I think you have mellow birds where you are. My birds eat the bait out of my Kania traps which are basically straight up and down. Maybe if the whole inside was greased it would deter them.
I have recently had problems with the smaller birds getting at the bait in the squirrelinators. I wish the mesh was a little bit smaller.
So far I have not put any tube traps out, I am saving them to mount them in trees when the squirrels go after the fruit.
My general conclusion on traps vs birds is if you want to be serious about catching squirrels you need to refresh the bait every day. My approach is I have a period when I am refreshing every day, then I take a break for a few weeks, then refresh every day, etc. Maybe a bird feeder would be a good idea, give them something tastier to distract. One day I put out some sunflower seeds along with the PB and those seeds were gone in an instant.