"Hummingbirds Are Where Intuition Goes to Die"

November 29, 2017 6:06 PM

A long-held belief about how hummingbirds drink is wrong—and the truth is really weird. The hummingbird tongue is a "fluid trap, not a capillary tube." HTML and PDF of the PNAS journal article. Video.
posted by zarq (27 comments total)

!

This is very cool.
posted by minsies at 6:40 PM on November 29, 2017 [1 favorite]

I tried to do the figure eight wing patterns in front of a mirror but wound up looking like a penguin directing traffic...
posted by jim in austin at 7:18 PM on November 29, 2017 [5 favorites]

Hummingbirds drink nectar using tongues that are so long that, when retracted, they coil up inside the birds’ heads, around their skulls and eyes.

Wait what?
posted by jeather at 7:49 PM on November 29, 2017 [6 favorites]

Yeah, I would also like to see a model of a hummingbird tongue when the beak is closed.
posted by If only I had a penguin... at 7:54 PM on November 29, 2017 [1 favorite]

Your wish is my command. Caution: creepy-awesome!
posted by traveler_ at 8:14 PM on November 29, 2017 [24 favorites]

I shudder to think how it would feel to wrap and unwrap one's tongue around one's skull 15 times a second.
posted by subocoyne at 8:23 PM on November 29, 2017 [4 favorites]

So their wee tongues coil up and stow away kind of like a woodpecker.

All ten kinds of interesting that these amazing little feats of engineering are going on around us every second of the day.
posted by Lizard at 8:52 PM on November 29, 2017 [4 favorites]

When I lived in Pacific Heights in San Francisco I had a neighbor that had a 40 year old hummingbird garden.

I found out through old forums posts when trying to identify a hummingbird that nested outside my window. I thought I recognized the house and Google maps confirmed it.

I left a handwritten calling card with my email address in their mailbox and they respond a couple months later. We never met and I never saw the garden, but we talked about hummingbirds a lot. One thing they mentioned is that there was no way capillary action could explain hummingbird drinking.

I just sent them a link to this.

BTW, I encourage anyone who has a garden or even a windowsill planter to look up local butterfly and/or hummingbird friendly flowers and plant a few.

If you get lucky and a hummingbird starts building a nest close by leave some colored cotton fluff or down feathers near by. They will use it to build and line their nest and you will have an easy to find colorful nest to look at. I learned this from my grandmother, who had many red and pink nests in her garden.
posted by Index Librorum Prohibitorum at 9:00 PM on November 29, 2017 [22 favorites]

I shudder to think how it would feel to wrap and unwrap one's tongue around one's skull 15 times a second.

And now you are all aware of how weirdly your own tongue fits in your mouth. All bunched up against your palate and teeth and covered in spit.

You're welcome.
posted by Index Librorum Prohibitorum at 9:02 PM on November 29, 2017 [7 favorites]

Interesting that they came over the Bering land bridge and down into South America, where they radiated out and became well established.

They obviously couldn't have brought flowers along which had already evolved hidden nectaries that could only be reached by their long tongues, but I guess there could have been butterflies and big moths with long tongues already there, drinking the nectar of and pollinating such flowers as they coevolved with them.
posted by jamjam at 9:33 PM on November 29, 2017

Index, I currently hate you.


This is super crazy awesome wierd though.
posted by AlexiaSky at 10:12 PM on November 29, 2017

I bought a fuchsia plant specifically to lure hummingbirds and it worked. I don't see them on my balcony every day but I see them often and will miss them greatly when I move outside their habitat. Great post!
posted by Bella Donna at 10:16 PM on November 29, 2017

I dunno, man.

Call it a “fluid trap” or whatever you want, but that sure looks like capillary action to me. Capillary action isn’t just fluid in tubes. It’s also fluid in small gaps. The hummingbird tongue seems to work on the same principle as a pen nib, which sucks up ink from an inkwell into a tiny gap via nothing more than the magic of surface tension. The gap only holds so much, so once the nectar is deposited in the stomach, the tongue goes in for another go, and then another, and then a bunch more.

It seems like these biologists’ disbelief maybe just comes down to a fundamental misunderstanding of what they disbelieve?
posted by Sys Rq at 10:44 PM on November 29, 2017 [1 favorite]

Figure 2 in the PDF shows the trapping motion.
posted by Pendragon at 12:23 AM on November 30, 2017 [1 favorite]

The tongue physically changes its profile as it enters and leaves liquid, in a way that greatly increases the amount of liquid extracted. That is *not* capillary action.
posted by bjrubble at 12:28 AM on November 30, 2017 [11 favorites]

Heh, scientists. If any of them had ever bothered to kiss a hummingbird they would have discovered this ages ago.
posted by loquacious at 3:51 AM on November 30, 2017 [7 favorites]

Call it a “fluid trap” or whatever you want, but that sure looks like capillary action to me.

