Primatology.net

As described in a recently published paper in Biology Letters, the Philippine Tarsier (Tarsius syrichta) has been found to communicate through extremely high pitched vocalisations in the ultrasound domain, undetectable by human ear. These presumed mute primates baffled primatologists… How can such lack of calls be observed when closely related species are clearly dependent on frequent vocal signals within the group? However the mystery was solved when upon further inspection, these little guys could be heard communicating among the highest frequency levels detected from any terrestrial mammals. It is now thought the extremes of these calls could allow conspecifics to communicate whilst remaining undetected by predators or prey and/or allow individuals to be more easily heard through background noise.

(Ramsier et al. 2012) Primate communication in the pure ultrasound.
DOI: 10.1098/rsbl.2011.1149

A paper released this earlier this week has been first to document spontaneous prosocial behaviour in chimpanzees, finally drawing a line under the question as to whether the welfare of others is considered during choice making in this species; a controversial topic, where such behaviours have been often concluded to be absent in any primate apart from humans (generally from research within the social sciences). This research was carried out at the Yerkes National Primate Research Center by Victoria Horner, and Frans de Waal.

Pairs of chimpanzees (Pan troglodytes) where placed into testing rooms, separated by a mesh barrier. One individual had access to 30 tokens, divided into two separate colours – all of which could be given to the experimenter in exchange for food. Half of these when exchanged resulted in a selfish outcome in which only the individual handing the token received a reward, whereas the other half resulted in an altruistic outcome where both individuals received an equal reward. The individual handing the tokens to the experimenter was rewarded regardless.

If chimpanzees where choosing under a system driven by selfish interests, there should be a preference towards the choice where only the individual in control of the tokens receives a reward, and if the choice was purely random, each token would be expected to be seen 50% of the time. However, it was found that pairs where significantly more likely to share a reward (displaying prosocial behaviour), than choose the selfish option.

Victoria Hornera, J. Devyn Cartera, Malini Suchaka, and Frans B. M. de Waal (2011). Spontaneous prosocial choice by chimpanzees Proceedings of the National Academy of Sciences : 10.1073/pnas.1111088108

Long-tailed Macaques (Macaca fascicularis) were able to succeed when faced with a basic numerical test, discovers a team of researchers at the German Primate Center, Goettingen. Researchers Vanessa Schmidt and Julia Fischer developed a basic test where an individual was presented with two plates, each containing a different quantity of pebbles, and where the plate with the largest number of pebbles gave a greater reward. The macaques were able to understand the concept of relative quantities, and choose the correct option at 80%+ success rate.

Although experimentation testing these types of numerical skills are not new, previous studies used edible items where the subject may eat the amount of food on the plate in which they choose – this experiment yielded only a 69% success rate in this study, and showed that the impulsiveness to gain a reward that they could see impaired their judgement when making a choice. Therefore previous studies may have underestimated the animals’ ability.

More information at; BBC – Earth News

Schmitt, V. & Fischer, J. Representational format determines numerical competence in monkeys. (2011). Nat. Commun. 2:257 DOI: 10.1038/ncomms1262.

When trained Macaques were given a choice of three answers in a computer game; one of which was correct, one incorrect, and an additional option to pass – macaques where shown to choose the latter option to pass rather than risk being incorrect. The macaques were rewarded for a correct answer, but an incorrect answer initiated a pause in the game until the next question.

The “pass“ option was used in an identical fashion to that of human participants, and the macaques were observed to show self-doubting behaviour – a trait which was previously thought to be unique to us. When capuchins were faced with an identical challenge, they failed to take this third option, and seemed unaware when they are likely to make an error.

More information and Video at; BBC – Earth News

Sexual competition can be highly disruptive of group relationships, especially if conflicts are escalated into a fight – so it is important for third-parties to “keep track” of consortship partners within a group in order to take appropriate action and possibly avoid such confrontations. De Marco et al. collected data from 2 Tonkean Macaque groups, to test whether attention from third-parties would be directed towards actively consorting group-mates and to then see if activities are modified, or if stress levels increase.

They found that the dominant male was approached more frequently when involved in a partnership with an estrous female. But also found that although females gain more attention during estrous, levels of interactions with the female during consortship did not change comparatively to the control. De Marco et al. also found that levels of sleeping and environment manipulation from bystanders were significantly reduced during times of sexual pairing; this study is the first to demonstrate a change of group behaviour in primates during times of sexual consortship.

Read more of the study at;
De Marco, A. Cozzolino, R. Dessì-Fulgheri, F. Thierry, B. 2011. Interactions between Third Parties and Consortship Partners in Tonkean Macaques (Macaca tonkeana). Int J Primatol DOI: 10.1007/s10764-011-9496-9