What you're looking at here is a screenshot from one of the fifty so-called "Spatio-Temporal Exploratory Model" or "STEM" Maps published over on ebird.org — some of the most advanced models of birds' migratory patterns ever released.
Created in a collaboration between the Cornell lab of Ornithology, Cornell's Institute of Computational Sustainability, and the Nation Audobon Society, these STEM maps depict the day-by-day predictions of species distribution in a year-round animation, allowing researchers to make predictions about unsurveyed areas of the U.S. at specific times throughout the year (click here to see the map in action.)
The screenshot up top is taken from the animation for the Swainson's Hawk, the most migratory hawk in North America. According to the map's creators, these animations often reveals new information about birds' annual migratory cycles.
Take the Swainson's Hawk, for example. See the bright strip of activity in the Central Valley of California? There has been a dramatic influx of hawks in this area in recent years in what scientists hypothesize is a direct result of California's booming agricultural industry. When you watch the animation, it becomes clear that the hawks arrive in California more than a month earlier than those arriving further East, on the Great Plains.
You can read more about these beautiful maps over on ebird.org
[Spotted on NOTCOT]