A bit off topic, this, but may be of passing interest.
In a previous life, I worked on the automation of lighthouses around the British Isles. I spent several months (not consecutively!) on the tallest of these, Bishop Rock, which was on the migration route for some bird species. Every morning I used to walk around the gallery outside the lantern, and hurl the unfortunates that had flown into the glass (nav system confused by light?) over the rail.
These birds would invariably descend in a flat spin. There not being a great deal to do on a lighthouse after work, I attempted to improve the flight characteristics of these deceased aviators, to get them to glide. I tried extending their wings by affixing a coathanger - same result.
Then it occurred to me that since birds are all fly-by-wire they don't need a vertical tail surface. So the judicious application of a fairly large cardboard fin, fixed to the tail with some difficulty, improved the flightpath. Still needed some work on pitch control, though.
Bruce