Some predator may have tried to grab the youngster by its tail and pulled the feathers out. Normally, wing and tail feathers would develop simultaneously in young birds, so a fully feathered wing and absence of tail indicates some foul play here.
Woodpecker tails form the third leg of a tripod with their feet to support them on vertical surfaces, as the photo below illustrates. The central tail feathers are pointed and especially stiff, propping the bird up while holding the body away from the tree surface.
Woodpeckers typically spread their tail feathers as they land on a vertical surface, increasing the surface area of that third leg. The central quill (rachis) must be strong enough to function as a support but must also flex and not bend, like a drinking straw would. This is accomplished by increasing the diameter of the central tail feather rachis, filling it with a high density of interlocking keratin proteins surrounded by a rigid keratin shell.
Without its tail support, young RBW will find it difficult to forage for grubs under the tree bark. Perhaps that’s why it has been a constant visitor at the birdseed feeders recently.