I find that whenever I wash my car, the local birds use it as target practice! Even though we're 45 miles from the sea, we have a resident group of seagulls, and they are a pain. Noisy too.
In my experience the best removal method is to soak it first. Then put a very damp/wet cloth, or kitchen towel at a push, and keep it damp. Within a few minutes, the matter will have rehydrated and just wipe off easily.
Leaving damp paper towel on a helment visor works well for getting rid of flies too. That said, there are a lot less flies about these days. Not a good sign for the environment.
