The Dickcissel is one of the most typical and abundant breeding birds of North American prairie grasslands, with a primary breeding range (Figure 1) centered, almost bull's-eye-like, on that biome. Despite this biogeographic affinity, this species is notorious for regular seasonal movements within its primary breeding range and for irregular movements outside of this core range to breed in surrounding areas where extensive grassland habitat exists. These erratic, semi-nomadic movements result in dramatic year-to-year changes in distribution and abundance, especially in peripheral and sporadically occupied areas. Most Dickcissels winter in the llanos region (seasonally flooded grasslands and savannas) of central Venezuela, but again, some birds move around the winter range and occasionally spend part or all of the nonbreeding season in other areas of Central and South America.
On both breeding and nonbreeding ranges, the Dickcissel has had to adjust to major habitat changes, as natural grasslands and savannas have been largely replaced by agriculture, but it seems to have adapted well to many secondary habitats, and even thrives in some agricultural landscapes. The species has been quite well studied on both its breeding and nonbreeding ranges for several reasons: It shows unusual, at times almost nomadic, shifts in distribution. and abundance within its breeding and wintering ranges ( Gross 1921 , Gross 1968a ; Fretwell 1986 ); it has a polygynous mating system ( Zimmerman 1966b ); it forms huge flocks and roosts during the nonbreeding season ( Basili and Temple 1999b ); it is a pest on agricultural crops throughout its winter range, especially in Venezuela ( Basili and Temple 1995 , Basili and Temple 1998 ); and it is of conservation concern, having suffered severe population declines (Fretwell Fretwell 1977 , Fretwell 1979 ; Basili and Temple 1995 ). Most recent and ongoing studies on the breeding range have been motivated by interests in how changing land-use practices (for example, large-scale restoration of grassland through the Conservation Reserve Program) in the core breeding range affect nesting birds. On the winter range, most recent and ongoing research has focused on the bird's relationship with cereal crops and how to lessen the impacts of lethal control efforts undertaken by aggrieved farmers. Still, as this review will reveal, many aspects of its biology remain unstudied.