MAMMALS OF MARTLANB 



121 



Remarks. — It is generally believed that the black rat was the com- 

 mon rat of the eastern United States before the late 18th century. 

 Around that time, it is said, the Norway rat was introduced, and be- 

 cause it is a larger and more aggressive animal it drove the black rat 

 out except near shipping ports (see Bailey, 1923, p. 114). There is 

 however, no real evidence that the black rat was ever well established 

 in Maryland or in any other Northeastern State. This animal prefers 

 a warm climate and probably found Maryland too cold for its liking. 

 Moreover, it is known that in areas in the South the black rat and the 

 Norway rat live in the same habitations without one species driving 

 away the other. In areas where the two species live together, however, 

 there seems to be an ecological separation in that the black rat usually 

 is found in the upper stories of a building, while the Norway rat in- 

 habits the basement and adjacent sewers and tunnels. 



At the present time there are no known colonies of this species in 

 Maryland, although perhaps a few animals inhabit some of the build- 

 ing along the docks in Baltimore City. In 1949 Davis and Fales (1949, 

 p. 248) reported them present in only three Baltimore buildings and 

 estimated the population as not more than 1,000. This rat, however, is 

 the common ship variety and probably has been, and will continue to 

 be, repeatedly introduced into the Baltimore wharf district. 



As far as is known, none are established now in Washington, D.C., 

 although here again they may leave boats and take up residence in 

 nearby buildings. Five specimens have been taken in the District of 

 Columbia. Three of these were removed from a boat that had docked 

 at the Seventh Street Wharf in April 1923, and two were trapped in 

 January and February of 1912 at the old Central Market, to which 

 they apparently had been brought in baskets of fruit from Egypt. 



NORWAY RAT 

 Rattus norvegicus (Berkenhout) 



Mus norvegicus Berkenhout, Outlines of the natural history of Great 

 Britain and Ireland, 1 : 5, 1769. 

 Type locality. — England. 



General Distribution. — This is an introduced form that has become widely 

 established throughout North America. 



Distribution in Maryland. — Statewide. 



Distinguishing characteristics. — Similar to R. rattus^ but differs in 

 being larger, heavier, and shorter tailed. In coloration it is grayish 

 or reddish brown on the back, heavily lined with black hairs along the 

 middorsal line. The belly is silvery gray, but in some specimens it may 

 be washed with a dingy yellowish - brown. Cranial differences between 

 this species and Rattus rattus are described under the latter species. 



