76 John B. Calhoun 



ground runways. Presumably such behavior enables these species to reduce 

 the frequency or intensity that they experience by the vocalizations of 

 their dominant associates. When Dr. Barbehenn first joined me in these 

 studies of small-mammal communities he insisted that the only effective 

 way of trapping Blarina was to set traps at points where excavations in 

 humus revealed underground runways. However, it had been my experi- 

 ence with continuous removal trapping, where traps were set at fixed 

 intervals from stations without any regard to underground runways, 

 that once the dominant Peromyscus has been removed Blarina were caught 

 on surface sets with equal ease as earlier for Peromyscus. Therefore, when 

 he initiated his Chadwick Woods study (Fig. 10) he set his traps on the 

 surface without regard to runways. During the initial days while many 

 Peromyscus still survived, most Blarina were taken only by traps acci- 

 dentally set by underground runways. As the number of Peromyscus 

 became fewer and fewer by the removal trapping, not only were more 

 Blarina caught, but also an increasing percentage of these had so entered 

 traps as to indicate clearly that they had been wandering about the surface 

 and were not emerging through the leafmold below the trap. Thus, a re- 

 duction in crypticism accompanied enlargement of home range. This same 

 change in behavior characterizes the typically subterraneous mouse Pitymys 

 following removal of its dominant associates. The prior discussion of the 

 special case of both bodily movement and vocalizations of another in- 

 dividual become important here. We might thus expect that vocalization 

 of shrews would become reduced as they become more cryptic in the 

 presence of dominant mice. Also as mice are removed from the habitat, 

 shrews should not only spend more time out on the surface, but they 

 should vocalize more. 



This section cannot be closed without brief reference to the meadow 

 mouse Microtus. Data from a recent unpublished study by Dr. Barbehenn 

 in an abandoned orchard in Maryland suggest that this genus represents 

 one terminal phase in this evolution of types, which on the psychological 

 level enables successively evolved types to acquire a more dominant posi- 

 tion with reference to the use of space. At points isolated from each other 

 by at least 600 feet he placed covered feeding stations which contained 

 rolled oats mixed with dyes which stained the fur of animals eating there. 

 Daily removal of food increased for nearly a month, after which the daily 

 removal fluctuated about an asymptote for another month. At the end of 

 this time removal trapping was conducted along a circular trapline having 

 a radius of 150 feet from the feeding station. Practically all the Peromyscus 

 taken were marked with the red dye, but no Microtus were so marked. 

 This indicated that Microtus living at this distance from the feeding sta- 

 tions were not only unaffected by it, but their home ranges were unaffected 



