Bonaparte's Gull first cycle

Aged by dark carpal bar, dark secondary tips, dark on first primary, and dark tail band. From first-cycle Black-legged Kittiwake by lack of black hindcollar (sometimes less obvious or lacking in first-year kittiwakes), less black on primaries, and less obvious brownish (not black) carpal bar. From Little Gull first cycle by lack of dark cap, less prominent carpal bar, and more dark on secondary tips.