Reproductive seasonality in wild northern pig-tailed macaques (Macaca leonina)

Macaque reproductive patterns range from strictly seasonal breeding to non-seasonal breeding, but factors explaining this variation are not fully understood. Valid reproductive seasonality data are also still lacking for many wild macaque populations because the majority of birth data are from captive animals living outside of their geographic range. We evaluated whether the reproductive seasonality of wild northern pig-tailed macaques falls as expected by the ecological (latitude) or phylogenetic inertia hypotheses in comparison with other macaque species. We recorded monthly occurrences of births (N = 22), copulations (N = 563), and females exhibiting sex skin swellings (N = 18) in one group at Khao Yai National Park (KYNP), Thailand. Births, copulations, and females exhibiting sex skin swellings were significantly different from a random distribution. Using measures of circular statistics and the van Schaik and colleagues' (Schaik et al. Lee (ed), Comparative primate socioecology, Cambridge University Press, Cambridge, 1999) seasonality categorizations, the population at KYNP is best characterized as moderately seasonal breeding. Despite some inconsistency, macaque reproductive seasonality was significantly influenced by latitudinal location. We broadly found that: (1) non-seasonal breeding macaque populations (birth r-vector < 0.3) lived at latitudes close to the equator between 1°S and 3°N, (2) moderately seasonal breeding macaque populations (0.3 < birth r-vector < 0.7) were found between 3°N and 14°N and at 5°S, and (3) strictly seasonal breeding macaque populations (birth r-vector > 0.7) ranged ≥ 12°N. A strong phylogenetic signal in reproductive seasonality on the macaque phylogeny was also detected. However, further studies of wild macaque populations are still needed to better characterize reproductive seasonality in this taxon.