The two lion specimens in Chicago's Field Museum are known as FMNH 23970, the 'standing' mount, killed on 9 December 1898, and FMNH 23969, the 'crouching' mount, killed on 29 December 1898. Recent studies on the isotopic signature analysis of Δ13C and Nitrogen-15 in their bone collagen and hair keratin were published in 2009. Using realistic assumptions on the consumable tissue per victim, lion energetic needs, and their assimilation efficiencies, researchers compared the man-eaters' Δ13C signatures to various reference standards: Tsavo lions with normal (wildlife) diets, grazers and browsers from Tsavo East and Tsavo West, and the skeletal remains of Taita people from the early 20th century. Interpolation of their estimates across the 9 months of recorded man-eating behavior suggested that FMNH 23969 ate the equivalent of 10.5 humans and that FMNH 23970 ate 24.2 humans.