Sunbathing

Believe it or not, sunbathing is an essential behavior for birds.  Not only do birds spread their feathers and bask in sunlight to warm themselves passively (e.g., vultures) or dry their feathers after swimming (e.g., anhingas and cormorants), but they sunbathe for their health.

This juvenile Downy Woodpecker found a bright sunny spot in the forest to take a sunbath. Juveniles are recognized by their red cap, unlike the adult male which sports just a red spot on the back of its head and the adult female which has no red on its head.

Find a nice sheltered spot, protected from predators and wind, spread out those feathers and expose the skin and oil gland at the base of the tail to the direct rays of the sun.  Sunlight helps convert inactive Vitamin D to its active form in the skin (just like it does in humans), and the excess heat of direct sunlight dislodges feather parasites which are then removed by the bird by preening.

Downy Jr spent many minutes in this posture, alternating with a lot of digging through feathers on the back and sides of its body. Fledglings probably pick up a lot of ectoparasites (on skin and feathers) in their crowded tree nest hole.  

And beyond the general health value of sunlight, it just feels good to sit in the sun and think about what to do next.