Since this bird has interesting natural biology related to its migration, I copied this from Cornell Lab of Ornithology's Birds of America online: "An irruptive migrant across much of its range, it makes roughly biannual appearances at winter feeding stations throughout much of the coterminous United States. Often moving in large flocks, this boldly colored bird with the massive bill is difficult for observers to miss. During the breeding season, however, the species is quite secretive, and courtship occurs without elaborate song or display. This secretiveness, together with a spare, flimsy nest placed high in a tree, makes it a difficult subject of study. As a result, comparatively little is known of the species’ life history.
The breeding range of the Evening Grosbeak underwent a significant expansion in historic times. The contemporary scientific literature documented eastward movement, with the species regularly appearing in areas east of its known range, perhaps a result of the establishment of box elder (Acer negundo) in eastern cities as an ornamental planting. The abundant seeds of the box elder persist on the tree through the winter, providing a stable food supply. Outbreaks of forest insects may also have allowed this bird to extend its breeding range to the east."