Did bird embryos have gill slits?

I am not sure if this is a correct answer to your question, because i am no expert on fowl, but I am not aware of birds ever having gill slits in there formation. Humans have slits that have been misconstrued to be gill slits but those are there to help with the formation of your neck and ears.

I imagine that the two cases are related, but, like I said, I am no expert on birds.