hey,
I think this is an animation problem, so I posted here, If it is wrong, please move the topic 
http://pasteall.org/blend/index.php?id=52454
Now, my little bird is in the walking animation and I pasted a particle system with alpha planes. I inserted a collision mesh and enabled hair dynamics. The feathers move during animation, but now the problem:
A few of them start to grow during the movement and they grow and grow and grow. Not all of them, but a few. I don’t know why, everyone got a solution?
Big Thx @ anyone who can help