Gestation period: [see also: Pregnancy] (Moss 1983: 180; Buss 1990:37; Estes 1991:265) Period between conception and birth of a calf; usually glven as 22 months. At Amboseli, Kenya, the mean gestation period was 656+4 days. Twinning occurs in less than 17% of births; Laurs (1969:205) found twins in 3 out of 222 pregnancies, whereas Moss (2001:150) found only one instance :-r:'1192 births.