as long as they have fur they shouldn't sunburn (you don't burn on your head, only where your part is). keep them on grass in the shade cuz it's much cooler, and not for very long. you can do the pea-bobbing, or you can even freeze peas right into the ice cube so they have something to play with. red and blue eyes though, are much more sensitive to the sunlight. so if your ratty has red eyes, i'm not even sure if shade is okay for them. it's just so friggin bright out. try in the mornings when the sun isn't so high.