Rabbits? Their droppings are almost round, dark, and slightly shiny. Though I don't know what they would be doing on the porches unless you have potted plants they like. Are the porches at ground level or raised up? Squirrels will leave droppings, too. How large are the pellets? Are they sort of in a pile or just scattered about? Interesting question.
Sandy

Toads and large lizards, like skinks, have relatively large droppings. Skinks are somewhat territorial so you probably won't find lots appearing overnight.

Maybe bats?

Tree frog droppings are quite large. To me it sounds like that's what you have.

The Milk Dud fairy?

We need some dimensions here...size, texture, shape, etc... there are lots of possibilities. Believe it or not, the caterpillars of some of the giant silk moths can leave a huge pellet, although it is hard to confuse it with anything else due to the shape and texture, which is like a small knobby-covered barrel. Do you have trees that overhang the area? Still, these shouldn't be larger than rat scat....
Frog and toad scat is more like a stretched-out oblong shape, hard to confuse it with anything else. Could be squirrel...what is in this area that would be an attractant to them? Look around, take notes, and get back to us.

Now I am definitely interested. Gee, how depressing...anything coliform in nature and I sit up and take notice??

get a good book and sit on the porch and watch.

whatever it is, why not sweep it up and sprinkle on the garden bed?

PS very funny dirtgirl!