This is an American woodcock, a species of bird that commonly lives in fields with tall grass or woods with plenty of shrubbery. This guy suffered head trauma after running into a window, which sadly happens a lot with woodcocks right before winter. Their migratory path takes them right through the city of Boston, and they often fail to avoid buildings in their way. He should be fine though, after a few days of medication and rest we will hopefully release him back to his migration.