Prey selection varies according to habitat and season, with lions being capable of overpowering a wide variety of herbivores, including wildebeest, zebras, topi, hartebeest, warthogs, buffalo, giraffe, impalas and gazelles. Lions usually kill their prey by strangulation, though very large animals such as buffalo are suffocated by one of the lions clamping its jaws over the animals mouth and nose. When plenty of food is available lions gorge themselves, with males eating up to 90 lb (41 kg) on an empty stomach, while lionesses can consume 60 lb (27 kg). This is four to five times their average daily requirement, and is an adaptation to a feast or famine regime; predators can never be sure of when they will next eat.