diet in certain areas, such as Dama and Dorcas gazelles in the Sahara, impala in the eastern and southern African woodlands, springbok in the arid savannas to the south and Thomson's gazelle in the Serengeti. Smaller antelopes like the common duiker are a frequent prey in the southern Kalahari. Larger ungulates are typically avoided, though nyala, whose males weigh around , were found to be the major prey in a study in the Phinda Game Reserve. In Namibia cheetahs are the major predators of livestock. The diet of the Asiatic cheetah consists of chinkara, desert hare, goitered gazelle, urial, wild goats and livestock; in India cheetahs used to prey mostly on blackbuck. There are no records of cheetahs killing humans. Cheetahs in the Kalahari have been reported feeding on citron melons for their water content. Prey preferences and hunting success vary with the age, sex and number of cheetahs involved in the hunt and on the vigilance of the prey. Generally only groups of cheetahs (coalitions or mother and cubs) will try to kill larger prey; mothers with cubs especially look out for larger prey and tend to be more successful than females without cubs. Individuals on the periphery of the prey herd are common targets; vigilant prey which would react quickly on seeing the cheetah are not preferred. Cheetahs hunt primarily throughout the day, sometimes with peaks at dawn and dusk; they tend to avoid larger predators like the primarily nocturnal lion. Cheetahs in the Sahara and Maasai Mara in Kenya hunt after sunset to escape the high temperatures of the day. Cheetahs use their vision to hunt instead of their sense of smell; they keep a lookout for prey from resting sites or low branches. The cheetah will stalk its prey, trying to conceal itself in cover, and approach as close as possible, often within of the prey (or even farther for less alert prey). Alternatively the cheetah can lie hidden in cover and wait for the prey to come nearer. A stalking cheetah assumes a partially crouched posture, with the head lower than the shoulders; it will move slowly and be still at times. In areas of minimal cover the cheetah will approach within of the prey and start the chase. The chase typically lasts a minute; in a 2013 study, the length of chases averaged , and the longest run measured . The cheetah can give