Wild male gorillas weigh , while adult females weigh . Adult males are tall, with an arm span that stretches from . Female gorillas are shorter at , with smaller arm spans. Groves (1970) calculated the average weight of 42 wild adult male gorillas at 144 kg, while Smith and Jungers (1997) found the average weight of 19 wild adult male gorillas to be 169 kg. Adult male gorillas are known as silverbacks due to the characteristic silver hair on their backs reaching to the hips. The tallest gorilla recorded was a silverback with an arm span of , a chest of , and a weight of , shot in Alimbongo, northern Kivu in May 1938. The heaviest gorilla recorded was a silverback shot in Ambam, Cameroon, which weighed . Males in captivity can be overweight and reach weights up to .