Spotted Mystery

A storm-toppled tree in the Ravine in Prospect Park made a natural bridge for squirrels and chipmunks before it was sliced up. The horizontal trunk was also being used for a plucking station, as these remains attest. The main predators of birds in the park include other birds, raccoons (but mostly of nestlings), and cats. These are contour feathers, which cover the underside of a bird, especially the breast, where most of the muscle (and hence meat) is on a bird.

The otherwise estimable Feather Atlas only covers flight feathers. Bird Tracks & Sign by Mark Elbroach does include contour feathers, but only for a limited number of species. Birds with spotty breasts include several thrushes, Ovenbird, and Northern flicker.
Any ideas?