The megabat that's gone forever

The Little Mariana fruit bat was never photographed in the wild, unlike its closest living relative, the Mariana fruit bat (Credit: Getty Images)

Getty Images A close-up of a Mariana fruit bat (Pteropus mariannus) (Credit: Getty Images) — The Little Mariana fruit bat was never photographed in the wild, unlike its closest living relative, the Mariana fruit bat (Credit: Getty Images)

The Little Mariana fruit bat slipped into oblivion before scientists even had the chance to learn about its biology or behaviour.

Even the old people on the island said they hardly ever saw it. The Little Mariana fruit bat, Pteropus tokudae, had long been considered a rarity – the mysterious cousin of a larger bat species also found on the Pacific island of Guam. Like many fruit bats, the Little Mariana species had a small, fox-like face and a brown, furry body, giving rise to its alternative name, the Mariana – or Guam – flying fox.

In the 1960s, during a survey that assessed dozens of bats hunted by local people, just one specimen of the Little Mariana fruit bat turned up. It was a female, shot at Tarague Cliff on Guam’s northern coast. She was lactating and so must have been nursing a young pup, which apparently had flown away after the shooting – almost certainly to die.

The female was only the third Little Mariana fruit bat specimen to be examined by western scientists in recorded history. Previously, two males had been collected by a naturalist in the 1930s. These sparse records reveal that this bat was medium-sized, about 15cm (5.9 inches) long and with a wingspan of over half a metre.

The Little Mariana fruit bat belongs to the "megabat" family – a grouping that contains some of the largest bats in the world. We know hardly anything about this fruit bat's biology – what food it favoured or when it bred, for example. Nor do we know how it interacted with that other, larger bat species on Guam, Pteropus mariannus. The Little Mariana fruit bat is about as obscure a species as you can get and last year the US Fish and Wildlife Service declared it officially extinct, following decades of zero sightings.

"I would definitely recognise it," says Tammy Mildenstein, a bat researcher working with the US military, who says there is a tiny possibility that the Little Mariana fruit bat is still out there, hiding somewhere on Guam. She mentions the Philippine bare-backed fruit bat. There were no sightings of that species between the 1960s and 1990s, so it was declared extinct. But it was rediscovered in 2000.

Guam is a much smaller place, however, than Negros Island in the Philippines, where most Philippine bare-backed fruit bats live. And Guam has been subject to plenty of bat surveys in recent years – including by Mildenstein. The truth is that, if the Little Mariana fruit bat really were still out there, it probably would have turned up by now, says Tigga Kingston at Texas Tech University.

The Little Mariana fruit bat's cousin, the Mariana fruit bat, still inhabits forests in the Mariana Islands today (Credit: Getty Images)

Getty Images The Little Mariana fruit bat's cousin, the Mariana fruit bat, still inhabits forests in the Mariana Islands today (Credit: Getty Images) — The Little Mariana fruit bat's cousin, the Mariana fruit bat, still inhabits forests in the Mariana Islands today (Credit: Getty Images)

One question that lingers is whether the Little Mariana fruit bat actually originated on another island. Perhaps a group of these bats were blown over to Guam during a great storm, suggests Mildenstein – this would potentially explain their rarity on the island.

It’s a "great tragedy" that we have lost this species, says Kingston, for it probably played an important role in plant pollination or seed dispersal, she explains.

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The one thing we can do is learn from its fragile existence. "It’s like the canary [in the coal mine] bat in terms of what can happen to these species," says Kingston, who co-authored a paper on fruit bats last year. Many other species in the same grouping, the Large Old World Fruit Bats (LOWFBs), as they are known, are also facing extinction. And the threats really stack up for bats in this group that live on small islands exposed to tropical cyclones, as these storms are exacerbated by climate change.

Habitat loss, hunting pressures and the effects of extreme weather can all become sharply influential on isolated island bat populations. Often, there is nowhere for affected species to escape. "Being on an island can subject you to extreme, rare events," says Kingston.

Of the 75 large old world fruit bats still around, the majority (71%) are considered threatened, she adds. Unless their fortunes improve, more extinctions within this group could unfold in the coming years.

Mildenstein hopes that won't happen. She and colleagues are working to study the larger Guam bat, the Mariana fruit bat, which is endangered and happens to be the only native mammal left on the island. These bats are occasionally hunted but attitudes among the locals have gradually changed, she says: "There's still a bit of poaching here and there but I think the community’s largely on board. People are respecting that bats need their roosting space undisturbed."

Sadly, it is too late for the lost Little Mariana fruit bat. A tantalising species that will be forever shrouded in mystery.

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