These birds are Pileated Woodpeckers.
Although the last two photographs are dark, look closely and you can see how the
Pileated braces himself against the tree. You can tell that the bird is a he from
the first picture where the male's red signature cheek-spot is visible.
The first two pictures are best for seeing the bird's coloring
and the last two basically just show-off the bird's posture.
About the photographer and about the
photographs.