I have discovered a nearby wooded hill where these butterflies, Eastern Comma (Polygonia comma), are common in the afternoons before sunset. They frequently land on trees and let me approach them to take close-up pictures. Now is the best time of the year to photograph them in natural light, because in another week, all the trees will be covered with leaves and it will be difficult to take pictures without resorting to a flash.
I have noticed that these butterflies always land on trees with their heads facing either down or sideways, but never up. This results from the way they approach a tree: they always come from above even when they are landing high above the ground.
I can think of one survival advantage in their preferred position. Since a predatory bird is most likely to come from above, a butterfly facing down or sideways will take off away from the bird, whereas a butterfly facing up will have no choice but to fly up and will be more likely to get caught.
Next time I am on that hill, I have to pay closer attention to the flight directions of these butterflies when they are taking off from trees.