The Pekapeka-tou-poto

Oh, sure, the Western scientific community calls this species the “New Zealand lesser short-tailed bat,” but I think we can all agree that the Māori name is much better, especially since you can then call it a pekapeka for short.

Pekapeka. God, I’m so happy.

Scientific name: Mystacina tuberculata. Sadly this was the only creative commons image of the pekapeka I could find, so I’ll ask you to use your imagination for the rest of the article.

Ok, so what’s there to distinguish the pekapeka from the hundreds and hundreds of other tiny insect-eating bats? Well, for starters, they’re one of only three mammal species native to New Zealand. Second, they spend roughly 30% of their foraging time not flying, but walking on the ground.

If that doesn’t sound impressive to you, you clearly don’t understand how much bats suck at walking. Imagine a seal, right? Sleek and beautiful under the water, pudgy-ground humping wobblers on land. Same deal for the bat, only replace the water with the air.

Essentially a bat. (Photo by Andreas Trepte.)

True, there are a few other bat species that are also good at walking, most notably the common vampire bat, which can not only walk but hop and run. But in terms of phylogeny the vampire bat is like a million light years removed from the pekapeka, which is more closely related to the not-so-great-at-the-walking-thing ghost-faced and mustache bats. And unlike the vampire bat, which uses its walking as a stealth maneuver to sidle up to sleeping hosts and give ’em a lil love bite, the pekapeka doesn’t drink blood.

No, the pekapeka may spend time on the ground for other reasons entirely. Remember, it lives in New Zealand, where there are only two other species of mammals (both bats) and no snakes, which means there are next to no terrestrial predators. New Zealand is also home to a lot of birds… and a lot of flightless birds, like the kiwi.

Could the pekapeka be on its way to being the first species of flightless bat?

Well, not if we drive it to extinction first, but I’m getting ahead of myself here.

The Agony and the Ecstasy of Aotearea

So. New Zealand, or Aotearoa if we’re going to keep using Māori words. Kind of a big, isolated chunk out there in the ocean. I mean technically all landmasses are exactly that, but Aotearoa is a little guy comparatively. It’s been isolated for about 80 million years since it split off of Gondwana, which means it has tons of unique species that evolved from those ancient relatives. It just so happened not to carry any early snakes or mammals with it. Being that mammalian predators and snakes are big on eggs and feathers, the birds that did get carried along probably rejoiced.

Those of you with sharp minds and arcane bat knowledge will notice that bats only evolved around 52 million years ago, marking a 30 million year gap between that and the separation of Aotearoa. Well, you’d be right. The bats that did smuggle themselves over probably ended up there by being blown by strong winds across the ocean. Stranger events have occurred.

Along with our lesser short-tailed pekapeka, there’s also the New Zealand greater short-tailed bat, which is closely related and also partially terrestrial, perhaps even more so than the pekapeka. True to its name, it is the larger species, and may even eat creatures as large as nestling birds- filling that gaping mammalian predator niche. It was presumed extinct until a few sightings occurred just recently.

The third species is the New Zealand long-tailed bat, which is completely not related to the other two (it’s a vesper bat) and probably came over during a separate colonization event much later. It is not known for terrestrial behavior.

These three bat species were doing wonderfully well until humans came along. Of course we all know that story. Aotearoa is a particularly harrowing version of the tale, though, since almost half of all its vertebrate species have gone extinct since humans arrived.

The threat to the terrestrial bats was not the humans directly (though I’m sure the extensive habitat loss didn’t help) but to the mammals, particularly rats, that they brought with them. While pekapekas are some of the most impressive walkers in the bat world, they simply can’t compete with hungry rodents. The New Zealand government, bless them, have been working to eliminate rats from most of the outlying islands, but it may be too late to save the greater short-tailed bat.

The pekapeka is only listed as vulnerable, though, thanks in part to some healthy conservation efforts. And probably also due to the fact that it can and does still fly- though generally only a few feet off the ground, and for short periods of time.

So how does the pekapeka manage that whole walking thing, anyway?

The Pekapeka’s Meaty Thighs

At first glance, the pekapeka is your average little insectivorous bat. It weighs something like 10-20 grams, unless it’s been eating recently, in which case it can pack on up to 6 additional grams. (Bats eat a lot.) It’s got short, broad little wings that stretch about a foot wide.

These wings have a specialized adaptive feature for ground travel: the wingtips can curl and tuck away inside a cartilage sheath under the bat’s elbows to free up the arms. The species also has a very small propatagium (that’s the membrane on top of the arm) to have less-restricted arm movements.

The tail on the pekapeka, as its English name suggests, is short, and extends slightly out of the uropatagium (that’s the membrane between the feet) like a gross naked nubbin.

Here’s that lonely picture again. See the gross nubbin?

Face-wise, the pekapeka’s got a bit of a conical snout that’s somewhere between a mole’s and a pig’s. Here is a link to an alarming close-up of that.

