140 
JOURNAL OF MAMMALOGY 
rats invade cotton fields and carry off the cotton in order to secure 
the seed of which they are very fond. M. C. Rissinger, who for nine 
years has been stationed at the Eastside Heading on the main Imperial 
canal, reports finding a cache of cotton three feet in diameter that had 
been accumulated by a pair of cotton rats. The Colorado River 
species, therefore, has the same destructive habits as the related species 
of the gulf states. 
The Sonora beaver, one of the largest living rodents in North America, 
is common in the Colorado delta. This aquatic species was formerly 
common all along the Lower Colorado River, but has been greatly 
reduced in numbers by persistent trapping. It is still abundant in 
the lower delta region about Volcano Lake. Beavers have invaded 
the Imperial Valley along two different routes: by the Alamo River 
and main Imperial Canal on the east side of the delta, and by way of 
the Black Butte Canal on the west side. At the present time there 
are in the neighborhood of 100 beavers in the Imperial Valley north 
of the International Boundary. Nearly half of these are to be found 
in the Alamo River, whereas the others are scattered about in the 
larger canals. No beaver sign was noted along New River on the 
American side. A thriving colony has been established for some time 
on the Alamo within half a mile of the center of the town of Holtville. 
Four recently cut willow saplings were noted at this point on March 
25, 1921, and many willows, cut by beavers, have lodged against the 
trestle work of the Holton Interurban bridge west of Holtville. Serious 
breaks have already been caused by beavers burrowing into canal 
banks, and it is probable that other breaks will occur especially at 
points where the canals are built above the general land surface. 
Complaints of damage to canals by beavers have already been regis- 
tered from the Imperial Valley, and it is likely that this damage will 
increase. Beavers are protected by law at all seasons in California. 
The state law protecting them provides that, where they are endanger- 
ing the levees, permits to trap or remove them may be issued upon 
the proper application to the State Fish and Game Commission. 
However, if it were possible to remove all of the beavers from the 
American side of the boundary, it would only be a question of a short 
time until the canals would be reinfested from the breeding stock in 
Lower California since they have free access along all of the main 
canals, and beavers and muskrats do not need passports in crossing 
the International Boundary. While the fur of the Sonora beaver is 
short, pale and of poor quality, pelts of this animal sell for an average 
