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Seasonal variation in fecal testosterone levels in free‐ranging male Japanese macaques

Seasonal variation in fecal testosterone levels in free‐ranging male Japanese macaques (Macaca fuscata) was examined with reference to their dominance rank and age class. Six adult (≥7 years old, three higher‐ranking and three lower‐ranking) and four adolescent (5–6 years old, two higher‐ranking and two lower‐ranking) males were selected as target animals. Fecal samples of these males were collected during the first 3–5 days of each month and analyzed by the method developed by Barrett et al. [Primates 43:29–39, 2002b]. Testosterone levels varied significantly across the 12 months, and were highest in the early and middle parts of the mating season (i.e., October and November). Higher‐ranking adult males displayed a peak testosterone level in October, whereas lower‐ranking adults had no clear peak in the mating season. Such a difference in testosterone peaks in males could provide higher‐ranking males more opportunities to fertilize females at first ovulation in the mating season than lower‐ranking males. Am. J. Primatol. 69:603–610, 2007.© 2007 Wiley‐Liss, Inc.