Cougars have an eclectic diet, generally eating what they encounter, when they encounter it. When deer bunch together in the winter, cougars find and eat more deer. In summer, when deer scatter more widely, the cougar adds rabbits, birds, porcupines, squirrels, raccoons, rats, and even grasshoppers to the menu. The cougar's hunting prowess is best put into perspective by comparing body weights of predator and prey. When deer are not available, a cougar can kill an elk or moose six or seven times as large as itself.
Predation is an iffy business, and every successful stalk can be preceded by several failures.
A cougar may hit 40 mph in a sprint, but it has little stamina and must catch its prey in a few bounds or give up. The Houston Zoo has a pair of cougars on display.