BirdOasis said:

Will the heat darken the wood?

Constant exposure to water, heat and the elements will cause changes
in coloration.

What would I use to protect the wood from the water without harming the
birds?

Is this even possible?

Assuming this isn't a cloaked ad...

My concern in making this from wood is the possibility of bacteria and
such living in the cells of the wood. I don't know if this is a
serious concern, but birds drink from AND bath in birdbaths.
Just as with a wooden chopping block, bacteria could build up to
harmful levels if not treated appropriately.

Really good Boat Epoxy would be my first guess as to a finish.

FWIW,

Greg G.