184 



PROCEEDINGS OF THE NATIONAL MUSEUM 



2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 35 38 40 42 

 AGE IN DAYS 



Figure 21. — Average growth-rate of forearm in Plecotus iownsendii fallescens. Measure- 

 ments in millimeters. (Modified from Pearson, et al., 1952, p. 313.) 



The young probably nurse with their heads hanging down, and 

 most nursing must occur during the day, for from the time that they 

 are born or within a day or two of their bu'th, the young bats are left 

 in the roost at night while the adults go out to feed. Banding has 

 proved that each female bat unerringly selects her own young from 

 amongst the many in the cluster when she returns to the nursery 

 from her foraging flight. 



The young bats cling to anything that comes into their grasp, and 

 it is difficult to remove them from their mother. A disturbed mother 

 may sometimes be seen flying with a young-one dangling from a 

 nipple, but usually the young bat clings to its mother's fur with well- 

 clawed thumbs and feet, as well as to the nipple with its mouth. 

 Adults may fly with attached volant young weighing as much as six 

 grams — about two-thirds of the adult's weight. 



It is difficult to tell when lactation ceases, but it appears that 

 females nurse their young for about two months. By that time the 

 young are as large as their mothers and are skillful fliers. 



Molt: The young big-eared bat molts from its juvenile pelage to 

 adult pelage at about the time that it reaches adult body size, be- 

 tween the ages of one and two months. One collected on 7 August 

 at Burkes Garden, Va. (USNM 157075), was beginning the molt on 

 chest and belly. Three collected on Sand Creek, Wyo. (USNM), on 

 24 August, had barely begun to molt. 



Adults have a single complete molt annually, most commonly in 

 August. Possibly the molt normaUy occurs earlier in males than in 

 females. New hairs usually appear at almost the same time on all 



