Ann, Sorry for the loss. This is a terrible feeling. I'm not sure what predator did this. It could be a raccoon or a cat, or a snake (I don't have much experience with snakes) but it sounds as though it is something that couldn't get into the box at the nestlings. Of course, maybe they had their fill when they ate the parents. It doesn't sound like another species of bird as they have specific ways that they kill and this is not what I have seen. You can post the question on the bluebird forum to see if anyone with more experience can advise you.

I know you want to know what did this, but for your own peace of mind, I would clean the box out and reinstall it on a slick metal pole with a baffle. The idea of the baffle is that it wobbles on the pole so that any predator that jumps up onto it will be tipped off. You can use electrical conduit for the pole. This is easy to pound into the ground and to move if you need to mow (provided no one is nesting in it). Another thing to do is to take some paraffin wax and wax the top of the box and about an inch down the sides inside. You can also do this with vaseline, just be careful to wipe off the excess to avoid having the birds get any on their feathers. This will prevent wasps from nesting in boxes. All of these measures can help to prevent this from happening again.

Good luck.

Here is the web site with directions for making a baffle. They are inexpensive and easy to make.

Here is a link that might be useful: predator baffle

Thank you vonyon for your response. Right now the house is attached to a tree. The pole and baffle sound like a much better arrangement.

Sounds likely it was a cat or a raccoon then. I see so many setups like this. Try not to feel bad. I know how you feel.

I'm so sorry.
The same thing happened to me a few years ago with about 5 bluebird babies. And I had the pole and coon baffle, so it must have been another bird. I've heard house sparrows and maybe house wrens can do this too. :(

Catherine, You can prevent both house sparrows and wrens from getting into boxes. Each has their own type of solution. You are right, the baffle and pole will not prevent this kind of death. If you are interested in providing housing for birds, it is a good idea to visit the bluebird forum. People there can advise you on how to avoid those kinds of problems.

House sparrows can kill an adult bird, but they usually peck the skull starting with the eyes. It is a horrific sight. They usually do this in a confined space where the other bird cannot get away (inside the box). The house wren can remove eggs and very young nestlings. Usually they drop the eggs or nestlings on the ground near the box. The way this has been described, it is likely a bigger animal.

For a lot of information on providing housing for bluebirds (and you can apply most of it to any native bird) see the website below.

Here is a link that might be useful: Sialis

The Sialis site is excellent. From reading there, I do believe a cat killed the bird. I have removed the birdhouse, and when or if I set it up again I will be doing it very differently. Thank you for your help vonyon. And catherinet, thank you for the sympathy.