Birth seasonality and interbirth intervals in free-ranging Formosan macaques, Macaca cyclopis, at Mt. Longevity, Taiwan

The birth season of Formosan macaque, M. cyclopis during our study started in February and ended in August M with a peak in the second half of Apl il acid the first half of May. The average birth rate was 82% +/- 21 for 114 f emales with four years of breeding records. Our study reports that a time s pan of one year between births can be considered as the norm for the wild M . cyclopis. Of the 288 interbirth intervals (IBI), 88.5% showed a 1-year in terval (mean 364 +/- SD 29 days); 11% showed 2-year interval (727 +/- 36 da ys); and 1% (2 females) had 3-year interval (range 1030-1040 days). The IBI For females that had infant loss within six months of life were the shorte st. But there was no significant difference from that of females that had s tillbirth (p > 0.9) and infant that survived for first six months of life ( p > 0.06). However, among 255 cases of 1-year IBI, stillbirth or following infant loss within six months of life did significantly shorten IBI for ten days (F-1.253 = 5.74, p < 0.05).