Take a deep breath. There is a very good chance that your BP is going to be just fine. From your description, it doesn't sound like he got too much of it. Chances are very good that it will pass through his system. In the wild they don't always have a clean surface to eat off of, and will pick up foreign objects while eating. Keep an eye on him, and remember it may take some time for the mulch to work through his system.
What is his current weight?