Dawn bat (Eonycteris spelaea) live in large roosts in limestone hill caves. One of the largest fruit bats in mainland Southeast Asia, dawn bats pollinate many species of fruit trees, including regional favourites durian and petai. (Photo: Juliana Senawi)

Dawn Bat (Eonycteris spelaea)

Species: Eonycteris spelaea (Mammalia : Chiroptera)

Known Range: Southeast Asia

Size: (Adult) 40-70 millimeter, length of a forearm

Interviewed: Zubaid Akbar Mukhtar Ahmad, bat scientist (zubaid.akbar[at]gmail.com)

(Photo: Eonycteris spelaea by Juliana Senawi)

“DO YOU like durians? Do you like petai?” These are the questions Zubaid asks when he’s trying to win some supporters for bats.

It turns out some bats, like the dawn bat, do a great job ferrying pollen among durian (Durio) flowers and petai (Parkia) flowers. Without these bats, there would be no pollination, no durians or petai.

“And some people cannot live without durians,” says Zubaid, chuckling.

Zubaid shares his thoughts on bats and how dawn bats affect durian fruits in Perak.

In mainland Southeast Asia, the dawn bat is one of three common nectarivorous bat species—they drink nectar from flowers.

All nectarivorous bats sport similar faces: a long muzzle that opens to allow a long tongue to reach into flowers and slurp nectar. They search for flowering trees in forests, orchards and house gardens. 

They can also fly far for food.

In a 1974 study, dawn bats were found to have fed on mangrove tree flowers, and the nearest known mangroves were almost 40 kilometers away. Recent researchers in southern Thailand had fitted dawn bats with radio-collars and found them flying up to 18 kilometers away. 

And when dawn bats congregate in high numbers, they must fly further to look for food, says Zubaid. “They have to spread out.”

As a dawn bat drinks from a flower, pollen sticks to its fur, and the bat carries the pollen to the next flower it visits. By transferring pollen between flowers, dawn bats help pollinate them. 

As for what types of flowers they prefer, dawn bats aren’t too picky: they visit flowers of at least 31 plant species in Malaysia and 15 in southern Thailand. This includes durian, petai, banana (Musa), and mangrove trees (e.g., Sonneratia). 

Pollen on a bat’s fur or in its faeces shows us what flowers it has visited, says Zubaid. 

Zubaid describes how he and his students check what bats ate for dinner.

Dawn bats live in caves, often closer to the entrance. They also make the most noise, along with the fruit bats. In contrast, the insect-eating bats are near silent and roost deeper in caves. At dusk, dawn bats stream out of caves to feed, returning to roost before dawn.

Once the bats have fed, they return to rest in caves. Hanging off the ceiling and walls, they drop their faeces, or guano, to the ground below. Guano fills pits and piles into mounds, sometimes several meters high.

 For many cave residents, guano is a rich, if not the only, source of nutrients and energy brought from the outside world into the cave.

Dawn bats roost in large colonies of up to tens of thousands (as documented in undisturbed caves in southern Thailand). Imagine the amount of guano dropping from the ceiling!

While dawn bats can roost under buildings or inside large drains, they thrive best in undisturbed caves in limestone hills. But such caves are often disturbed or destroyed by quarries, temples and tourism, says Zubaid. And shrinking forests means less food for dawn bats.

So how can these bats be conserved? Give them places to live and feed, says Zubaid.

What bats need, according to Zubaid.

So, the next time you enjoy durians or petai, think of how you can help the dawn bats that make these delights possible.

Further Reading

M.N. Zalipah et al. 2016. The potential significance of nectar‐feeding bats as pollinators in mangrove habitats of Peninsular Malaysia. Biotropica 48: 425-428. 

P.R. Acharya et al. 2015. Home-range and foraging areas of the dawn bat Eonycteris spelaea in agricultural areas of Thailand. Acta Chiropterologica 17: 307-319. 

S. Bumrungsri et al. 2013. The dawn bat, Eonycteris spelaea (Chiroptera: Pteropodidae) feeds mainly on pollen of economically important food plants in Thailand. Acta Chiropterologica 15: 95-104. 

EDITS: (2019/Nov/12) Removed an erroneous description of the dawn bat as the largest of three common nectarivorous bats in Southeast Asia.