Something is moving.

Who installed the trim?

A local handyman. Is the movement to be expected? I know people recaulk countertops with the changing seasons, is this similar?

Judging from the photo, that looks like snow on a neighbor's roof. My guess is that the wood is moving in response to seasonal changes in relative humidity. Wood is a natural material and such movement is natural, too.

I'd call that a poor install. No telling what material was used either.

Here is a video showing how to keep that from happening. Skip to just before 7:00 if you just want to see the important part.

https://www.youtube.com/watch?v=8-6xuxJv4GU

If you caulk, and the wood then expands, you will see the caulk squeeze out of the joint.

A handyman will often lack the knowledge and resources to do a better job, and homeowners often lack the ability to judge the work being done, or to specify how to do the work.