- Slow roars. These were mainly found in the context of arrival at a particular place,
often when the food was abundant; correspondingly they often attracted other
individuals to join within 15 min of calling. - Wail pant-hoots. These were not likely to attract others to join the group. They were
given mainly in the trees when feeding peacefully or resting. - Pant roars. These were produced mainly during periods of display or arousal while
travelling or arriving. Pant roars contain no climax phase.
The four pant-hoot types are illustrated in Fig. 6.9.
Notman also concluded that listening chimpanzees can infer context from acoustic
cues accompanying the calls. Thus, if drumming accompanies pant-hoots then it is clear
that the caller is on the ground, travelling; pant-hoots with drumming were more often
responded to than other calls indicating that the caller-drummer may be interested in the
whereabouts of other chimpanzees and inviting them to respond.
Besides these general characteristics of pant-hoots, Notman (pers. comm.) considers
that individual variations may be communicatively as important as referential or
contextual meaning. They indicate whois calling. Thus listeners can tell, for example,
that Duane is calling, that he is on the ground, that he is travelling in their direction,
and they can reply to indicate their whereabouts and indicate that food is available on
their tree. Notman, like Clark and Wrangham (1994), found no evidence that the type of
food or its quality were indicated by variations in pant-hoots given when chimpanzees
were in a tree, but he did find that individuals arriving at a food tree were more likely to
call if the food on the tree was abundant ( 50% of its total capacity) than if it was
scarce. The individuality of pant-hoots may be of primary importance ( just as, in a
setting where everyone knows each other, when a person enters the room we look up and
note who they are), with the context being secondary. By contrast, in the context of
alarm calls, the meaning may be primary, as indicated below.
Human observers (our field assistants in Budongo for example) can identify many of the
members of the Sonso community by the sound of their calls; it therefore seems certain that
the chimpanzees can do the same, and studies of chimpanzees in captivity by Bauer and
Philip (1983) have proved that they can. But we don’t know whether one chimpanzee can
inform other chimpanzees about the presence or absence or activities of a third chimpanzee,
either present or not present. When chimpanzees engage in a chorus of pant-hoots at a food
tree, are they also identifying themselves and are the chimpanzees some way away, who
carefully listen to these calls, identifying the callers? It seems very likely they are. Evidence
for this comes from the response of the Sonso chimpanzees to pant-hoot choruses coming
over the forest (a loud chorus can travel up to 2 km) from another community. There is
tremendous interest, and the reaction of females may be to flee, while males may flee, be
more alert and nervous, or move towards the calls. As Wilson and Wrangham (2003) write:
The long distance over which pant-hoots are audible enables chimpanzees to advertise their
presence and numerical strength to rival communities (Clark 1993, Ghiglieri 1984) and to assess
the numerical strength of rivals from a safe distance (Boesch and Boesch-Achermann 2000).140 Social behaviour and relationships