The Signal Must Be Costly.
This explains so much, somehow.
The basic idea behind [the costly-signaling] hypothesis is that animals need a means to communicate, i.e., to signal to kin and strangers their abilities, intentions, and fears. In order for individuals to trust the veracity of the information that is presented, it is argued that the signal must be costly to produce. If it were not costly to communicate, then individuals would regularly lie and cheat.
The classic costly signal is the peacock’s tail. The tail makes the bird more vulnerable to predators, but the message to the potential mate is, “I have survived in spite of this huge tail, hence I am fitter.” Similarly, it is possible that mobbing behavior is an honest signal by which adult male tarsiers advertise their quality as potential mates. The idea of mobbing as a costly signal is intriguing, because by approaching a predator, an individual can advertise very specific information. While aggregating around a potentially lethal snake, tarsier males may demonstrate their current physical condition, agility, and speed. This information would be very useful for a subadult female who is making a decision about whether to stay longer in her parental group, or disperse and establish her own group. Mobbing may be a way for young females to evaluate the ability and willingness of males to protect them and their future offspring against potential predators. The observation that males are more likely to join mobbings outside their territory [especially when subadult females are present] provides some potential indication that intense mobbing by spectral tarsiers males may represent costly signaling.
~ Sharon Gursky, “Function of Snake Mobbing in Spectral Tarsiers”
American Journal of Physical Anthropology 129:601–608 (2006)
Ambiance 
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