For the past two weeks or so, a flock of unfamiliar birds have been descending on a neighbourhood in Yishun at dusk.

These long-tailed feathered creatures are not native to Singapore, but are migratory birds called wagtails. As many as 120 to 150 of them can be seen roosting near the Housing Board blocks in Yishun Street 11. Such a large gathering of wagtails in an urban setting has never been observed in Singapore before.

October is typically the peak of the migratory season for songbirds such as wagtails in Singapore, when birds from as far as Siberia in Russia fly south to escape the harsh winter up north.

They may travel as far south as Sumatra in Indonesia, and usually fly back home around March.

About four species of wagtails can be seen in Yishun - the forest wagtail, eastern yellow wagtail, white wagtail and grey wagtail.

When The Sunday Times visited the site on Friday evening, the birds, which have a melodious call, were spotted near the roofs of the HDB blocks, before they swooped down to roost on some palm trees.

Dr Yong Ding Li of bird conservation group BirdLife said such large gatherings of wagtails have been observed in places such as Langkawi in Malaysia, but this is the first time it has been seen here.

"It could be that they had gathered in other places in Singapore under the cover of darkness, which meant the phenomenon went under-reported, or it could also be that there are more wildlife watchers now," he said.

Independent bird researcher David Tan described the gathering as being "most unusual".

"Wagtails are birds that you usually have to venture inside forests to see," he said. "The fact that they stopped among HDB blocks in Yishun highlights the importance of urban spaces in Singapore for transient species."

Audrey Tan

Correction note: The caption for the first photo was edited to reflect the correct name of the bird.