In the photo above, a Mourning Cloak rests on the top of a tomato stake in our garden. These are among the first butterflies to emerge in the spring because they overwinter as adults, unlike the Monarchs that have to fly up from Mexico and the others that overwinter as pupas and need to develop before emerging. The underside of the wings (not shown) is mottled like tree bark; that combined with the irregular edge of the wing helps camouflage them against tree bark. This photo was taken in early summer, but I've seen them as early as mid-April, a full month before the Monarchs arrive. One reason they can survive so early in the year is that they can feed on the sap of trees; maple tree sap, for example, has a high sugar content and begins "running" about the time these guys emerge.
The positioning shown above also reflects the surprising territoriality of butterflies. This one swooped at me when I walked nearby, clearly warning me that I was on his turf. It's now late summer, and today I saw a large male Monarch perched... on this same tomato stake. He was cruising from one end of the garden to the other, back and forth, pursuing females that entered the garden and chasing away other male Monarchs (and other butterflies, including swallowtails and little blues).
It's a curious (but not unpleasant) experience to be attacked by butterflies.
Reposted from 2009 to add this photo of a Mourning Cloak nectaring on milkweed in our garden.
More re this butterfly's coloration and biology at The Mourning Cloak (Nymphalis antiopa)