A Chestnut-backed Chickadee brings food to the babies and leaves with a fecal sac. Birds typically carry fecal sacs a distance away from nest boxes in order to keep predators from locating their nests.
Check out the beautiful Chestnut-backed Chickadee nests and eggs in the Habitat Section.
You can read more about the Chestnut-backed Chickadee in the Backyard Birds Section.