The American Redstart is a sparrow-sized warbler that spends the summer breeding season in most of Canada (except prairies) and most of the US east of the Mississippi River. The exceptions are the Gulf Coast, Georgia and the coastal plains of the Carolinas. They migrate to Central America, the Caribbean and the northern part of South America for the winter. They feed on insects among the forest canopy and will add small berries and fruits to their diet later in the summer.
The males are mostly black with orange patches on the sides, wings and tail. The belly is white. It looks like I startled the one in the second photo but he was hopping and flitting all over the tree where I spotted him. I caught him in mid hop.
Females have a gray head and olive-brown back. They have yellow patches rather than orange. This female has a black splotch on her breast but it is some sort of pigmentation abnormality. They are normally plain white underneath with a yellow shoulder patch.
They are in constant motion through the trees as they search for their insect prey, something that is typical for warblers.