I use a circular polarizer on the cameras for shots near water, and when shooting white birds in particular. It helps prevent blown highlights on the white feathers, and cuts a lot of the water glare.
I thought the filter I had was O.K, but I picked up a Hoya on Ebay and used it yesterday. I got some of the best shore bird shots I ever have, no more muddy colors and blown highlights. I think the cheap CPL filters are just tinted glass, except they aren't that cheap! The price difference isn't that much and the results are worth the cost.
The White Ibis keep showing up around here, I've never seen so many in the 60+ years I've lived here. That's great, I love White Ibis, they're a fun bird to watch.