Birds that weave and sew

February 8, 2020 • 1:30 pm

Here are a few videos of the amazing behaviors of some birds—birds that sew and birds that weave. After you see these, perhaps you won’t see the term “birdbrain” as pejorative.

Here’s Orthotomus sutorius, the Common Tailorbird (not common in any way), a warbler-like passerine that lives in tropical Asia.  It has a stunning way of building a nest. First it takes a big leaf, pierces it with holes, and then, using plant fiber, sews the edges of the leaf together, making a cradle or cup inside which the real nest is constructed. It’s a way of both protecting and camouflaging the nest.

The first video below was sent to me by Bruce Lyon, who shows it in his ornithology classes at UC Santa Cruz. He was responding to my puzzlement about how this behavior evolved. It’s a certainty that the instructions for building this nest-cradle are genetic, instilled in the bird’s brain by natural selection. But for that to happen, there has to be some beginning behavior that is adaptive, and then that evolved into the complex procedure we see today after a gradual and sequential refinement of that initial behavior. For natural selection to have built this, each step of the evolutionary process had to confer a reproductive advantage on the bird. I couldn’t figure out what the initial step was, for it would have had to lead to piercing the leaf and sewing it together; and how did that evolve? I have no idea.

I suppose the ID morons could use this as an example of “irreducible complexity”, for the behavior doesn’t appear to be adaptive until the complex procedure has already evolved. But I’ve learned enough in my years as an evolutionist to realize that this is a limitation not on nature, but on our imaginations. So many behaviors whose evolution has appeared mystifying have, upon later study, revealed incipient stages that one could envision evolving via natural selection into something more complex. (Darwin talked about this in The Origin when pondering the construction of beehives with hexagonal wax combs.)

Perhaps readers of an ornithological bent can posit how the tailorbird behavior got started. Regardless, what we see now is something amazing.

Here’s a longer video (nearly a half an hour) if you have the patience and want to see the whole process:

Weaverbirds don’t sew but weave, but that’s no less remarkable, for their weaving involves tying knots—good ones. This is easier to envision; as Bruce said, “The knots are easier for me to think about incipient stages — lots of birds wrap strands of vegetation around branches to anchor the strand.”  And it’s the males who build the nest, trying to lure females with their architectural prowess. 

And voilà: we get this (there are three videos; the first emphasizes knot-tying:

Here’s the whole process, starting with the knots and continuing with the weaving.

 

More knots and weaving.

 

 

22 thoughts on “Birds that weave and sew

  1. Does this mean that when my wife asks me to fix a minor item around the house, I have to quit grumbling and thank my lucky stars I don’t have to weave a house from scratch?

  2. That is amazing. Ok, here’s my theory on how it arose. Some person demonstrated it to a bird and it tried its own hand in following seasons. The person could also have monitored its progress, providing a refresher course when necessary. Ok, not very likely but interesting to think about. It’s not impossible.

  3. The weaver bird is amazing. I wonder if poking holes could have started as a way of making a window or peephole of sorts? I’m imagining leaves that were shaped in a way (or maybe a bunch of leaves together) that offered shelter but then obstructed vision, which may have led to the need for a hole. I have no idea, of course, and this is assuming the hole came first but this is really wild.

    If the leaf folding came first, maybe there was a bird that realized they could pull one leaf through another using the hole. Kind of ike when you’re out of paperclips or staples and take to dog-earing a stack of papers, the ripping a little “tab” to keep them together …

    Anyway, this is the coolest thing I’ve seen all day!

  4. Yes, How does the skill and knowledge get passed on? How it was developed in the first place is also the hard question. This kind of ability is not transmitted in humans probably because it is not necessary. We have ability in language and writing to pass the instructions on to others. Our problem is in not reading the instructions before doing.

    The bird cannot create a checklist to past the knowledge on. So it is for you evolution/biology experts to explain. I can only explain why we don’t have it.

    1. It’s in the genes, like many other “instinctive” behaviors, so it’s passed on not culturally, but through DNA. I suppose there could be a small element of learning from others, or from failing yourself.

      1. I am sure you are correct and they may soon be able to show specifically which genes are involved. But it also seems true that this kind of transfer is not seen in humans, maybe for the reasons I mentioned above?

      2. Isn’t it also true that something initially passed on culturally might eventually get support in the genome? I’m not suggesting the learning itself gets passed on but the culturally learned behavior gives some selective advantage favoring those individuals who learn the behavior more quickly or accurately or those with a physical or mental “talent” that enhances the behavior. Given enough time, might many elements of the behavior become instinctive leaving little to be learned?

  5. Thanks for highlighting these remarkably skilled birds.

    I remember once you posted some photos of Steven Pinker’s and one photo was (iirc) a weaver. And his caption went something like: it has a program in its brain instructing it how to weave. I always liked that description.

  6. Astonishing. And, of course their brains are quite tiny, so they are packing a lot of behavior into a neuronal thimble.

  7. A pair of turtle doves nest in the wistaria in our garden every year (and usually, alas, have their fledgelings eaten by Chinese civet cats, who have made themselves at home in Japan in fairly recent years). Their nests look rudimentary things, mere platforms, but I am always amazed when I remove them after the nearly annual tragedy at how stoutly they are made. They are made of thin, flexible twigs (often from the wistaria itself), and they are woven together to create a pretty indestructible structure. They are very hard to pull apart. I imagine the weaver birds’ (and long-tailed tits’) skills arose from what may seem to be more rudimentary structures such as these, and then the question arises as to how some er-rudimentary structure arose…

  8. It seems to me the tailor bird has access to some sticky fibers – plant fibers the video claims – and it would be natural to poke a leaf to get rid of it when it stuck. If you do that at a “nest leaf” eventually it will start to stick together and there you go.

    So maybe it get these plant fibers as part of what it would lay down at a nest anyway.

    Re Eli Siegel’s question about gene products, I would rather think gene regulation, expressing first more of an existing tendency for beak cleansing and later an association with the yearly mating cycle. The fully expressed intent weaving is for the evolutionists to explain. 😀

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