Migration Info It is hard to miss the arrival of Rose-breasted Grosbeaks in the spring, as the males sing their bright, cheerful songs throughout the day while they establish their territorial boundaries. Mature males (second year and older) arrive first, about three days ahead of the females. First-year males are last to arrive; these birds, which look more or less like females, also arrive in a predictable order: "bright" individuals come first, the dullest birds (those that look most like juveniles) last. (It is believed that the dull birds are those that experienced a less extensive molt, possibly due to poorer nutrition on the wintering grounds.) Females will sometimes mate with first-year males, and when they do, they usually choose the bright individuals. This species has been arriving earlier each spring for about the last 20 years, possibly as a result of climatic change due to greenhouse gases in the atmosphere.