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  • Author or Editor: Richard Byrne x
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Abstract

When spider monkeys (Ateles geoffroyi) are dispersed and moving through wooded areas in the dry forest of Santa Rosa National Park in Costa Rica, they give loud calls, whinnies, that can be heard over long distances and appear to be answered with the same call from other monkeys. We examined the circumstances in which this vocalization was emitted and the responses elicited from other group members. A total of 105 h of continuous recordings on emission of whinnies, 113 h of individual focal samples and 291 spectrograms were analyzed from a study group with 15 identified subjects. Whinnies emitted in different circumstances caused different reactions. Whinnies provoked by the sight of an observer were never responded to in any particular way, while those given during resting or feeding sometimes caused an active response of approach or calling. Most strikingly, whinnies given during group movement provoked hearers to approach or call significantly more often than either those given while feeding or resting. Playback experiments found one response, 'scan', to differ according to the original circumstances of emission of the broadcast call: monkeys scanned more in the direction of the sound when hearing feeding rather than group movement whinnies.

In: Behaviour

Abstract

Mountain gorillas use elaborate, multi-stage procedures for dealing with plant defences. This paper investigates the use of mathematically-inspired, informational measures to gauge the complexity of one of these tasks, eating thistle Carduus nyassanus, from field observations of 38 adults and juveniles. Behaviour was analysed at two levels, a detailed, movementbased description of the form of actions, and an organizational description of techniques that were composed of a series of many actions. Complexity, as measured by counting the sizes of behavioural repertoires, correlated at the two levels. Repertoires were shown to be incomplete, but the rates of cumulative increase in actions differed between tasks. Thistle eating was the most complex, and apparently involved many more actions than even chimpanzee tool-use. Techniques were highly selective arrangements of actions, so that their organization (sequence, bimanual coordination, hierarchical structure) reflected cognitive capacity. Although ideally it would preferable to estimate complexity of task organization, this may seldom be feasible, and was not in this case. Instead, the length of a regularly occurring sequence of actions may be the best practical estimate of an underlying complexity of mental process. Confidence in this measure will be increased if it broadly agrees with other, independent estimates of task complexity; in the case of gorilla plant processing, both the size of repertoire of functionally distinct actions and the degree of lateral specialization were, like sequence length, greater for thistle processing than for other tasks studied to date.

In: Behaviour

In a field experiment, tape-recorded vocalizations of spider monkeys (Ateles geoffroyi) were played back to investigate whether individuals were able to discriminate between group members and strangers. Monkeys responded remarkably similarly in the two cases, with no significant difference found between the numbers of calls given by an individual, or the types of call given. However, a group was more likely to give some vocal reaction when hearing a stranger’s call than when hearing one from an individual of their own community. Further, the only instances in which agonistic territorial behaviours occurred were in reaction to strangers’ playbacks. No significant effects on the response given were produced by the sex of the caller, the location and time of day of the broadcast, the size of the subgroup hearing the call or the activity in which they were involved. These results are discussed with respect to acoustic, social and ecological factors that may lead to the apparent lack of vocal discrimination of strangers within the community range.

In: Folia Primatologica

Abstract

Animals with visual perspective taking abilities should differ in their responses to individuals that do and individuals that do not have visual access to some critical event. We investigated whether domestic pigs show behaviour consistent with this ability. Ten subjects were trained to move from a start box into one of four corridors that they had seen a human enter with a bucket for baiting. They received a food reward for choosing the correct corridor. In unrewarded probe tests, the subjects' view of the corridors was blocked, but they could see a 'seeing' companion pig who had visual access to the baiting event, and another, whose view was also blocked, located in start boxes to their left and right. After the companions had been released and entered corridors, the subject was released and which companion it followed was recorded. Eight pigs followed companions less frequently than expected by chance, probably due to specific corridor or centre/side preferences. However, one subject showed no positional bias, and a significant preference for following the 'seeing' companion, consistent with the ability to take another's visual perspective. Our design rules out learning of a correct response during the experiment, by testing subjects in unrewarded probe trials, and by using companions that were equally trained and unaware of the subject's task. However, we cannot rule out the possibility that previously learned contingencies were used to solve the problem. We therefore consider that this apparent visual perspective taking ability does not necessarily imply any ability to understand knowledge states.

In: Behaviour

In the Mahale Mountains National Park of Tanzania, a group of about 33 chimpanzees were observed to surround a leopard den containing a mother and at least one cub and to drag out and kill the cub. This is the first report of chimpanzees or any other primate species killing their potential predator’s offspring. The incident suggests that chimpanzees, without any weapons, can manage to defend themselves against a carnivore of at least up to leopard size, and implicates how the early hominids may have reacted against their potential predators.

In: Folia Primatologica

Abstract

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.

In: Behaviour