I think many birds will gladly eat them while they're smallish. Once they get large, it's probably only the more dedicated insectivores that will go for them. Like cardinals. Here's video of a cardinal eating a similar sized caterpillar that could be a hornworm. https://www.youtube.com/watch?v=ktWIEnqKK34 (Warning: the video is a little gross, as the bird really mangles the caterpillar). I haven't personally seen cardinals in the act of eating a hornworm, but something must be doing so because I only find about 2 a year, but I see the moths in my yard. And cardinals do like to nest in my neighbor's hawthorn bush and use my garden as an insect larder.

LOL! Yes tree frogs are incredibly loud! I had about 5-6 singing to each other yesterday evening in the back yard and I could hardly hear my family talking to me while out on the deck! They are really hard to find too. I have one that retires to a little ledge on the top of my shed every year.....same spot. He's so cute! I love going to sleep with my windows open so I can hear them, but sometimes, I just have to close the window 'cause they are sooooooo loud! They are pretty amazing little creatures. I think they are attracted to my backyard because I have several little water gardens. They deposit their eggs in the water. They are so sensitive to the presence of water, that if I go out to just water a few plants, they start singing! I don't know if they see the water, or just hear or smell it! Ain't nature grand? :)

Barn Swallows for sure. I responded to your other post; once Barn Swallows find a good place to nest, they tend to return. Generally taking down any existing nest will just have them build another. Is that a nest box? If so, you may have better luck removing that....but they probably will just build new.

Yep, colours work out. Today I had the male show up too. Both birds are walking very diligently through my flower bed in search of seeds. They make quite a different sound when startled.