Their hunting style is the opposite of a lion's. Where a pride relies on numbers, a leopard relies on absence. A stillness so complete the impala drinking ten metres away never registers her until the strike. They almost always hunt alone, almost always at twilight, and almost always finish the job in seconds. The habit of hauling kills up into trees, a fully grown impala lifted through ten metres of branches, is partly to escape lions and hyenas and partly to dine in peace over several days. Leopards are pound for pound the strongest climbers of any cat. The rosette pattern on each face is unique to the individual, the same way a fingerprint is, and researchers in Tanzania use it to identify cats from camera traps over years. The famous black panther, the melanistic leopard, does exist in Tanzania in the deep forests of the southern highlands, but they are vanishingly rare in the open savannah parks. Tanzania's leopards hold one of the strongest populations in East Africa, partly because the network of large connected protected areas gives them room to disperse without bumping into livestock. The Seronera River area in central Serengeti has been studied for decades and individual cats are known by name to the guides who work there.