7. Tfw Social Use of Space 41 



probability of contact because the home range centers are closer together, 

 but there exists a greater constancy of secondary reinforcers at the single 

 point of greatest probability of contact. It is for this reason that I suspect 

 that learning of signals is not likely to be effective unless home range 

 centers are 3 sigma or less apart. 



Once an animal has learned to associate a signal with the animal which 

 emitted it, there then exists the opportunity that the detecting individual 

 can perceive (hear) the signal at some distance from the emitter and make 

 the appropriate response of approach or withdrawal. How far the signal 

 may be detected depends upon both the intensity of the signal emitted 

 and the ability of the detector to hear it. Presumably, sensory capacities 

 for detection and motor capacities for emission have e\'olved simultaneously 

 and in harmony. We may then wonder as to the distance over which such 

 evolution of capacities permits the detection of an emitted signal. In the 

 absence of any experimental data, introspection suggests that one might 

 anticipate evolution of capacities to the point that an individual can just 

 detect a signal emitted at the maximum distance between home range 

 centers which still permits the learning of such signals. As we have seen, 

 this distance is equivalent to 3 home range sigma. In other words, when 

 animal A is at its home range center, a signal emitted by animal B at the 

 border of A's home range (as represented by a 3-sigma distance) reaches 

 A in just the sufficient intensity to elicit a response by A. As B moves 

 farther than 3 sigma away from A, the signal exhibits further decrease in 

 intensity. Such reduced intensity may well be perceived by A until B 

 gets at least 6 sigma away. Thus, between 3 and 6 sigma, it is suspected 

 that the signal itself is perceived but is below the threshold necessary for 

 eliciting a response by the receptor. Signals arising between 3 and G sigma 

 from the receptor are here designated as contributing to what I shall call 

 "hum." 



These characteristics of the signal are represented schematically in Fig. 

 18. A signal emitted by one animal when nearly in contact with another 

 may be given a rating of 1.0. For the purpose of later calculations, it is 

 assumed that there is an inverse decrease of intensity of the signal at suc- 

 cessive distances from the emitter until at a distance of 3 sigma it has 

 reached one-tenth of the intensity that might be recorded at the emitter. 



Investigations of this formulation requires that the sound signals emitted 

 by typical individuals of a species be recorded and other individuals of the 

 same species trained to exhibit a response upon perception of a recorded 

 vocalization. Then, in the native habitat of the species, the trained subject 

 must be moved continually farther away from the sound source until it no 

 longer exhibits the characteristic response which it had been trained to 

 perform following presentation of the signal. This distance may then be 



