From the car park walk round the castle grounds where lots of water encourages Mallard, Coot, Mute Swan, various geese and gulls.
Then follow the track across the open area with Kestrel most likely and Sky Lark, Blackbird with Swallows and House Martins at the appropriate time of year. Buzzard will be seen.
And then the canal where Grey Heron can be seen and a possible Kingfisher. Check the hedgerows for Chaffinch and Yellowhammer. In parts Pied and Yellow Wagtail (in spring and summer) are often around.
Finally across open countryside with woodlands to explore to add to the list.