Always provide some sort of exit for animals from a window well. Ill.: www.menards.com, www.homedepot.com & www.stickpng.com, montage: laidbackgardener.com
Last fall I was horrified to find a desiccated toad in my window well. Obviously, it had fallen in at some point over the summer and hadn’t been able to get out.
Not wanting to repeat the experience (toads are one of the gardener’s best friends!), I propped up a plank against the well wall at about a 45-degree angle for use as a toad ladder. You could do the same with a log or build a toad staircase of old bricks in one corner. Just be sure to provide something for them—and for other small animals—to escape!