170 PROCEEDINGS OF THE NATIONAL MUSEUM vol. no 



after having eaten and in cool places when food is scarce. In addition, 

 it has been postulated that warm sites may be required for the satis- 

 factory progress of some reproductive processes (pp. 171, 182). 



The bat's perception of the microclimate of its roosting site does 

 not seem to be especially good. Twente (1955b, p. 714) determined 

 that P. townsendii apparently locates a suitable roosting spot by a 

 trial and error system. If the spot first selected is unsuitable the 

 bat awakens and moves to another place. Eventually optimum con- 

 ditions may be located. The social tendency of the bats to seek their 

 own species increases the probability of most of the individuals 

 finding suitable sites. 



Sociability: P. townsendii seems as a rule not to associate in its 

 daytime and hibernation roosts with other species of bats, although 

 scattered individuals of other normally colonial species occasionally 

 may be present. Often such joint habitation does not actually bring 

 the bats into close contact, for they may occupy different parts of the 

 roosting structure or may occupy the same part at different times. 



Goldman (field notes) found P. townsendii hibernating with P. 

 mexicanus in a cave and in an abandoned mine shaft. At one time or 

 another Dalquest (1947, pp. 21-23) noted P. townsendii in the same 

 retreats as Antrozous pallidus, Myotis ealiforniGus, M. evotis, M. 

 thysanodes, M. volans, M. yumanensis, and Tadarida mexicana. Stager 

 (1939, p. 226) observed large numbers of P. townsendii, Myotis velifer, 

 and Macrotus californiGus, together with smaller numbers of four other 

 species of bats, in an abandoned mine shaft. In addition to the species 

 already noted, Pearson, et al. (1952, p. 275) found Myotis lucifugus, 

 M. subulatus, and Eptesious fuscus roosting with P. townsendii. Two 

 M. subulatus were actually in a cluster of hibernating Plecotus. I have 

 found numerous scattered dormant individuals of Myotis lucifugus, 

 M. sodalis, and Pipistrellus subflavus only a few inches from hibernating 

 clusters of Plecotus townsendii in a West Virginia cave. 



Intraspecific sociability in P. townsendii is seasonally variable. 

 Nursery colonies of females and young are common in summer, but 

 solitary pregnant females are frequently encountered. Males at this 

 season are usually, but not always, solitary. Both sexes have been 

 found together in summer roosts, though usually not clustering to- 

 gether. Winter aggregations may include a random assortment of 

 both sexes, or, according to the physical aspect and atmospheric con- 

 dition of the roost, males and females alike may tend to be solitary. 

 If there is an average seasonal divergence in roost-site selection by the 

 sexes, probably the female prefers cooler winter roosts and warmer 

 spring and summer sites than the male. 



Dalquest (1947, p. 22) noted females with newborn 3^oung gathered 

 so closely together that the edges of the cluster appeared to be a solid 



