Behaviour 143, 10 (October 2006)
http://www.ingentaconnect.com/content/brill/beh/2006/00000143/00000010
da Cunha, RGT & RW Byrne (2006) Roars of black howler monkeys (Alouatta
caraya): evidence for a function in inter-group spacing. Behaviour 143:
1169-1199.
Loud calls can be expected to play an important role in the lives of howler
monkeys, given the specialised anatomy of howler vocal apparatus and the
time and energy invested in calling. Here we present observational and
experimental data aimed at understanding the function(s) of the roars of
black howler monkeys (Alouatta caraya). Most roars were given spontaneously,
especially around dawn, although inter-group encounters and extreme weather
events triggered calling. Roars were given throughout the home range, but
not uniformly; variations in calling frequency with location were not well
predicted by frequency of use, and calling was not more frequent at borders.
Predator presence was neither necessary nor sufficient to stimulate calling.
We experimentally played back loud calls from stranger groups, either inside
the home range of the study group, simulating invasions, or in border areas.
In response to simulated invasions, the alpha male roared more frequently
than expected, usually in the vicinity of the playback site, moved off
sooner and travelled to or near to the playback site. When playback was in
border areas, the alpha male roared infrequently and significantly later,
and did not travel towards the playback site. These results are not
consistent with the hypotheses that roaring functions in predation
deterrence and/or mate defence. Instead, they suggest that roaring allows
regulation of the space use, by means of regular advertisement of occupancy
but not by mutual avoidance or boundary defence. We believe that roars also
provide a mechanism for reinforcing occupancy during encounters, and may
sometimes serve to settle disputes without chases and fights.
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