Pele’s hair – Tales from Hawaii: Part 1

Recently I’ve been on an amazing trip to Hawaii. I was planning to write about the observatories there. Then I saw this.

CC-BY Karl Wienand

It’s solidified lava! So… yeah… gotta talk about that!

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Physics and the rules of bird flocks

The season is turning: time for geese, swallows, and all others to relocate. With or without coconuts.

You thought this would be biology’s turf, but physicists cannot resist a cool problem when they see one! Or two…

The V-shape formation

Many large migratory birds (geese, apparently cranes and pelicans) fly in a characteristic V-shape formation. That doesn’t look like the most intuitive way to just go around.


CC-BY Mike Lewinski/Flickr

But there’s a very good reason to do it: save energy. Keeping 5 kilograms of goose up in the air is a lot of work to begin with—let alone fly it non-stop across an ocean. Thanks to the V formation, however, it’s up to 30% less work.

Using fluid dynamics, scientists found out exactly how it works. During flight, the wings waft up off their tip a small current, called upwash, which, as the name suggests,  pushes up—at least if you are in the right place.

Planes, too, create upwash vortices off their wingtips when flying. Credit: wikimedia

Planes, too, create upwash vortices off their wingtips. Credit: wikimedia

To catch it, we just need to stay a little above and slightly off the wingtips of the goose in front of us. Should we stay left or right, though? Easy: whatever those in front did. We’ll keep the whole flock in sight and get the tidiest current. If everyone does so, the group will automatically draw that unmistakable V in the sky.

Anarchy in the flock!

CC-BY-NC Abraham Morales/Flickr

Long, nonstop flights aren’t for everyone, so not all birds need to save energy. Some, like starlings, only care about not becoming someone else’s dinner. For that you don’t need special formations, just stick together.

Recent researches found that flocks stay and move together without a leader directing them. Simulating the movement of birds, physicists found that giving each simple rules to follow—like “don’t crash into other” or “go where your neighbors go”, nothing fancy—created compact, coherently-moving flocks.


The rules, you probably noticed, are really unspecific, they could apply to just about anything. And deliberately so: the scientists couldn’t care less if they were studying flocks of birds, herds of wildebeests, schools of fish, or a bunch of bacteria for that matter. If the rules are the same, so is the result.

That’s the fascinating part of physicists sneaking in different topics: in a chaos of moving parts, they dig up the few little cogs that move the whole machine. And they figure out what the problem has in common with other ones, no matter how apparently different. Physicists are pretty cool.

Cover photo: Le tout, CC-BY-ND Eiimeon, via Flickr. Some rights reserved.