Native bees and woodpeckers.
I built several nestings sites for the native bees in our area by drilling different size holes in 4"x4" blocks. I had several hundred holes drilled in the blocks I placed around the yard and at the end of summer I was surprised to see that almost all of the holes had been filled. Then about midwinter I noticed that the filled holes were no longer filled and I knew it was to early for the bees to start hatching. One weekend when I was in the backyard I found out what was going on. Looks like I built a dinner stand for the local woodpecker. It was going from hole to hole pulling out the bee larva. Seems the only way I could keep the bees safe was to wrap chicken wire around the blocks. Seems to be working so far.