This mind-bending image was taken by @Vincent TC (https://www.facebook.com/VincentTC1971) in the Netherlands a couple of weeks back. I was in two minds about how to present the photo - it was tempting to put it upside down! (Look at the bottom,,,)
Vincent was out birding with his camera in bad weather (actually, because of the bad weather!). He got some shots of a Sea-Eagle and a Spoonbill (both different to the species we get here in Australia, of course), but this goose (I think it's a Greylag) landing in very strong wind caused a bit of a stir on Facebook.
Consider the following. A bird is flying and suddenly decides to land, effectively dropping vertically to the ground. This might be due to very strong wind, or if there are raptors (or shooters) around. The bird can’t simply dive to the ground, as this would mean it would gain a large amount of speed. Pulling out of a dive like this before hitting the ground would place huge strain on the bird’s wings.
The bird banks quickly and violently left and right, sometimes actually turning upside-down – as you can see from Vincent’s photo. This spills air from the bird’s wings both left and right, producing a lot of drag and effectively stalling the bird. With the sudden loss of lift, the bird drops vertically, falling like a leaf.
This is normal (if uncommon) behaviour for geese (and some other species including the Black-tailed Godwit), and is called "whiffling".
Glider pilots can carry out a similar move prior to landing, if they have too much speed. Rather than banking right and left, they can “porpoise” up and down. This sheds speed so the glider doesn’t overshoot the runway.
You can also see that all throughout this manoeuvre, the bird’s head remains horizontal so it’s not disoriented. I get a pain in my neck just looking at it.
A few flaps just before it hits the ground and the bird has a soft landing – one in which the bird regains its dignity.
Congratulations on a fantastic photo, Vincent!