Mammalian carnivores are apparently readily hunted. Those recorded as prey have included sable ("Martes zibellina"), American mink ("Neovison vison"), Arctic fox ("Vulpes lagopus"), red fox ("Vulpes vulpes"), and small domestic dogs ("Canis lupus domesticus"). Smaller mammals have also been recorded as prey, including northern red-backed vole ("Clethrionomys rutilus") and tundra vole ("Microtus oeconomus"). Carrion, especially that of mammals, is readily eaten during the winter. Around 35% of eagles wintering in Japan move inland and feed largely on mammalian carcasses, predominantly sika deer ("Cervus nippon"). In winter, immature Steller's sea eagles may frequent slaughterhouses to pirate bits of offal. This eagle has been recorded preying occasionally on young seals. It was estimated in one study (Brown & Amadon), that some seal pups carried off in flight by the eagles weighed at least 9.1 kg (20 lb), which (if true) would be the greatest load-carrying ever known for a bird; however, the prey weights were not verified. Often seals and sea lion of any size are eaten as carrion and, using the huge bill, may be dismembered where found rather than flown with.