The mechanism is more closely analogous to a hinged squeegee (the sort of floor squeegee that has a handle to squeeze out and release) soaking up water when you pull the handle back. That's a different thing to capillary action, even though it looks kind of similar. Hence the century-plus of confusion.
posted by howfar at 5:44 AM on November 30, 2017 [1 favorite]

Someone point the scientists to this thread so they can read Sys Rq's idle speculation about how their peer-reviewed research is obviously wrong
posted by beerperson at 6:03 AM on November 30, 2017 [8 favorites]

Yeah, they're biologists, so obviously they don't know anything about fluid dynamics. Stick to your stamp collecting and your animal drawings, you soft-scientists, and let the physicists and engineers solve the real problems for you!
posted by biogeo at 8:58 AM on November 30, 2017 [4 favorites]

The actual paper gives a pretty nice background on the discrepencies between the nearly 200-year-old theory that the hummingbird tongue works by capillary action and the weight of observations from the last several decades about how hummingbirds actually feed. This includes some interesting nuggets. For example, the biophysics of the capillary-action model predict that hummingbirds should prefer relatively dilute sugar solutions, because these travel by capillary action more effectively than concentrated solutions, but the opposite has been consistently observed. Additionally, if capillary action were the dominant force, it would get a significant boost from gravity when hummingbirds feed from downward-facing flowers, yet no such effect of flower orientation has been found.

In sum, the weight of evidence seemed to strongly suggest that a mechanical pumping mechanism is involved in the hummingbird tongue. So the authors went looking for it, and sure enough, there it was. Science works!

While the authors are clearly primarily interested in the basic science of how hummingbirds feed, they note that the discovery of just how their tongues actually work suggests some interesting novel engineering solutions for things like microfluidic pumps. As is so often the case, studying biology on its own terms reveals patterns that evolution has stumbled upon which can be useful for human technology.
posted by biogeo at 9:15 AM on November 30, 2017 [13 favorites]

By comparing the rates at which new species have emerged and old species go extinct, McGuire estimated that the number of hummingbird species will probably double in the next few million years.

That was a much needed positive thing for me to learn today!
posted by TedW at 12:00 PM on November 30, 2017 [1 favorite]

Someone point the scientists to this thread so they can read Sys Rq's idle speculation about how their peer-reviewed research is obviously wrong

Yes, because if there’s one takeaway from this story, which supposedly “defies a consensus almost two centuries old,” it’s that skepticism is worthless and scientists are always right.

What is described in the paper is absolutely capillary action, and nothing else. They’ve fleshed out the exact mechanics of it (there are little fibers on the tongue, which also act as capillaries), and that’s certainly a worthwhile endeavour, but that’s all. They haven’t upturned any paradigms or anything. Either the authors do not know what capillary action even is, or they’re deliberately sexing up their research to make headlines.
posted by Sys Rq at 12:00 PM on November 30, 2017 [1 favorite]

Mosquitos would seem to have a very similar problem with blood to the one hummingbirds have with nectar, and though it's hard to tell from the materials I've looked at so far, I think they may have solved it in a surprisingly similar way.

In the diagram on this page, we can see that the labrum, the part that seeks out and pierces a blood vessel after the labium has pierced the skin (check out the slightly disturbing linked video), is a hollow tube with one side cut away. The page claims that the hypopharnyx fits over the open side of the labrum and forms a hollow straw like structure, but I think the hypopharnyx more probably fits into the labrum, and once the labrum pierces a blood vessel, the hypopharnyx separates out in a wavelike motion beginning at the tip of the labrum, causing blood to be sucked into the labrum, and then presses back into the labrum, pumping blood back into the body of the mosquito.

I guess the hypopharnyx could wait until the entire labrum fills with blood before pressing back into the labrum, thereby forming a hollow straw like structure filled with blood, but I have a feeling that moving ripples of hypopharnyx extending up out of the channel form along the length of the labrum, instead.
posted by jamjam at 12:46 PM on November 30, 2017 [2 favorites]

What is described in the paper is absolutely capillary action, and nothing else. They’ve fleshed out the exact mechanics of it (there are little fibers on the tongue, which also act as capillaries), and that’s certainly a worthwhile endeavour, but that’s all.

The only way to draw this conclusion is to fail to read the paper, fail to understand the paper, or fail to understand capillary action. The authors are quite clear as to what their findings are, and it has nothing to do with little fibers on the tongue acting as capillaries. They write:

We found that, contrary to the capillarity models, hummingbird tongue tips dynamically trap nectar by rapidly changing their shape during feeding (Fig. 2 and Movies S1 and S2). High-speed video observations show that an entire tongue transformation cycle occurs in as little as 1/20th of a second (cf. ref. 33). This oscillating transformation is driven by fluid and atmospheric forces acting directly on morphological elements of the tongue tips.

