The Evening Grosbeak is a stocky, heavy-billed finch of northern coniferous forests. 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.
The Evening Grosbeak was an object of much interest from the late 1800s to the mid-1900s, largely as a part of natural history and banding studies resulting from its eastward range expansion. Comparatively few recent studies have been conducted—surprising considering the species' extensive range. Important recent works include studies of breeding ecology and behavior in Colorado ( Bekoff et al. 1989 , Scott and Bekoff 1991 , Bekoff 1995 ), impact on forest insect pests ( Torgersen and Campbell 1982 , Takekawa and Garton 1984 ), and winter irruptions ( Bock and Lepthien 1976f , Prescott 1994 ).