Bird deemed extinct in Singapore if it has not been spotted for 30 years

Previously, a bird was declared extinct on Singapore's national checklist if it had not been seen in the country's wild spaces for 50 years.

This year, the period was shortened to 30 years.

Dr Yong Ding Li from Nature Society (Singapore), which compiles the annual checklist, said a key reason for the change is that the nation's nature areas are relatively well-surveyed compared with other countries that have large tracts of largely inaccessible forests.

Typically, conservationists around the world use 50 years as a guideline for determining if a species has gone extinct. This assumes that people would have searched for the species within this time period.

But Dr Yong said that in Singapore, "observer effort" - a term scientists use to describe eyes on the ground - is high, with many bird watchers and photographers often on the lookout for rare species.

"Because Singapore is so well-surveyed, if people do not find it within 30 years, that species is likely gone," he said.

But he cautioned that such a checklist merely provides a record of birds that have been spotted in an area, much like how a "pokedex" provides a tally for the total number of virtual monsters that a trainer in the popular Pokemon video game comes across.

The checklist does not assign a conservation status, such as whether a species is critically endangered.

This year, there are 407 species on the checklist. Last year, there were 414.

One of the birds declared extinct and removed from the checklist was the black-thighed falconet, as it has not been spotted here since 1990, said Dr Yong.

But a month after the checklist was published in January this year, it was sighted in the Bukit Brown area.

Said Dr Yong: "The falconet was adamant on overturning its extinction ruling. It is very hard, if not impossible, to say something is gone for good unless you have surveyed every nook and cranny."

The bird checklist by the Nature Society (Singapore), or NSS, is verified by a committee that comprises representatives from NSS, the National Parks Board (NParks) and local experts, said Mr Lim Liang Jim, group director of conservation at NParks.

He noted that checklists of sightings submitted by researchers, bird watchers and citizen scientists are useful for understanding the distribution, seasonality and abundance of birds.

"When compiled consistently over a long period of time, the lists can reflect population trends or even the probability of extinction for threatened species," he said.

"The checklist complements the data from our various surveys and monitoring programmes, and can be cross-referenced to shape and guide our conservation efforts," Mr Lim added.

For example, with the data, NParks can prioritise and direct resources to help birds shown to be rare or whose numbers are in decline, by studying their ecology and actively intervening through habitat restoration and other recovery efforts.