It is hard to tell from the photo but I agree it looks like what you're
describing, Wilson. Rat, corn or what I just call a common black snake
here in Southern SC. They aren't venomous. They can get quite long and
of course they can climb steps. They can even climb trees.
Example: Bringing this back to birds, some years ago there was a mated
pair of cardinals nesting in the pyracantha "tree" growing next to my
garage. I could see the tree through the large dining room picture window.
One day I heard a huge commotion. Looked out and the cardinals were
going crazy, diving at something. There was a black snake/corn/rat
snake climbing up the pyracatha to where they had a newborn in the nest.
Those birds managed to scare it off the first time. But the snake was
persistent. It came back. This time nothing they could do would stop
it. I witnessed the snake come back down with the baby, head first in
it's mouth, no doubt neck snapped and already dead. The snake went
underneath the cement foundation of my house. It was quite distressing
to see. But that's nature.
The parents were extremely distraught. The poor birds kept pip-pipping,
calling to each other, flying a short distance away, coming back to the
next. After about three hours they abandoned the nest.
All this to say, of course snakes can climb. :) It will likely be
nesting somewhere near those brick steps, too. Cool and dark.
Jill