Thanks for the response. I had read about what it is and that script to look for errors previously. In fact, this problem seems to go back at least five years, so it's not really a Mojave problem. Anyway, I couldn't find any posts indicating that anyone had ever run that script, found the problem, and then fixed it.
What I ended up doing was logging out of iCloud and ignoring the offers to save (whatever). I then went to the activity monitor and killed the bird and cloudd(?) processes. I then restarted and logged back into iCloud. I had to restart the photo synch and I unchecked a few processes that I don't use (Home, News). (I had unchecked those previously to no avail.) At first I had the bird process running full bore for maybe an hour, but just as I pulled up your response, my fan slowed and then stopped. I checked and bird was no longer showing amongst he top CPU users. I am holding my breath and hoping that it continues to behave itself.
I've seen a couple of other things posted on the web that worked for some people but not for others. The bottom line is that Apple has a long-standing problem for which they have not yet provided a fix. I just wish they would post some sort of "we are aware of the problem and will advise when a solution has been found" message.