On 12 April 2021, we observed a Black-billed Magpie (Pica hudsonia) kill an apparently-healthy adult female Cassin's Finch (Haemorhous cassinii) in an urban backyard near a feeding station in Missoula, Montana. The magpie landed on a chain-link fence above the finch before dropping to the ground 1–2 s later where it grabbed the finch with its bill and pinned it to the ground with a foot, then delivered several blows of the bill to the finch's neck, back, and breast. The entire attack, from arrival of the magpie to its departure with the apparently-dead finch held in its bill, lasted no more than 60 s. We found only 2 prior reports of Black-billed Magpies capturing adult birds, and none for the Yellow-billed Magpie (Pica nuttalli). There are several published cases of the closely-related Eurasian Magpie (Pica pica) attacking and killing adult birds, indicating that magpies are quite capable of subduing birds if so motivated when given the opportunity. Black-billed Magpies and Eurasian Magpies tended to attack adult birds during winter through spring (non-breeding season), and most often in urban environments where small birds aggregate near concentrations of food or potential roost and nest sites, resources also attractive to magpies. These circumstances may afford magpies more close encounters with potential adult avian prey than might occur in rural locations, and may encourage them to hunt adult birds more frequently.