1. The Social Use of Space 95 



surviving. In each experimental setting the rats experienced less disturb- 

 ance in one pen, usually pen IV, than elsewhere, since they were somewhat 

 less trapped in the behavioral sink. And yet even here only half the young 

 born survived to weaning and their growth was markedly retarded. In 

 contrast, in the pen where most rats assembled only half as many young 

 were born and only 1% of these survived to weaning. 



In addition, the abnormal frequency of social interaction resulted in 

 marked disturbance to female reproductive physiology. Near-term fetuses 

 died. Some females with such dead fetuses shortly succumbed from ap- 

 parent toxemia. Others died from massive hemorrhaging in many organs, 

 an accentuation of the event likely to have been associated with fetal 

 death. Many females who survived such events later died as a conseciuence 

 of a site of resorption of a near-term fetus becoming the focal point for the 

 development of a large abscess. Normally death occurred by the time the 

 abscess reached a diameter of 50 mm. As an example of this scourge, 56% 

 of second-generation females died by a year of age, by which time only 

 10% of males had died. 



Were a species to survive for many generations in an environment 

 fostering development of a behavioral sink, it is obvious that selection 

 must proceed to produce individuals whose behavior and physiology were 

 in harmony with such a heightened frequency of social interaction. Wher- 

 ever an environmental resource which was formerly so widely distributed 

 as to be readily available within each individual's or group's home range 

 becomes restricted, then conditions are ripe for production of a behavioral 

 sink. It is my belief that just such happenings have been the usual altera- 

 tions which have forced the evolution of horde or herd type species from 

 one previously characterized by an optimum group size of 12 adults. 



D. Yarding by Deer in Northern Wisconsin 



Characteristically since 1935 white-tailed deer (Dahlberg and Guettinger, 

 1956) in Northern Wisconsin assemble during the winter in a restricted 

 area known as yards. These cover only 5-10% of their range. Conifers, 

 which comprise the major cover in the yard, provide protection from deep 

 snows. However, such cover provides only a secondary quality food. One 

 or more feeding stations were established in most yards. During the 1930's 

 food supplements represented a small amount of total food requirements. 

 By 1953, when artificial feeding was largely terminated, most of the food 

 reciuirements were supplied at these feeding stations in many yards. 

 Nevertheless, many deer died of "starvation" even in yards where the most 

 food was provided. 



