Do birds tack?

[jack]

This came up the other day and I realised I didn't know. Do birds tack into the wind as boats do? I assumed not because:

* I couldn't see why it would help. A boat tacks because a keel at an angle into the wind can grip the water and have the wind push it sideways, but into the wind. A bird doesn't. If the wind were completely steady the bird would be just like in still air but being translated. I think if a bird wants to go into the wind it's going to have to flap.
* That's not how I've seen birds. They wheel about, but generally when flocking, I assume to coordinate and to evade predators; they don't seem to zigzag.
* No-one ever said they do and I couldn't find any citation

But I thought I should check. Do you know?

Comments

[simont]

Not sure I'm convinced about tacking with a mirror. How does that work? I can see that by angling your sail you could arrange to be propelled at up to 90° to the solar wind, but I can't see a way to actually head into it.

This applies to tacking into gravity, too; I don't think it really qualifies as proper tacking unless you can use it to go wherever you want, which has to include the ability to head for a destination further into the wind than you currently are.

[cartesiandaemon.livejournal.com]

I think you're right, it's not really tacking unless you have a keel (and can use it to go into the wind), and this isn't.

But you can go inwards; kill sideways momentum with an angled mirror, and rely on gravity to go inwards.

(I wonder if there's a transformation of space in which solar wind and gravity can be considered like air and water... :))

[simont]

Not convinced by that technique for going inwards: it only works if you haven't already achieved escape velocity!

[cartesiandaemon.livejournal.com]

Can you achieve escape velocity?

If you have it, you're right, you can't come back without going all the way to another star, which would be a good point to decide if you want to do before you start, but I admit is a limitation in the technique :)