and Hiraiwa-Hasegawa (1990) working at Mahale define ‘copulation’ as one or more
mountings taking place over a maximum period of 10 min. If there is an interval of more
than 10 min between mountings, they consider that a second copulation is taking place.
Sometimes a vaginal plug of coagulated seminal fluid can be seen at the vaginal
entrance after copulation, or dislodged when the next copulation takes place.
A study of female mating patterns in the Sonso community was made by Oliver
(2002). She collected data from June to December 2000, and combined her own obser-
vations with data collected by BFP field staff over the previous five years. All except one
of the copulations observed took place in a group setting; the single exception was a
case of copulation with just the pair concerned present. She compared the patterns of
sexual behaviour of the Sonso females with those reported in several long-term field
studies at Mahale and Gombe.
Two main kinds of copulatory relationship were distinguished: ‘opportunistic’, in
which a female copulated with a second male within an hour of copulating with the first
male, and ‘possessive’ or ‘restrictive’, in which a female did not copulate with a second
male for at least an hour after copulating with the first, despite a second male being
present in the party. Of the copulations she analysed 84% were opportunistic, while
15.8% were possessive. These proportions are not dissimilar to those reported for
Gombe (73% opportunistic, 27% restrictive; Tutin 1979) or Mahale (73% : 27% in one
community, 93% : 6% in another community). Copulation frequency of females was
measured by Hashimoto and Furuichi (in press) at Kalinzu Forest; the mean for 329
copulations was 2.7 copulations per hour. One female copulated 6.8 times per hour over
a 343 min period. Promiscuity was very marked in all except one female, for example
the female Ha copulated with 9 of 11 males who were observed in the same tree during
a 52 min period. For males, the greater prevalence of opportunistic mating over
possessive mating reflects the fact that they may be unable to prevent other males from
mating with any given oestrous female even if they want to. Vaginal plugs, whatever
their function may be, do not prevent this.
Unlike at Gombe and Mahale, female age in Oliver’s study did not correlate with the
proportion of possessive copulations although the alpha male did focus on older
females and possess them (see below). Hasegawa and Hiraiwa-Hasegawa (1983) and
Tutin (1979) report that in Mahale and Gombe respectively possessive matings were
more frequent in the case of older, resident females than in younger, immigrant
females. Also, there was no difference in the proportions of promiscuous matings
by younger, immigrant females and older, resident females at Sonso (promiscuity
was measured by the number of different mating partners a female had during a given
observation session). However, a significant positive relationship was found between
male rank and copulation rateswith older females. Thus, at Budongo, high ranking
males copulated more frequently with older females but did not possess them more
often.
Male alpha rank was correlated with the number of possessive copulations, and the
majority of possessive copulations were found in the alpha male (57%). Apart from the
alpha male, however, the correlation was not statistically significant, and it seems that
118 Social behaviour and relationships