Nile crocodiles are apex predators throughout their range. In the water, this species is an agile and rapid hunter relying on both movement and pressure sensors to catch any prey unfortunate enough to present itself inside or near the waterfront. Out of water, however, the Nile crocodile can only rely on its limbs, as it gallops on solid ground, to chase prey. No matter where they attack prey, this and other crocodilians take practically all of their food by ambush, needing to grab their prey in a matter of seconds to succeed. They have an ectothermic metabolism, so can survive for long periods between meals—though when they do eat, they can eat up to half their body weight at a time. However, for such large animals, their stomachs are relatively small, not much larger than a basketball in an average-sized adult, so as a rule, they are anything but voracious eaters. Young crocodiles feed more actively than their elders according to studies in Uganda and Zambia. In general, at the smallest sizes (), Nile crocodiles were most likely to have full stomachs (17.4% full per Cott); adults at in length were most likely to have empty stomachs (20.2%). In the largest size range studied by Cott, , they were the second most likely to either have full stomachs (10%) or empty stomachs (20%). Other studies have also shown a large number of adult Nile crocodiles with empty stomachs. For example, in Lake Turkana, Kenya, 48.4% of crocodiles had empty stomachs. The stomachs of brooding females are always empty, meaning that they can survive several months without food.