A few years ago, north Texas was treated to an influx of Red-breasted Nuthatches. It happens every few years. These were from the vast evergreen forests of Canada and the northern U.S. known as the Boreal Forest, a huge forest that's home to over 300 species of birds, including Nuthatches. You can usually identify them climbing headfirst down tree trunks, probing the bark for bugs.
Nobody knows precisely why some species fly to more southern areas for the winter; and why Nuthatches sometimes winter here, versus (for instance) Arkansas. But be prepared for more visits from several “boreal” species this coming fall.