Never had an issue with birds. Did have a seagull poop as he flew over me and hit the stem at the handlebars - perfectly. I don't think it was an accident but I also don't think it was malicious.
Seagulls are birds that like to have fun. I watched a gull dive vertically in a Pacific storm in an updraft off the end of our building. Every break I would go out and look. He kept diving non-stop for 4+ hours. Like a 200 mile mountain descent. He'd found gold.
Took a friend out to see Seal Rocks at the Golden Gate, again in a Pacific storm. 4 gulls were flying slowly and low upwind over the ocean waves, basically staying put. Every once in a while, one would fly up into the full wind, get shot 50' into the air and blown back. Dive back to the ocean 1/2 mile downwind and do the long, slow, hard flight back to his friends. A few minutes later, another would go for the ride.
So I think that gull that hit my bike was just doing target practice. What I don't know was whether that was a bullseye or he was aiming for my helmet.
Ben