Interannual variability in fruit abundance and the reproductive seasonality in Sumatran Long‐tailed macaques (Macaca fascicularis)

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Abstract
In an environment with a seasonal food supply, most primate species show birth peaks which precede the peak food period by some two to five months. Sumatran Long‐tailed macaques (Macaca fascicularis), however, showed birth peaks during or after the fruit peak. Years of high birth rates and early birth peaks alternated with years of low birth rates and late peaks. The timing of births was strongly influenced by a female's condition, which depends on food supply and her previous reproductive history. Pregnant females were more active than other females, whereas females with young infants were less active.The unusual timing of births is ascribed to the unpredictability of the height of the annual fruit peak. This hypothesis is supported by the reproductive patterns of other South‐east Asian primates and by a model comparing the two types of reproductive timing. Further differences between the two strategies of reproductive timing are predicted.