For anyone interested, we went down yesterday. Probably approached the park from the wrong direction (to see the bird life) as we came into it coming from Dolphin Bay. It's much easier to go further south on Petchkasem Road and then turn left (east) at Kui Buri (I think) and the bird watching is only a few kilometers away (we came back that way). There were plenty of signs up in Thai and English for the nature watching lodges.
I'm not sure if we were there at the best time, both of year and day, for bird watching but there's a huge marsh area which is where our feathered friends are. Foreigners had to pay 200 THB to enter this bit, Thais were 40 or 50 THB. There's a road/dirt track that goes north past a couple of observation towers but eventually peters out. The centre has a restaurant that we ate at - decent food, decent prices. It didn't sell beer though!! There are clean toilet facilities and a basic information centre with pictures of all the birds you might see - about 200 species if I remember rightly.
There's also an elevated wooden walkway that goes in a semi circle out into the marshes. Must be around 2km walk in total. Also a number of pagoda type places to rest out of the sun. Unfortunately, about half of the walkway had fallen into disrepair so was closed off but I don't think that made too much difference.
There was plenty of bird life including herons, egrets, swallows and others that I can't remember the names of including some weird looking creatures with red heads, orange legs and blue plumage. They were fun. Very strange calls and not especially good at flying or landing on the water.
All-in-all, it was an enjoyable way to spend a few hours.
We combined our trip on the way back with about at hour at Banyan Golf Course watching the sun go down from Mulligan's Pub with a couple of cold beers.
My friends were impressed with the day out.