bridgman,
Toads and frogs prefer cold, wet, damp places to settle which is why they are often found near swampy areas or around muddy places. They are some Canadian species that move around between water bodies and at least one species i recall that does a migration of sorts, mass crossing of roads. It is hard to say whether they have the intelligence to travel back up a pipe or angled board to get back out of your window well.
I think the PVC window that was suggested would be your best bet for keeping the animals from hopping into the well. I am also thinking about the same as added all season weather protection with the less than stellar quality basement windows. The added bonus is that they also keep out the leaves and garbage that tends to collect in those repositories on windy days.
