I have had occasion to shoot both a pheasant and a woodcock (now no puns), while standing there with my zipper down trying to care of business. I am sure you have had similar experiences.
I did that myself today, basically. I was walking along a gravel road south of Aberdeen. It had cattails on both sides and I assumed there was water under the cattails so there would be no birds. As I reached to see that my cell was on, a rooster flew across the road. As it turned out there was no water and that stretch was loaded with birds.
remember, these birds are getting smarter and smarter every year. when they hear a hunter pissing, they know thats a opporunity to fly off and not get shot.
they have a Rooster survival kit. hunter peeing is a #1 of escaping!
Ruffed Grouse here are about the same way. They wait until you've either got your dignity in your hand TCOB or until you step on them before they fly. When they wait until you step on them and they fly, you nearly wet yourself then too!!
Honestly the reason they do that is cause you stopped walking, they got spooked and took off. Maybe you should stop more often Anyone who hunts waterfowl can tell you about all the times they stepped out to take a leak and here comes the birds. Why, because they saw the motion and it attracted them, same reason a spinning wing decoy works.