MAMMALS OF MARYLAND 



S3 



Distinguishing characteristics. — Teeth 2/3, 1/1, 1/2, 3/3, = 32; size 

 large, exceeded in Maryland only by the hoary bat; coloration uni- 

 formly dark brown; ears thick and heavy, somewhat rounded and 

 medium in size, naked except for some fur at the base; wings and inter- 

 femoral membrane lacking fur; skull larger and heavier than any other 

 local bat except Lasiurus cinereus, from which it differs in being notice- 

 ably narrower. Both Eptesicus and Lasiurus have 32 teeth, but in 

 Eptesicus there are 2 upper incisors and 1 upper premolar, while in 

 Lasiurus there are 2 upper premolars and 1 upper incisor on each side. 



Measurements. — External and cranial measurements of 15 adults 

 from Washington, D.C., are as follows: Total length 113.2 (110-122) ; 

 tail 43.6 (40^8) ; hind foot (average of 9) 12 (10-13) ; greatest length 

 of skull 18.5 (17.5-19.6) ; zygomatic breadth (average of 10) 12.6 

 (12.1-13.4); interorbital breadth 4.2 (3.9-4.5); length of maxillary 

 toothrow 7.1 (6.9-7.4). 



Habitat and habits. — This bat usually occurs around buildings and 

 dwellings where it roosts in the daytime under windowsills, in the eaves 

 of roofs, in cracks or crevices, or behind doors, blinds, and awnings. 

 It is sometimes found in hollow trees, under loose bark, and occasionally 

 in caves or crevices in cliffs. This species is common in parts of Mary- 

 land ; it is an unusual year when at least one specimen is not captured 

 in the Natural History building of the National Museum and added 

 to the study collection. The big brown bat does not form large colonies 

 as do some species of bats. Probably it is in part migratory, but does not 

 engage in extensive seasonal migrations, other than to find a suitable 

 place for hibernation. This is one of the last bats to hibernate in the 

 fall, and it is on wing again in early March. During mild spells of 

 winter it may be seen flying in the sun at midday (Hamilton, 1943, 

 p. 90). These bats are long-lived; records of banded animals recovered 

 10 to 15 years later are numerous. 



The homing instinct seems to be developed to some degree. Cohen 

 (1944) found several adults behind the shutter of a house in Berwyn, 

 Prince Georges County, and after banding them released them on 4 

 October 1941, in Baltimore City. Twelve days later, on 15 October 1941, 

 one of these bats was found hanging on the same shutter from which 

 it had been removed in Berwyn. It had travelled a distance of 26.56 

 miles, over the congested city of Baltimore, and heavily travelled high- 

 ways, to return to its home roost. 



The mating season for the big brown bat is September, and young are 

 born the following June. Normally two comprise a litter, although 

 there may occasionally be only one. The young grow rapidly and 3 or 

 4 weeks after birth are able to shift for themselves. 



This species, like all Maryland bats, is primarily insectivorous. 

 Hamilton (1933a) examined 2,200 summer fecal pellets from northern 



