IN the steamy jungles of Belum-Temenggor, four birdwatchers crouched quietly in mud, their gaze permanently fixed on the growing black speck in the distant sky.

The looming thunderous sound punctuated with deep honks throws the team into action to start counting feverishly.

The elusive plain-pouched hornbills have arrived.

"You hear them before you see them. It really is quite spectacular," Malaysian Nature Society (MNS) birder Lim Kim Chye says.

As part of their annual migration, the birds fly south from Thailand. But what makes this event so special to Lim and birders across the globe is that no one has found any nesting or roosting sites despite the big numbers -- last year's count was 3,000 birds.

"This is definitely one of the untold spectacles which many Malaysians don't know about," he says.

Unlike the famed bats of Mulu caves but just like the plain-pouched, bearded pigs are another one of our jungle's best-kept secrets.

Biologist Wong Siew Te says it is a little-known fact that bearded pigs or babi hutan used to migrate annually.

Bearded pigs would form a big herd of thousands of individuals and roam the forests during the day and night.

"A hunter who saw a migration on the Lahad Datu-Sandakan road in the 1970s said it took about an hour for the one herd to cross the road," Wong says.

During such migration, the furry animals can travel up to 1,000km across mountain ranges and also swim across large rivers. "This was the time that the indigenous people would ambush the pigs in boats and spear them in big numbers."

But these migrations rarely happen now and are restricted to central Borneo.

"The last documented migration in Sabah was more than 20 years ago when the forests were still intact," says Wong.

Perhaps the least known of nature's wonders in Malaysia is the mass flowering of tropical hardwood trees.

Gigantic trees in the rainforests such as keruing and meranti blossom all at once, producing a thick carpet of flowers on the forest floor and filling the air with sweet scents. Viewed from above, the rainforests take on a pale white colour instead of the usual sea of greens.

Aberdeen University reader in tropical ecology Dr David Burslem describes the experience as "amazing".

Although mass flowering and fruiting of forests, known as "masting", happens elsewhere, it is more significant here.

"What is unique is how most of the plants species will participate. Even non-tree species such as orchids and herbs will flower then," says Burslem.

Scientists cannot pinpoint exactly what triggers this but they believe that climate is a big factor.

"A short spell of cool and dry nights during the El Nino would usually prompt the mastings."

Malaysia is due for a massive masting since the last one was 13 years ago.