A majority of North American passerines have distributions that focus on either the Eastern forests or Western forests and deserts, and it is a comparative minority that are truly birds of the mid-continent. Clay-colored Sparrow is one of the exceptions. It breeds primarily in the western Great Lakes, south-central Canada, and northern Great Plains. In migration it streams southward to winter in Texas and northern Mexico, with choruses of their buzzy songs signaling a return northward in April.
Although the model misses the fact that this species is a regular winter bird in southwestern Texas, it correctly understands that most of the population leaves the U.S. in winter. The northward surge beginning in March and extending through April and early May is accurate, and indeed these subtle but attractive sparrows can be among the more common migrants through the Great Plains.
Although the model may be a bit generous in predicting significant migration on the West Slope of the Rockies (into Utah, for example) it is interesting to reflect on the subtle ellipse seems to be drawn. The predicted spring route is a bit more eastern (focused on central Kansas) than the fall movement, which seems to shift a bit more towards western Kansas and eastern Colorado. Some patterns such as these, which can be so clearly seen on animations like this, raise new hypotheses about patterns of bird movement.
As always, we invite comment: is this a pattern supported by field observations? Quick explorations of eBird data suggest that it is. While Colorado shows similar frequency peaks for spring and fall, the fall peak in Kansas is about half of the spring peak. [When viewing these links, be sure to click on the various tabs; the map tab is the default, but the frequency tab shows the results discussed above]. While the frequency graph is most directly comparable to the STEM results above, some of the other output (like Birds/Party Hour and Average Count) shows an even more pronounced pattern.