At this point, we don't know whether he's a baby Norway rat, or a young mouse. More Googling for me. I was out feeding the chickens this morning and noticed him clinging to life on the Polaris hose for the pool. He'd evidently fallen in the pool and was lucky enough to locate the only floating thing available. Wet and cold, we brought him in and Pearl dried him with the low setting of my hairdryer. I was sure he'd be dead within the hour because of his ordeal in the pool. Still alive, 5 hours later. He's eating, grooming himself and leaving tiny little presents for us, so I guess he's going to be okay. Pearl's named him Pico. It means "peak" (as in mountain top) in Spanish. It doesn't really apply, but it's a cute name for a cute guy.
Lucky for him, I like rodents. I'm sure the chickens would have made quick work of him if I'd offered him up for breakfast.