The smell of ripe figs draws several small, greyish-brown dayak fruit bats away from the limestone cave where they’ve been roosting. The bats flit and flutter through the limbs, seeking out the ideal pieces of fruit, while maintaining a constant stream of chatter with one another. The bats select the piece of fruit they want and fly off with it to consume it in a safer location. When they’re done, they drop seeds that are too big to swallow or defecate the seeds. Experts report that the seeds the species distribute throughout the forest have an extremely high germination rate.
If you’re lucky, you’ll get an opportunity to spend a little time exploring the old growth areas of Malaysia’s rainforests. If you’re incredibly lucky, you just might catch a glimpse of the rare dayak fruit bat (Dyacopterus spadiceus) that calls those parts of the forest home.
This is a small fruit bat, weighing in at under 150 grams. The tiny body is covered with short, soft grey fur. Its long tail adds an additional 10-20% of length to its body. Its most distinguishing feature is that its head appears too wide for its petite body.
The bat’s primary function is eating native figs and distributing the seeds throughout the forest. When they’re unable to find any figs, the bats will switch to other types of native fruit and will even chew on leaves.
Until recently, one of the dayak bat’s most unique features was that experts believe it’s one of just a handful of bat species that’s monogamous. This was enough to catch the interest of researchers, but they never imagined just how unique dayak males really are.
After mist-netting several bats, they were surprised to discover that one of the male bats had noticeably enlarged nipples. For a moment, the researchers thought they’d made a mistake and actually captured a female, but a quick check showed that they’d been right the first time. The bat was male. When they squeezed the tiny nipple, the researchers were once again shocked when the bat produced a few droplets of milk.
It was all the inspiration needed to launch a detailed investigation of the male dayak bat’s anatomy and physiology.
The investigation revealed that, for some reason, the males developed working mammary glands as well as additional physiological requirements they needed to produce milk. A comparison of the male and female Dayak bat shows that the males are only able to produce about 10% of the milk that their female partners produce while caring for their young. The nipples and mammary glands are also significantly smaller.
This is the first case of male lactation occurring in wild mammals.
There are two theories as to why the male dayak fruit bats produce milk. The first is that the males are believed to help the females raise their offspring. It’s possible that the ability to produce milk is nature’s way of ensuring that the young are adequately cared for if something happens to the mother.
It’s possible the bat’s diet plays a role in the unexpected lactation.
In addition to locally grown fruit, the bats have also been observed feeding on leaves that contain phytoestrogens, estrogen-like compounds. It’s possible that by introducing so much estrogen into their system, it triggered lactation. If the leaves are the reason the males lactate, it’s unclear as to whether the bats eat the leaves to encourage lactation.
To date, males have not been observed nursing their young, but since little is known about the roosting/nesting habits or how this species cares for its young, it’s possible that the male does use the milk to nourish the pup while his mate hunts.
Although rarely seen, it’s believed that the dayak fruit bat has quite a large range that includes parts of Thailand, Malaysia, Indonesia, and the Philippines. Though it’s difficult to get a handle on just how large the current dayak fruit bat population is, the IUCN Red List has decided to list them as near threatened, since the species is particularly sensitive to deforestation and human encroachment. The organization predicts that during the next ten years, the dayak fruit bat population will decrease by approximately thirty percent.
-Excerpt from 60 Beautiful Bat Facts