That’s a ground-adapted feature, since the pekapeka spends a good amount of time snuffling about in the leaf litter for insects, where echolocation is a slightly less effective tactic. They can and do use echolocation in the air, but on the ground it’s used mostly for purposes of orientation.

Supposedly the pekapeka also uses its teeth to burrow through dirt and wood, but I’ve only found one scientific report of the behavior from the 70’s, so take that as you will.

Like most bats, the pekapeka balances on its rear feet and the pads under its thumbs when moving on the ground. Unlike most bats, the pekapeka actually has extra “claws,” or at least dermal projections underneath all of its actual claws called basal talons. Twice the claw action. Couldn’t find a picture of these to link to, sadly- they are very small.

Ok, I know you all are chomping at the bit by this point, so let’s talk about those strong, muscular thighs.

To understand the true remarkability of the pekapeka’s thighs, you have to understand what a lot of bat legs look like. For example, here is an image of a member of the pekapeka’s superfamily, Noctilionoidea: a ghost-faced bat.

(Photo by Sergio Ticul Alvarez.)

See those black dried-up spaghetti looking things? Those are the legs. Those are the bat’s puny, useless noodle legs.

Now, this is an old specimen, so some desiccation has occurred. But not terribly much.

The ghost-faced bat, as I stated before, is not so great at walking. In fact, it can barely even crawl on those burnt matches. Its legs have evolved in a manner that rotates them 180 degrees from the normal mammalian orientation. Compare it to this mouse.

You’d get bat legs if you took the mouse’s knee and wrenched it around backwards. Please do not actually do this to a mouse.

Now, in species that actually do spend a bit of time crawling, the rotation is a lot less dramatic: it’s closer to 90 degrees, like in this big brown bat.

(Photo by Matt Reinbold.)

This configuration allows the bat to do something cool and exciting: use its knees! When the big brown bat crawls, it draws up its legs against its sides and drags its belly on the ground in a gait that looks much more reptilian than mammalian.

The majority of all bat species have this configuration, which makes it all the more remarkable that the pekapeka came from a superfamily that usually has the useless-incense-stick leg type.

There is a third leg-orientation type, the most triumphant of all. Bats in this group are the supreme walkers: the vampire bats, the molossids, and of course the pekapeka.

A lucky individual holding a velvety free-tailed bat. (Source.)

Check out the calves and thighs on this gal. She could do some brutal squats. The legs of these fellows are still about 90 degrees off the norm, but their calves are rotated higher and their pelvis has a lot more muscle going for it. Compare to the weedy pelvis of the big brown bat above.

Those are some serious walkin’ legs.

Here’s some footage of the pekapeka actually walking. If you’ve seen the way a vampire bat walks, you’ll notice it looks quite different (and less bouncy). That’s because it is different; remember, these bats evolved their walking independently from each other.

Interestingly enough, because the pekapeka could fly before it could walk, so to speak, it uses its forelegs to provide most of the thrust rather than the hindlegs like most vertebrates. The forelegs, after all, are the stronger set of limbs.

Walk, Walk, Fashion Baby

So what does the pekapeka use all this walkin’ for? Well, I mentioned before that it spends only about 30% of its time hunting for insects on the ground. But it actually also only spends about 30% of the time flying and hunting insects in the air. The rest of the time, it forages for fruit, nectar and pollen. Yep, it’s omnivorous- fairly rare for a bat!

In fact, the pekapeka is actually an important (and possibly the sole) pollinator for an endangered plant called the wood rose (Dactylanthus taylorii). Ironically enough, the plant is also threatened by invasive rat activity.

The pekapeka, predictably, roosts in low places such as hollowed-out trees or old burrows. Females tend to roost in related groups with their offspring while males tend to be solitary. Little is known about their social behavior, though I have seen footage of them purportedly hunting in groups on the forest floor.

Come mating time, pekapekas employ a lek breeding system. This means that males will sing competitively to attract female mates. Females are the sole source of parental care for their single offspring, which is able to fly at around four weeks old.

Here’s footage of a baby pekapeka at the Auckland zoo– unusually, the mother in this case had twins.

Regrettably, not terribly much more is known about the wild behavior of this species.

The Pekapeka: A Precursor to Flightless Bats?

There are no extant species of flightless bats, nor have there ever been any observed in the fossil record. By contrast, there are a whole lot of flightless birds out there, and a whole lot of them live in Aotearoa- 16 different species, in fact.

The kiwi is one of them. Interestingly enough, they are also nocturnal insectivores.

The most basic theory behind why flightlessness tends to evolve in birds- in particular, birds on islands or isolated areas- is that flight is energetically expensive, and if you don’t need it, you shouldn’t use it. In other words, without mammalian predators keeping them in the air, birds may come to ground.

Obviously this doesn’t apply to ALL birds; there are just under 100 different bird species living in Aotearoa, and most of them are flighted.

Bats have a global spread nearly as impressive as that of the birds, and there are certainly island species- so why haven’t any of these become flightless?

