Singapore’s first White’s Thrush

The White’s Thrush at Singapore Botanic Gardens presented a significant identification challenge. The Records Committee shares its take on the bird.

Sin Yong Chee Keita and Raghav Narayanswamy Discovery In the late morning of 23 November 2023, a photo of a thrush was circulated around Singapore’s birding community that sent chills down the spines of many. A bird new to the nation was found in the Singapore Botanic Gardens (SBG), co-discovered by Ikson Siah, Keison Ma, and possibly other observers. (If you were also one of the initial finders, could you please submit a record to us mentioning so, as we’d really like to credit you properly!). It was first thought to be a Siberian Thrush, but the lack of a pronounced supercilium and dense scalings on the underparts and upperparts soon revealed that it was something else. Those who recognised the bird knew it was some sort of bird from the Scaly Thrush complex, but the photographs available were not sufficient to identify it initially. Many who received the news visited the site to document the bird, but the main question everyone had was whether the bird was a Scaly Thrush or a White’s Thrush. Multiple excellent photographs that were taken thereafter allowed us to assess its identity and status. Below is the Singapore Bird Records Committee’s take on the bird. White's Thrush at Singapore Botanic Gardens The Scaly Thrush complex The distinctive scaled appearance of the bird indicates that it is one of the species from the Scaly Thrush complex (a complex refers to a group of (sub)species that are very similar looking to each other). Multiple similar species are recognised from the complex today including the Sri Lanka Thrush, Amami Thrush, Nilgiri Thrush, White’s Thrush, and Scaly Thrush. These birds all used to be called the Scaly Thrush until recent history. The first two species are endemic to their island ranges while the Nilgiri Thrush resides in the Western Ghats of southwestern India. These birds look distinctly different (by Scaly Thrush standards), and their wild occurrence in Singapore is more or less impossible due to their range and non-dispersive behaviour. The White’s Thrush on the other hand breeds in Russia and East Asia including Japan, and is known to be a long distance migrant to Indochina and the Philippines. It is also a well-established vagrant to Europe, with records as far as Iceland. In contrast, the Scaly Thrush has a wide range from the Himalayas to Indochina and is generally thought to be resident – but more on that later. A separate subspecies of the Scaly Thrush, sometimes spit as the Horsfield’s Thrush, is endemic to Java and Sumatra. The thrushes that could potentially occur in Singapore based on their ranges are the Scaly Thrush and White’s Thrush. There are several subspecies involved in these birds that might make things confusing, and it doesn’t help that these birds are still so poorly understood. Here’s a quick summary based on current knowledge for the two species relevant to us, with the two most relevant taxa bolded. Taxon Range Notes Scaly Thrush Z. dauma dauma Northern Pakistan through Himalayas to northern Indochina Two taxa are sometimes recognised within Z. dauma dauma, dauma in the Himalayas and socia in southern China. These are indicated in the range map below as dauma W and dauma E, respectively. The western population is thought to winter in northern India, and eastern population to Indochina. The eastern population could potentially occur in Singapore. Scaly Thrush Z. dauma horsfieldi Montane regions of Sumatra, Java, Bali, Lombok, Sumbawa Unlikely to occur in Singapore given its highly sedentary nature. Scaly Thrush Z. dauma iriomotensis Iriomote Island Unlikely to occur in Singapore given its highly sedentary nature. White’s Thrush Z. aurea aurea Breeds Siberia through Manchura to Korea, long distance migrant to south China and Indochina Possible to occur in Singapore as a southern overshoot given its highly migratory nature. White’s Thrush Z. aurea toratugumi Far eastern Russia, Sakhalin, to Korea, Japan. Migrates to eastern China and Taiwan. Some records in the Philippines. While this subspecies could be considered, given its more eastern distribution, Z. aurea aurea is probably more likely to occur in Singapore. Additionally differentiating this subspecies from nominate aurea will be nearly impossible from photographs alone. Range map of Scaly Thrush complex, reproduced with permission from Weir (2018). Could the range possibly be useful in suggesting one species or the other? Again, there is little information available. Initially we thought that White’s Thrush would be more likely to occur in Singapore, as it is the only known long-distance migrant in the species complex. All records from central Thailand are listed as White’s, and those with photos appear to be this species (see Identification). But the records in Peninsular Malaysia listed by Wells (2007) that are supported by measurements seem consistent with Scaly instead, and the Malaysian Bird Checklist only includes Scaly Thrush from Peninsular Malaysia and only White’s in Malaysian Borneo...