Hi there,

This week I thought it would be fun to tell you about a bat mystery that I stumbled across during my PhD. It involves a very special bat called Mystacina. And unlike most bat mysteries, where I either look up the answer or still haven't found out the answer, this is one I was able to solve all by myself, just by paying attention to what I saw.

It's the mystery... of the disappearing bat tail.

As part of my PhD, I did a study on New Zealand short-tailed bats for which we made (grainy) videos of the bats. Some of our videos were of bats in flight, while others were of the bats on the ground. One thing that stood out to me from the videos was that the walking bats seemed to have no tail membrane at all, even though the very same individuals had a prominent tail membrane when they flew. My question was... where did the tail go?

Until humans messed things up, New Zealand had no terrestrial mammals, whatsoever. It did, however, have a few bats. Over evolutionary time, the short-tailed bats (Mystacina) started taking some of the "jobs" (niches) that are occupied by things like mice and shrews in other parts of the world – namely eating insects off the ground. As a result, over evolutionary time, the New Zealand short-tailed bats got very good at walking. But importantly, they never became flightless. They still fly perfectly well, even though they're better on the ground than just about any other bats (except vampire bats). When I did my PhD on walking bats, the bats of New Zealand were an obvious subject for study. (Also, that meant I got to go to New Zealand!)

I ended up visiting New Zealand twice, and it was on the second trip that I collected the grainy videos you saw above. (In my defence, that was the best tech we could get our hands on.) The phenomenon of the disappearing tail jumped out at me right away.

I didn't know how the bats made their tails appear for flight, then disappear for walking, but I could understand why they would want to do that. For bats catching insects in the air, the tail membrane is incredibly useful. But for bats on the ground, it's a bit of a tripping hazard.

Tail membranes are extremely helpful for bats that catch insects out of the air; they can use the tail like a net. You can see that beautifully in the video above. Sometimes the bat reaches down with its mouth to eat the insect right after it catches it, resulting in a dramatic front flip.

Could bats be cooler?

No they could not.

For bats walking on the ground, though, the tail membrane is a pain in the butt... area. When a typical insect-eating bat walks on the ground, the tail drags along, picking up debris, getting injured, and generally making life more difficult for the hobbling bat. 

The vampire bats – another group that walks well on the ground – have done away with the tail membrane altogether. Since they don't catch insects, the fact they have no tail has presented no known drawbacks at all. But Mystacina hasn't gotten rid of its tail; it's just found a way to keep it out of the way when it walks.

The solution to the Mystacina mystery lies with a specialized part of bat anatomy. Bats with tail membranes tend to have a spur sticking out of the heel that supports the tail. It's called the calcar. That spur helps the bat keep the tail membrane open when the bat flies.

Mystacina's trick, I learned, is that when it walks, it folds the calcar up, parallel to the leg bone (tibia). In so doing, it hikes its tail membrane up, like a skirt lifted up to avoid the mud. The two raised calcars, combined with the upward-curved tail, serve to completely move the tail membrane out of the way during locomotion on the ground. And when the bat is in flight, it extends the calcars outward, holding the tail membrane in its fully extended position.

The solution to the mystery of the disappearing tail comes down to a powerful calcar, used in a way unlike any other bat.

Fortunately, though, a different mystery remains... look at the video again, and ask yourself...

where did the wings go? 😊

Last Week's Trivial Answer

Last week's question was "Which Canadian astronaut flew to the International Space Station this week? They launched on Thursday, Oct 1." The correct answer was "Josh Kutryk."

Thanks for reading! -Dan