Understanding how the environment shapes the physical structure of species is important not only for elucidating the drivers of biodiversity, but also for predicting how species will respond to ongoing global change. Using data from more than 250,000 captures encompassing over 100 bird species from the Monitoring Avian Productivity and Survivorship (MAPS) Program, we assessed how the size and shape of birds varies across the North American continent, and how this has shifted over the past three decades. This work, enabled by the efforts of MAPS banders across North America, will serve as the basis for future exploration of the multitude of factors that drive the size and shape of birds across both space and time.