Well, for one thing, it’s a lot easier to become a flightless bird than it is to become a flightless bat. I just spent a long time explaining how ridiculous bat legs are for trying to do anything aside from hanging upside down. Flightless birds become bipedal, with vestigial arms. Due to their leg structure, bats don’t have this as an option- they need to become quadrupedal, which is still pretty difficult with those wonky back legs, not to mention how they have to walk on their ankles in the front, eliminating a whole joint from the limb.

It might be more energetically efficient for a bat not to fly when it doesn’t have to, but their bodies have become so flight-specialized that it gets really hard to go back. Even in a place like Aotearoa where predators- all avian- come at you from the sky and not the ground.

So in cases where bats do a lot of walking, it’s because there is a really, really good reward for it. Vampire bats- the theory goes- got to be better crawlers when they started sneaking up on their earliest blood donors, which were probably birds sleeping in trees. The common vampire bat, which feeds on earthbound prey, does much better walking or hopping on the ground up to, say, a cow leg, than swooping down to it.

The combination of no ground predators plus a lot of aerial predators probably did wonders for keeping the pekapeka low to the ground; however, it may not be the whole story.

A recent study examining the skeletons of members of the extinct Icarops genus, which is in the same family as the pekapeka, found that they, too, appeared to have legs adapted for terrestrial walking. But the kicker was that some of the Icarops specimens were found in Australia, not Aotearoa. There were semi-terrestrial bats there about 30 million years ago, and there were mammalian predators present. And these bats were probably the ancestors of the pekapeka.

There are a few theories as to why this would evolve on the mainland. One: the mammalian predators may have been mostly diurnal, negating much of the pressure they would place on diurnal bats.

Two: the bat’s terrestriality may not be a response to lack of predators but rather a more energy-efficient way of feeding, much like the vampire bat’s. The pekapeka’s ability to walk means it has access to much larger, groundbound invertebrates such as worms and crickets, and it also allows it to crawl in and out of large flowers rather than having to hover like other bat pollinators.

Three: the authors of the paper suggested that terrestrial behavior may have evolved as long as 51 million years ago, which is interesting, because the first known bat- Onychonycteris– is 52 million years old, and its limb structure indicates that it was capable of moving quadrupedally quite well. Could walking in the pekapeka simply be an ancestral trait that never had enough selection pressure to go away?

I don’t think any of these could be considered the sole explanation; otherwise we’d be seeing a lot more walking in bats. But I do think that there was sort of a perfect storm around the pekapeka’s evolution that allowed to to evolve (or retain) such unusual, and unbatlike, behavior.

I posed a question at the beginning of the article: with the right environment- like the pekapeka’s- could we eventually see the evolution of flightless bats? And I think the answer to that is sadly probably not, given the evidence around us. But then again, nature is always capable of surprises.

More Videos

New Zealand lesser short-tailed bat videos and images are available at ARKive.

“Meet the locals” – Pekapeka. You can see a woman manipulating a pekapeka in this video.

Life of Mammals. David Attenborough gently talks over a group of pekapeka eviscerating a weta.

Pekapeka pollinating flowers.

Lekking/mating behavior in pekapeka.

Read on: To learn more about the incredible diversity in the bat family, read the introduction to Chiroptera. To learn a bit more about reproductive strategies, try chase-away sexual selection. If you’d like to meet another insect-eater, try the aardwolf. And to learn whether or not bats could regain flight if they lost it, I’ve written about whether traits can evolve twice. Also, in my boob post we learn that bats have nipples in their armpits!

References

Hand, S. J., Weisbecker, V., Beck, R. M., Archer, M., Godthelp, H., Tennyson, A. J., & Worthy, T. H. (2009). Bats that walk: a new evolutionary hypothesis for the terrestrial behaviour of New Zealand’s endemic mystacinids. BMC evolutionary biology, 9(1), 169.

Jones, G., Webb, P. I., Sedgeley, J. A., & O’Donnell, C. F. (2003). Mysterious Mystacina: how the New Zealand short-tailed bat (Mystacina tuberculata) locates insect prey. The Journal of experimental biology, 206(23), 4209-4216.

Jones, K. E., Purvis, A., Maclarnon, A. N. N., BININDA‐EMONDS, O. R., & Simmons, N. B. (2002). A phylogenetic supertree of the bats (Mammalia: Chiroptera). Biological Reviews, 77(2), 223-259.

McCracken, G. F. (2006). Functional and evolutionary ecology of bats. Oxford University Press.

Riskin, D. K., Parsons, S., Schutt, W. A., Carter, G. G., & Hermanson, J. W. (2006). Terrestrial locomotion of the New Zealand short-tailed bat Mystacina tuberculata and the common vampire bat Desmodus rotundus. Journal of Experimental Biology, 209(9), 1725-1736.

Simmons, N. B., Seymour, K. L., Habersetzer, J., & Gunnell, G. F. (2008). Primitive Early Eocene bat from Wyoming and the evolution of flight and echolocation. Nature, 451(7180), 818-821.