THE PEST OF RATS 5 



itself in all the warmer parts of the world. It 

 is still prevalent in our South Atlantic States, 

 in the West Indies and in South America. The 

 tame white rats sold as pets are mostly of this 

 and the black species. 



In habits these three rats are similar, with 

 the important exception that the black rat and 

 the roof-rat (which some zoologists consider 

 merely varieties of one species), do not bur- 

 row under foundations, etc., as does the brown 

 rat. On the other hand they are far more 

 agile and addicted to climbing, a decided ad- 

 vantage in the tropics where a large part of 

 their food is obtained from trees, in whose 

 branches they frequently lodge their nests ; and 

 are less able to withstand cold than the brown 

 rat, which survives arctic winters in whaling 

 ships, apparently without distress. They are 

 also less prolific, having only ten mammaB to 

 the brown rat's twelve, and bearing on the 

 average only about five young at a birth to the 

 other's eight. This difference in prolificacy 

 alone would account for the great dominance 

 of the brown rat, at least in North America; 

 and it is to that species the rat, par excellence 



