A friend called the other day on her cell phone. She just passed a bald eagle sitting on a pole with its wings spread out. It never closed its wings and she wanted to know why it was sitting that way. So many questions I cannot answer, but this one I could.
Birds will sit with their wings outstretched for several reasons: 1)to dry off, 2) to warm up and 3) to cool off. I also once read that if they have a heavy infestation of feather mites or other parasites, birds will expose their open wings to the sun to kill the offending invertebrate with exposure to UV rays. I am not so sure about this last explanation.
Pelicans, vultures and raptors are the birds Leonard and I most often see with extended wings, although less often we see others. The picture of the American white pelican (Pelecanus erythrorhynchos) was taken at Baum Lake (Shasta County CA). The early morning was cold and a little snow is still visible on the ground. There were three pelicans sitting with their wings outstretched. They did not move. Definitely these pelicans were warming themselves.
The vulture (Cathartes aura) was sitting on a fencepost near our house (Lookout CA) following a soft spring rain. Thus I feel it was drying its wings – and perhaps warming itself, although the sun was hiding behind clouds. The vulture looks as though it might be landing or flying off because of the extended tail feathers. I watched this bird for over ten minutes and it never flew. Periodically it would flap its wings a bit, necessitating the involvement of the tail feathers to maintain balance. This movement may help with drying.
A year ago Leonard and I saw an awesome sight at the mouth Redwood Creek. Early in the morning there were about twelve vultures with their wings all outstretched standing in a row on fenceposts surrounding a pasture overlooking the Pacific Ocean. The birds simply sat there watching us in the early morning mist. It was almost surreal.