Why do Cormorants perch on rocks or logs with their wings outspread?

It's called sunning. Cormorants do indeed perch on rocks or logs with their wings spread out, and they do so to dry off their wings. While they may look ridiculous doing so, it's crucial to their health and survival.

Cormorants are seabirds, so their lives revolve around fishing and diving. However, feathers aren't meant for constant submersion. Though cormorant feathers themselves are waterproof, their under feathers get soaked during diving. In order to continue doing what they do best—catching fish—cormorants need to spread their wings out to dry. In fact, since they dive so frequently, they must sun their wings many times throughout the day.