Mammals of Porter Co^m.ty 



217 



taken only two were adult, one was nursing and the other contained 

 four fetuses, each about 20 mm. in length. 



This species although closely resembling the more common northern 

 deer mouse is readily distinguishable in the adult state by its darker 

 coloration and more sharply bicolored tail, as well as by its smaller size, 

 shorter hind foot, and shoi'ter tail. Immature specimens of the two 

 species are almost indistinguishable in point of color, but are apparently 

 easily distinguished by measurements. Five adult or nearly adult males 

 give these extreme and average measurements: total length 150, 141, 130; 

 tail 62, 57, 52; hind foot 18, 17.7, 17 mm. Two adult females measure re- 

 spectively, 148, 137; 60, 52; 17, 18 mm. 



One of the specimens of this species was infested in the inguinal 

 region with a fly larva, similar to the one found in the northern deer 

 mouse. 



Fig. 3. Habitat of Baird's Deer Mouse, Peromyscus vianiculatus bairdii, the low 

 fore dunes in the foreground covered with Calamoinlfa longifolia. 



Prairie vole (Microtus ocJirogaster Wagner) : Represented by seven 

 specimens, three adult or nearly so and four young. Three of the speci- 

 mens, an adult and two young were taken in a wooded dune, though near 

 a meadow, in subterranean runways in traps specially set for pine voles. 

 The others were taken in an interdunal meadow in traps placed at 

 random on the ground as no runways were discernible. Although traps 

 were placed in four different interdunal meadows, in only one were these 

 voles taken. It may be that colonies are somewhat local in distribution. 

 One female was nursing, mammae: pectoral 1/1, inguinal 2/2^6. Three 

 stages of growth appear to be present, breeding adults, half grown young, 

 represented by four immature specimens, and very young represented by 

 those belonging to the nursing female. Hahn (4) records this vole as 

 being rather generally and commonly distributed throughout the state. 

 Dice (2) found it common in Berrien County, Michigan. 



