https://phys.org/news/2025-04-bird-stay-unravel-entanglement-stiff.html
The concept of constructing a self-supporting structure made of rods—without the use of nails, ropes, or glue—dates back to Leonardo da Vinci. In the Codex Atlanticus, da Vinci illustrated a design for a self-supporting bridge across a river, which can be easily demonstrated using toothpicks, matches, or chopsticks. However, this design is fragile—pulling one of the rods or pushing the bridge from below can cause it to collapse.
In contrast, bird nests—which are also self-supporting structures consisting of rigid sticks and twigs—are remarkably stable despite continuous disturbances such as wind, ground vibrations, and the landing or takeoff of birds. What makes bird nests so sturdy?
This was the question at the center of a recent paper from L. Mahadevan and his team at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS). The research is published in the Proceedings of the National Academy of Sciences.
Mahadevan is the Lola England de Valpine Professor of Applied Mathematics, of Organismic and Evolutionary Biology, and of Physics at SEAS and the Faculty of Arts and Sciences at Harvard. The paper was co-authored by Thomas Plumb-Reyes and Hao-Yu Greg Lin.
While entanglement in small, flexible systems, such as polymers, is well understood, less is known about how stiff, macroscale components entangle, especially when they are densely packed.
"When we think about entanglement, we typically think about flexible, individual constituents wrapping around each other, as exemplified in tangled headphone cords or entangling vines," said Mahadevan. "Contrary to this common intuition, stiff and straight rods can also entangle themselves—if they are long or thin enough."
To understand how, the researchers used X-ray tomography—a technique that creates a detailed cross-section of an object—as well as computer simulation and experimentation to peer inside and reconstruct the complex structure of bird nests.
The team collaborated with the Harvard Museum of Comparative Zoology, which provided a real bird's nest made from steel wires.
"Pigeons have been known to nest near construction sites and use scrap metal to make their nests, which worked out for us because X-ray scanning on metals provides a clear image to work with," said Yeonsu Jung, a postdoctoral fellow in applied mathematics at SEAS and first author of the paper.
After imaging and mapping the real birds' nests, the researchers created their own, using steel rods with varying length-to-diameter ratios, or aspect ratios. The research team found that the degree of entanglement within a pile of rods depended on this ratio. If the rods had a low aspect ratio—were too short and too wide—the entanglement would be weak and localized at separate spots. But rods with a high aspect ratio—were longer and thinner—had stronger entanglement throughout the entire structure.
"By looking inside these structures, we could see the percolations of entanglement," said Jung. "For rods with a low aspect ratio, there could be pockets of entanglement, but those would still fall apart and stay unconnected. But for high aspect ratio rods, things are really connected inside and the nest would stay together."
Unlike polymers and other microscopic filaments, the team also found that friction and gravity play a role in keeping these systems entangled as well. The team found that nests built with lower aspect ratio packing could become more entangled when exposed to force—in this case, being bounced up and down.
Journal Reference: https://doi.org/10.1073/pnas.2401868122
(Score: 2, Interesting) by Anonymous Coward on Thursday April 10, @12:23PM
See: https://www.youtube.com/watch?v=4A3Mk-M_9Ns [youtube.com]
You can make stable 3d structures too from toothpicks - based on something similar to the first one in the video you can make a tetrahedron or similar. Figured such stuff out long ago when I was a kid. I'm sure others would have done similar centuries or longer ago.
(Score: 2, Insightful) by Anonymous Coward on Thursday April 10, @12:27PM (2 children)
Not mentioned in tfa, how does this process get started? It's not like the first and second rod (or wire) are going to stick to each other until there are more rods in place.
(Score: 5, Informative) by zocalo on Thursday April 10, @02:11PM (1 child)
A couple of years ago, I got to watch a weaver bird in the process of building a different style of nest in South Africa which, for any that don't know, generally create a nest that is a ball of woven grass with a tube or hole at the bottom as protection from snakes. Some species of weaver build communal nests that are an amalgamation of hundreds of individual apartments, other individual nests. This one was of the latter type, and had decided to build his nest suspended in mid-air between two reed stalks about 15cm apart, which it got started by *knotting* the first strand of grass to one branch by holding it in place with its foot and using its beak to tie the knot, doing the same on the opposite branch, then somehow tying the two ends together while hovering in mid-air (due to the angle I couldn't see bit this clearly, unfortunately). The general process seemed to be hold one end in place and grasp the branch with one foot, use the other foot and beak to wrap the other end around it a few times, then tuck the original end back into the knot and pull it tight.
UNIX? They're not even circumcised! Savages!
(Score: 0) by Anonymous Coward on Thursday April 10, @02:27PM
Cool, thanks!
I was thinking of initializing the metal nest described in tfa,
Based on your comments it seems most likely that the pigeon started as you describe, with forked twigs. Once there was a framework (in wood), then all the metal was added.
(Score: 3, Interesting) by looorg on Thursday April 10, @01:19PM (1 child)
From the once I have seen, even tho a somewhat limited selection, they tend to contain a bit of everything. Twigs and sticks for sure but also all kinds of materials they can find such as insulation materials from houses, feathers, wrappers, papers. I assumed they glued it together with spit and other excrement.
(Score: 2) by istartedi on Thursday April 10, @07:30PM
This was my thinking too. There are a lot of spiders around here. The silk is not only strong but sticky, and I wonder how often the birds not only eat the spiders but steal their webs. They seem to be quite opportunistic. They love to pull apart tarps too. Sometimes you find a bundle of tarp strips and sticks that got blown out of a tree.
Appended to the end of comments you post. Max: 120 chars.
(Score: 5, Funny) by Tork on Thursday April 10, @01:47PM (2 children)
heheheh heh heh. heh heh heheh heh.
🏳️🌈 Proud Ally 🏳️🌈
(Score: 4, Funny) by DannyB on Thursday April 10, @06:19PM (1 child)
Boy scouts are taught that rubbing two stiff straight rods together creates heat, resulting in a fire.
The Centauri traded Earth jump gate technology in exchange for our superior hair mousse formulas.
(Score: 3, Funny) by Gaaark on Thursday April 10, @09:59PM
"Oh, my!" in my Sulu voice.
:)
--- Please remind me if I haven't been civil to you: I'm channeling MDC. I have always been here. ---Gaaark 2.0 --