Thank you everyone. Seems like a properly built house and dry heat are the answer to comfortable winter living.
I am used to a wood burning stove in England and have had some interesting problems with birds. When we first came to this house there was no cap on the chimney top, just a round open hole, and on warm summer mornings, starlings, sunning themselves on the chimney pot rim, would fall asleep and fall down the chimney. This is quite a tall house so the fall would take some time, making strange fluttering and banging noises, with no obvious source, which would echoe around the house. Once we were used to these noises, there was a set routine. Close all curtains and doors, except the back door and get the cats out of the way, then open the stove door. Suddenly there would be a swish of high speed black across the sitting room as the startled bird shot to the nearest and only bright outdoor light. Quite simple when you know what to do, but the first time there were cats, soot and feathers everywhere!