Mountain gorilla reproduction and sexual behavior.

Data on mountain gorilla reproductive behavior, demography, and sexual behavior are reviewed and compared with earlier reviews of reproduction by wild gorillas and with data on captive gorillas. Topics covered include maturation, female transfer patterns and reproductive histories, reproductive intervals, influences on fertility, infant mortality, sex ratios at birth, birth seasonality, copulatory behavior, and estrus cyclicity. Most of the results of the updated analyses presented here corroborate those from previous studies of the same population. Newer information shows that responsibility for the initiation of copulations varies in association with female fertility and sexual state; that infant mortality in the first year is higher than reported earlier; that the sex ratio at birth is 1:1; and that, on a population level, interbirth intervals following the birth of males are the same length as those after female births. Data on reproductive intervals, sexual cyclicity, and copulatory behavior are generally similar to data from many captive situations. Two findings are particularly relevant to the problem of cessation of reproduction by captive females. First, fertility does not obviously decline with age in the wild. Second, a high proportion of females have reproduced in their natal groups and some have had multiple births there.