Homing 353 



turtles in Paxtuxent Research Refuge, Maryland, investigated by 

 Stickel (1950), were found to average 100 m in diameter and to over- 

 lap considerably. Chameleon lizards were reported to establish ter- 

 ritories of 20 to 25 sq m in area. The arrangement of territories of 

 the wood ant is illustrated in Fig. 9.17. In this instance the ants' 

 nests were found to be only a meter or so apart. The ants foraged 

 for distances of 70 m or so, but in no instance did the members of 

 one colony encroach upon the territory of another colony. In col- 

 onies of breeding birds the private domain around each nest site may 

 be very small indeed, but this may be jealously guarded (Fig. 9.18). 



Wood mice apparently do not establish territories that are actively 

 defended, but home ranges are delineated. Some avoidance response 

 keeps the animals confined to their home ranges. The reality of this 

 action of population pressure has been demonstrated by trapping ex- 

 periments. When an area is cleared of one species— thus creating a 

 "social vacuum"— animals from neighboring areas will move into the 

 vacant area within a few days. Obviously then, the animals on the 

 periphery of the area in question did not fail to enter the area because 

 it lacked food or other necessity, or because they lacked the inclina- 

 tion to move the distances involved. The neighboring mice were 

 kept out of the area by "social" pressure of some sort resulting from 

 the presence of other members of the same species. Although animals 

 avoid entering the territory of others, peripheral contacts with neigh- 

 bors are presumably a normal condition. The rapid entry of the mice 

 into a cleared area may be due in part to a movement of the animals 

 "as if in an attempt to encounter again the stimuli produced by 

 neighbors" (Calhoun and Webb, 1953). 



The size of the territory or home range is usually larger than that 

 which would be needed for the food supply of the individual estab- 

 lishing it. In the case of territories staked out at the beginning of 

 the breeding season, it is obvious that the food supply must be ade- 

 quate for the young that are to be raised. Apparently during the 

 course of evolution reactions for establishing the territory have come 

 into existence that cause the breeding pairs to space themselves out 

 sufficiently to anticipate the food needed by the new family. The 

 size of the home range or territory has probably come to be based 

 primarily on the food supply, but in some instances it may be de- 

 termined by available breeding sites or other needs of the species. 



Homing. Frequently the attraction of an animal to the location of 

 its home is very strong; this is particularly true if the territory is 

 established in relation to a breeding site, and the reaction is further 

 intensified if young are present. The return of an animal to its ter- 



