Yesterday a lone mourning dove came to my urban (NYC) rooftop garden to sunbathe, and, it wasn't an attempt to work on her suntan!
Sunbathing is an option mourning doves use to maintain their feather quality to keep them in top shape for flying. According to WBU in Michigan, "In late summer doves are growing new outer feathers... the heat of the sun might help make it easier for doves to shape their new feathers. And along with easing discomfort associated with molting, the sun may also help dislodge parasites so the bird can preen them off more easily."
ADENMENDUM: The digital versions of Volume One within the Words In Our Beak book series that are mentioned in this entry may only remain available for a limited time, but a hardcover version of Volume One can be found wherever books are sold.
Moreover, Volume Two of the book series is now available! Both volumes one and two are in hardcover format (as seen below) and can be purchased any place where books are sold.
Volume One: ISBN: 9780996378529:
Book Seller Info: http://bit.ly/2AFZDCz