No, when talking about an owl, you would use "den". The "det" in the beginning of the sentence means "it" or "that" as an unknown entity (you don't know, so you are asking). Once you know it's an owl, you would use "den". So: Er det en ugle? Ja, den er sød. Is it an owl? Yes, it is sweet.
I can't think of a good example in English. Maybe: Is it a boy? Yes, he is sweet. Here you go from "it" to "he". Does that make sense?