The fact is birch doesn't stand much of a chance in these conditions. It will snap, as any tree will, but these trees had their roots severed by the winds. I counted at least 20 wind fallers in sheltered areas.
Now I bet your thinking what's the point of me telling you this. Well to be honest it's more a case of a warning to all. If you are in the woods take care and be as safe as you can, today I seen the damage a tree can do, a close friend of mine had his leg pinned after a tree fell on him whilst felling. I would hate to hear that anyone gets killed. Some trees can upend with no notice, with soft ground this can become likely. So please when you are out, be vigilant and stay away from hung up and potential wind fall trees.