males of intermediate rank, whereas the alpha male is able to monopolize females
when it suits him to do so.
Considering the data for the year 2001, 149 copulations were recorded. For each
observed copulation we recorded the approaching chimpanzee.^50 Females approached
more often than males, the highest number of approaches being made by Nambi (alpha
female, 12.8% of all approaches), Gonza (11.4%), Melissa and Clea (8.7% each) and
Kwera (7.4%). Black and Nick scored highest for males, with 6% each. Tinka, the
omega male, made just one approach (0.7%). Interestingly, Duane, the alpha male, made
only two approaches (1.3%), and no male scored more than 6% on approaches.
Comparing this with the number of copulations, we find that Gonza, a young female
just becoming adult, received the highest number of copulations with 20.8%, followed
by the alpha female Nambi (14.8%), Melissa (12.8%) and Clea (10.1%). We thus see
that the females who made the most approaches also received the highest number of
copulations.
In the case of males, the highest copulation frequency was for Duane with 15.4%,
followed by Nick with 14.1%, Black with 11.4% and Zefa with 8.7%. These males did
not often approach females for copulation, preferring to be approached by them.
Interestingly, as pointed out by Newton-Fisher (2004), Vernon, the second highest
ranking male after Duane in terms of respect shown to him by other males (pant-grunt
frequency), had throughout his life a low copulation frequency quite out of keeping with
his rank. In addition, as our genetic studies show (Appendix C) he failed to sire any off-
spring. This is surprising and raises the question why he did not benefit reproductively
from his close relationship with the alpha male Duane. At present we have no answer to
this question.
The circumstances surrounding copulation in chimpanzees can be illuminative of
chimpanzee relationships. Here is an example from my field notes of an unwilling female:
Friday 4th October 1996.
Zimba in oestrus 4, Bwoya, Magosi, Duane, Kikunku all in attendance. They rush about. Chris &
Zesta arrive; they fight in the trees. Much noise and excitement. The 4 adult males groom each
other (not Zesta and Chris) on the ground, for a long time, totally unconcerned by us but looking
up into the canopy from time to time to where Zimba is sitting. Then noise again and they climb up
but can’t reach Zimba who screams and keeps up in the thin branches so when they move near the
branch sways and down she leaps to a new branch or tree. She doesn’t want to mate it seems and
they are getting frustrated! All morning this goes on.In the above case, Zimba did not want to mate. Often the reverse is the case but even
then things are complicated. For example, there was an occasion when Nambi, the alpha
female, was in oestrus; her sexual swelling had been increasing in size for three days
and she was now approaching maximum swelling and ovulation. During the preceding
days she had been accompanied by a number of subadult and adult males; they had been
116 Social behaviour and relationships
(^50) That is, the one making a physical approach; in some cases the approach was preceded by a signal from
the male, e.g. a branch-wave. Records are not sufficiently detailed to record all occasions when this occurred.