SINGAPORE - A barn owl has visited Prime Minister Lee Hsien Loong at the Istana again - the third time an owl was spotted there, with previous sightings in 2015 and 2013.

PM Lee on Saturday (Aug 26) posted a photo online of the bird nestling in the overhang along the exterior of the Istana, with the caption: "#guesswhoo's back?"

PM Lee later posted a closer photo of the owl, and said the Istana "appears to be a regular stopover for owls".

"True to their reputed wisdom, they seem to have learnt not to fly into the Istana building (and then need help from Agri-Food & Veterinary Authority of Singapore and Jurong Bird Park to extricate themselves)," he wrote.

"It is rather curious why they only visit every two years!"

The owl could be the same one that he photographed in previous years. In October 2015, PM Lee posted a photo of a similar owl at his Sri Temasek office.

"The owl came to visit us again today. Maybe he is taking shelter from the haze," he wrote.

He had first posted a photo of the same owl in November 2013.

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In both cases, the AVA and Jurong Bird Park were called in to catch the bird and release it, unharmed, behind Sri Temasek.

Barn owls are native to Singapore, but are elusive and so are not often sighted, Animal Concerns Research and Education Society (Acres) deputy chief executive Anbarasi Boopal told The Straits Times on Saturday.

Barn owls became widespread in Singapore since the 1980s, according to Singapore's Nature Society's Nature Watch magazine.

They roost and nest in abandoned buildings and also make their home in trees, it said.