I saw a large california gull eating a 16" fish... not sure if it was already dead though, i suspect it was. I don't think waterfowl scare fish. However, other birds definitely do. For example: eagles, ospreys, herons, pelicans. However, herons are very good an not getting noticed. Btw, there is a very large heronry just across the boat ramp at policemans with at least a dozen "live" nests.
An interesting story was the time last summer I was fishing fallen timber. I had snuck up on nice brown sipping PMD's, just as I was preparing to make my first cast it all went to hell. I was midstream just outside of a beaver hole, and out came the beaver. To mine and the beaver's surprise he surfaced about 4 feet from me and WHACK!!! He did the tail think and spooked the brown that was about 5 meters upstream. The water was clear enough I saw him bolt to god knows where.
That being said, I spend all last summer fishing next to a beaver's house on the bow river. He would swim right past me within 2 meters and not pay any mind, and the fish didn't pay any mind either. Of course, this beaver never did a tail whack.