The floating blind is a marvelous contraption — it lets you slip unnoticed into the private world of birds. Most keep a sensible distance, politely pretending you’re not there. But swans are another matter. When the cygnets are about, the parents paddle straight up as if to say, “And just what do you think you’re doing here?” At such moments, the 600mm lens feels about four feet too long, and I can't seem to back away fast enough.