Introducing Something New 119 



tails. The drastic lowering and raising of the lake exceeds the 

 tolerance of the plant so that the margins constantly recede 

 when high water has been prolonged, and they return when 

 a lower level is maintained. 



These examples show that plant changes, though infre- 

 quent, do take place in the marsh. But what about the mam- 

 mals? Are the changes of equal significance? I know of three. 

 One had taken place before my arrival, another occurred in 

 the past few years, while the third, if it has not taken place 

 already, will soon come and will greatly affect the local mam- 

 mal economy. 



The first change, which affected the marsh and every other 

 area where it took place, was the arrival of the Norway, or 

 brown, rat. We do not know when this creature came to the 

 Northwest but we know how it arrived, for it was a traveler 

 and a constant, though unwelcome, guest on ships. It may 

 have been unloaded in material shipped to this port or it may 

 have walked ashore under its own power. Once here we 

 may be sure that it increased rapidly in numbers and began its 

 history of destruction. In considering this pest we have the 

 satisfaction of knowing that it came of its own volition and 

 was not introduced because somebody thought that it would 

 become a good house pet or that it could be used as a check 

 on some greater pest. There is little good about the brown 

 rat, for when a creature is at once a carrier of serious diseases, 

 a destroyer of tremendous quantities of raw and finished ma- 

 terial, a predator on many useful wild and domestic birds 

 and mammals, and withal a foul and unclean animal, there 

 seems to be nothing left in its favor. Locally, it overruns the 

 marsh and is probably its greatest predator, doing much 

 damage to the eggs and young of the ground-nesting birds. 



The second mammal is the beaver, once a resident of the 

 entire Northwest, then almost eliminated by overlapping, 

 and now increasing in numbers. Its increase will pose many 

 problems in its relations with man. Its establishment in the 