[...]

Our observation of rapid lamellar unfurling rules out the idea that the hummingbird tongue tip acts as a set of static capillary tubes during nectar feeding (18–28, 41). The tongue does not passively draw floral nectar up into the grooves via capillarity when its tips contact the liquid; rather, it is dynamically trapping nectar within the lamellae while the tips leave the fluid. Our work with dead specimens demonstrates that neither the unfurling nor the furling of the lamellae requires any muscular work; the process of nectar trapping results purely from the structural configuration of the tongue tips. We are unaware of any other biological mechanism for fluid trapping that is similarly dynamic, yet requires no energy expenditure to drive the opening and closing of the fluid trap.

In other words, the tongue, which has a cross section near its tip shaped like two c's back-to-back, changes shape as it enters the nectar, pulled open by the surface tension of the nectar itself. This deformation pulls more nectar into the tongue. As the tongue exits the nectar, the two c-shapes curl closed, trapping the nectar inside. This mechanism, involving dynamic changes in the transport surface, is not characteristic of capillary action, which involves no changes in the transport surface. Perhaps you're conflating capillary action with adhesive forces? The authors are pretty clear that adhesive forces are involved in this mechanism, though.

Yes, because if there’s one takeaway from this story, which supposedly “defies a consensus almost two centuries old,” it’s that skepticism is worthless and scientists are always right.

Skepticism rooted in an understanding of what scientists are actually claiming and what methods they used to make the claim is valuable. Knee-jerk skepticism which assumes that scientists are too stupid to understand undergraduate-level topics central to their research, and the peer reviewers and editors of the journal were also too stupid to notice, generally is not so valuable.

Broadly speaking, odds are these scientists are probably wrong. (See for example: Why most published research findings are false.) Scientific knowledge is always provisional, and is constantly evolving with new evidence. The more interesting questions are, if they are wrong, were the methods they used to reach their conclusion sound, but more evidence will produce a different conclusion? How else are the known flaws in the dominant model that their work attempted to address to be resolved? If their methods were unsound, in what way were they flawed? How can future work avoid the same errors? This is what critical engagement with science entails. If you start from the premise "they're probably just stupid or lying," you can't learn anything.
posted by biogeo at 5:00 PM on November 30, 2017 [5 favorites]

The authors are quite clear as to what their findings are, and it has nothing to do with little fibers on the tongue acting as capillaries. They write:

If you’ll forgive me, I’m just not seeing the contradiction you’re trying to point out. Lamellae are little fibers on the tongue. They draw and retain the nectar. They seem do this via capillary action. What the scientists have shown is that it’s not the whole tongue itself going in and being the capillary, but the lamellae on the tongue. That’s what I said.

Their conclusions smack of bias. Like, “It’s not the exact capillary action the old guard said it was, therefore we were right in our assumption that it’s not capillary action at all.” But it is. It’s just a much more interesting capillary action. Isn’t that enough?

If you start from the premise "they're probably just stupid or lying," you can't learn anything.

Why not? These guys did.
posted by Sys Rq at 5:44 PM on November 30, 2017 [1 favorite]

Lamellae are little fibers on the tongue. They draw and retain the nectar. They seem do this via capillary action. What the scientists have shown is that it’s not the whole tongue itself going in and being the capillary, but the lamellae on the tongue.

The lamellae are little membranous sheets that are part of the tongue, which I wouldn't personally characterize as fibers, but that's a quibble. I've tried to explain as clearly as I could what the difference is between the mechanism described here, as have Pendragon, bjrubble, and howfar, as have the scientists themselves. You can see the dynamic shape change of the tongue they describe for yourself in the videos included with their paper; I think Movie S3 shows it especially clearly. I don't think any further explanation will convince you that what they're describing is different than capillary action, so I'll drop this.

Why not? These guys did.

What a weird thing to claim. "These guys" do a pretty thorough job explaining the dominant model first articulated in the 19th century, the quantitative biophysical model published 30 years ago, and the various previous studies which have found discrepancies between the predictions of the biophysical model and observations of hummingbird behavior. They take the scholarship of previous authors seriously in motivating their own work. That's how productive scientific skepticism works.
posted by biogeo at 6:25 PM on November 30, 2017 [3 favorites]

Bizarre and awesome! Also the diagram of the hummingbird tongue curled up in the skull. Excellent find, thanks for sharing, it was my favorite thing today!
posted by lemonade at 6:33 PM on November 30, 2017 [1 favorite]