The most tremendous quacking noise today, from high in a tree on Palace Road. I spent quite some time trying to see what was making it - it wasn't like any kind of bird call I'm familiar with. Eventually, I realised it wasn't coming from a bird. It was coming from a grey squirrel.
There he was, fat and furry on a branch, his whole body heaving as he let out each strange croak. If you'd also like to experience the spring song of the squirrel there is an audio clip here. What I heard was slightly less drawn-out, but no more likely-sounding.