I've encountered birds in clouds. I don't believe I've ever had a bird strike while in a cloud, but I've seen them blow by the windscreen very quickly. I used to believe that they wouldn't be encountered in the soup, too...but experience has proven otherwise.
This is a common hangar flying topic, too...do birds fly in clouds. A favorite around the drop zone was whether jumpers ever hit birds on the way down, or bugs, for that matter. I've never run into anyone that's hit a bird on the way down, and while most jumpers I've spoken to insist the odds of striking a bug are very low, I've nailed a few big ones (june bugs) in free fall...anything's possible...which probably includes hitting a bird IMC.