The Price of Play: Self-Organized Infant Mortality Cycles in Chimpanzees
Figure 7
Birth cohort cycling in North Group.
A) Proportion of infants in each annual birth cohort through time. Large birth cohorts (red) are separated by 3–4 years. In cases where large birth cohorts occurred in consecutive years (1991 and 1996) the first cohort is shaded red. B) Time series for the abundance of peak play (2–3 year old) infants shows a consistent cycle period of about 3.5 years. A shift in phase resulted from an Ebola outbreak in 1994.