American white pelicans (Pelecanus erythrorhynchos) -- about 50 are visible in this photo (I recommend you click on the photo to see the larger version), with hints of more in the distance. These are enormous birds, with a nine-foot wingspan. Although the heavy orange bills aren't very visible here, their black-edged wings are easy to recognize in the air; the link above has a photo that shows the wings clearly.
While some may think of pelicans as coastal birds, white pelicans breed on freshwater lakes and ponds in the interior of the continent. They eat fish while swimming and do not dive from the air.
It was an inspiring sight to see this flock in the sky, their white bodies and wings glinting in the early morning light.