"Predation is an important selective force in evolution and is generally assumed to select against substandard individuals, i.e. the young, senescent, sick, or individuals in poor physical condition. Raptors did not hunt randomly, but rather preferentially predate on juveniles, sick gulls, and individuals with poor muscle condition. Strikingly, gulls with an unusually good muscle condition were also predated more than expected, supporting the mass-dependent predation risk theory."