, others – like the Ruby-cheeked Sunbird – face competition from established residents. However, the fact that they attempted to nest twice in a short span suggests that Sungei Buloh might provide suitable habitat for breeding. Since dispersal and colonization are fluid processes, future breeding attempts remain a real possibility. Given that similar habitat is available elsewhere in Singapore, particularly in areas with mangroves and coastal forests, continued monitoring may reveal additional nesting attempts in the coming years. Indeed, recent sightings at Chek Jawa, probably of dispersing birds as well, suggest the sightings at Sungei Buloh were not a one-off event.

The Ruby-cheeked Sunbird’s breeding attempts at Sungei Buloh represent another chapter in the ongoing story of bird dispersal in Singapore. A series of Sundaic visitors, including long-staying single birds like the Black-and-red Broadbill at Sungei Buloh and the female Black Hornbill on Pulau Ubin, have turned up in recent years without breeding evidence. The Ruby-cheeked Sunbird appeared and attempted to breed over a comparatively short period of time. Whether or not they will eventually establish a stable breeding population remains to be seen – only time will tell.

Acknowledgments

From the Sungei Buloh Wetland Reserve team, Muhammad Fadhli bin Ahmad, Samuel Ng, David Li, and Yang Shufen co-authored this work and kindly retrieved the first nest for detailed analysis. Hundreds of birdwatchers observed the sunbirds and shared their sightings and photos online – in particular, information from these observers enabled us to track the trajectories of the two nesting attempts: Albert Low, Francis Yap, Kelvin Ng, Raymond Siew, Wee Aik Kiat, Vincent Ng, Yasuko Chow and Ying Loong Chan. Their observations are individually credited in the original Biodiversity Record. Raymond Siew and Vincent Ng contributed excellent photos. 

We are grateful for all these valuable contributions.