How a fatal virus sparked Ubin's mouse-deer boom

Wild boar decline due to swine fever reduced competition for food

- Ang Qing Correspondent

When a deadly virus wiped out nearly all of Pulau Ubin's wild boars in 2023, mammal scientist Marcus Chua knew he had to document how the ecosystem would rewrite itself.

He suspected that the sudden collapse of the wild pig population (Sus scrofa) due to African swine fever would be a game changer for the greater mouse-deer (Tragulus napu), one of the world's smallest hooved mammals.

The pint-size mouse-deer, celebrated in Malay folklore for its bravery and cunning wit, was once thought extinct in Singapore until Dr Chua helped rediscover it on the island in 2008, ending an 80-year absence from local records.

The species, with individuals weighing no more than around 4kg, likely competed with wild boars for space as well as food, comprising fallen flora and low hanging vegetation, his research found.

"While predation of mouse-deer by wild pigs has not been recorded, wild pigs are also known to eat deer and their fawns," said Dr Chua, mammal curator at the Lee Kong Chian Natural History Museum at the National University of Singapore (NUS).

"With such competition and predation, there was an urgency to understand the ecological consequence of such a major event."

The results were staggering. In the year after the outbreak, the mouse-deer population quintupled to 293 individuals per sq km between 2019 and 2024.

"It became impossible to avoid seeing a mouse-deer during our surveys," said Dr Chua.

This is the highest known density recorded of mouse-deer anywhere in the world, and at least three times higher than known densities elsewhere.

It effectively makes Pulau Ubin the best place on earth to spot these shy creatures, which are commonly found in forests across Southeast Asia.