Primates (2011) 52:373–383 DOI 10.1007/s10329-011-0258-2 O R I G I N A L A R T I C L E Copulation patterns in captive hamadryas baboons: a quantitative analysis Florian Nitsch • Sabine Stueckle • Daniel Stahl • Dietmar Zinner Received: 22 November 2010 / Accepted: 6 June 2011 / Published online: 28 June 2011 Japan Monkey Centre and Springer 2011 Abstract For primates, as for many other vertebrates, copulation which results in ejaculation is a prerequisite for reproduction. The probability of ejaculation is affected by various physiological and social factors, for example reproductive state of male and female and operational sex- ratio. In this paper, we present quantitative and qualitative data on patterns of sexual behaviour in a captive group of hamadryas baboons (Papio hamadryas), a species with a polygynous–monandric mating system. We observed more than 700 copulations and analysed factors that can affect the probability of ejaculation. Multilevel logistic regression analysis and Akaike’s information criterion (AIC) model selection procedures revealed that the probability of suc- cessful copulation increased as the size of female sexual swellings increased, indicating increased probability of ovulation, and as the number of females per one-male unit (OMU) decreased. In contrast, occurrence of female F. Nitsch S. Stueckle D. Zinner (&) Cognitive Ethology Laboratory, German Primate Center, Kellnerweg 4, 37077 Go¨ttingen, Germany e-mail: dzinner@gwdg.de F. Nitsch Department of Animal Behaviour, University of Bielefeld, Bielefeld, Germany D. Stahl Department of Biostatistics, King’s College London, Institute of Psychiatry, London, UK Present Address: S. Stueckle Department of Microsystems Engineering, University of Freiburg, Freiburg, Germany copulation calls, sex of the copulation initiator, and pre- vious male aggression toward females did not affect the probability of ejaculation. Synchrony of oestrus cycles also had no effect (most likely because the sample size was too small). We also observed 29 extra-group copulations by two non-adult males. Our results indicate that male hamadryas baboons copulated more successfully around the time of ovulation and that males in large OMUs with many females may be confronted by time or energy-allo- cation problems. Keywords Sexual behaviour Copulation pattern Papio hamadryas Akaike’s Information Criterion Introduction Effective copulation that leads to conception is crucial for successful reproduction and hence for ﬁtness. Successful copulation is affected by a number of factors, for example the quality and quantity of sperm (Birkhead and Fletcher 1995; Parker 1998) and timing in relation to ovulation (Hrdy and Whitten 1987; Dixson 1998). In primates, as in other mammals, copulation comprises mounting and intromission, at least (Dixson 1998). In any case, one decisive prerequisite for copulation to be effective is the occurrence of ejaculation. The ability of a male to provide sperm during copulation depends both on his own repro- ductive physiology and behaviour and on the reproductive status and behaviour of his mating partner. Most primate males can only copulate when females cooperate (Strum 1982; Bercovitch 1995). Copulation success can also be affected by the frequency with which males copulate given that sperm can be a limited resource in some circum- stances, as proposed by Small (1988). Such a situation may 123