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

[gareth-rees.livejournal.com]

Birds and gliders soar using updrafts, currents of upward-moving air such as thermals. Once you've gained height using an updraft then you use gravity to glide upwind in search of the next updraft. Wikipedia's article on gliding has a nice section on soaring.