Vol. V] TAYLOR— NEW SUBGENUS OF PHENACOMYS 15I 



we frequently find in the woods and under lone trees of this 

 variety, on the ground, small parts and at times almost, as 

 it appears, the entire nest." Wilder says that the tree mouse 

 seems to desert nests which have been disturbed, and has 

 found a few nests apparently permanently unoccupied. Nearly 

 all the nests examined by our party at Lierly's Ranch and at 

 Hearst were apparently deserted or unoccupied. Animals 

 were actually taken in eight out of 13 nests we carefully 

 investigated at Mendocino City. Of the five nests we found 

 to be unoccupied, some were doubtless deserted, while the dwell- 

 ers in the others may have been out at the time of our visits. 



Wilder has often noticed the disappearance of entire nests 

 previously located. This together with Todd's record of find- 

 ing portions of nests on the ground clearly indicates the pres- 

 ence of enemies of the tree mouse. Doubtless the small boy 

 is at present the chief of these. * Although there is nothing 

 definite on this head Mr. Wilder suggests cats and horned 

 owls as possible additional enemies. There is a possibility 

 also that unusual gales of wind may occasionally dislodge 

 the nests. 



10 BREEDING HABITS AND FAMILY RELATIONS 



(1) Time of breeding and size of families 

 On July 15 and 17 we found young in three nests at Men- 

 docino City. In each of two cases, there were two young, in 

 one case a single individual. Shelton took two young from 

 a nest at Spencer Butte, near Eugene, Oregon, on February 

 21. Wilder found a female and two half grown young in 

 Humboldt County, California, during the same month, and 

 asserts that the tree mice seem to breed all through the spring 

 and summer. Clay opened four nests containing three young 

 each, and says the breeding season seems to occur from the 

 middle of April till late in the summer. 



It may be that, like some species of Microtus, the young 

 may be born at any season, but it is perhaps more probable 

 that their birth is limited to late winter, spring and summer. 

 Two pairs of abdominal mammas are borne by the females, 

 which indicates that litters are small. 



The young are evidently helpless for some days after being 

 born, remaining for the time in the inner nest cavity. Young 

 in three out of the four nests investigated by Clay had not 

 yet opened their eyes. 



