380 



NORTH AMERICAN FAUNA 



[No. 55 



Generally they are found living in old buildings, under bark of 

 dead trees, in caves or cracks of cliffs, or seams of canyon walls, 

 where they hang up during the daylight hours. In winter they 

 seek the larger caves or walls of buildings, where a uniform tempera- 

 ture enables them to pass the cold season in a state of torpor, called 

 hibernation. 



At Eugene on June 21, 1914, these bats were actually numerous 

 along the river as they came out of the town at early dusk and flew 

 slowly over the water. In fact they flew so slowly that 4 specimens 

 were secured out ,of 6 shots, an unusual record for bat shooting, but 

 the slow flight was explained w r hen each of the 4 specimens was found 

 to contain a large foetus, practically ready for birth. The next 



day at Vida, farther up 

 the McKenzie Kiver, the 

 writer again found these 

 bats common but flying 

 so high over the treetops 

 that they were mostly out* 

 of shotgun range. A 

 dozen or 20 were often in 

 sight at one time, circling 

 and zigzagging in quest 

 of flying insects, but after 

 much shooting with heavy 

 loads only 2 were brought 

 down. On the evening of 

 June 26 they came down 

 and flew low enough for 

 a good series of specimens 

 to be secured, all of which proved to be females carrying each a fully 

 developed foetus which was fully a quarter of the size and weight 

 of the mother. No scales were available for weighing them, but the 

 size of the young as compared with that of the mother was astonish- 

 ing. With stomachs also distended with insects the old bats were 

 shaped like toads, and it was no wonder they flew slowly and high 

 up where the air was unobstructed. 



A few days earlier these bats had been found common on Spencer 

 Butte, near Eugene, where they flew so rapidly through the treetops 

 that no specimens were secured, and on July 18 at a 5,000-foot camp 

 at the north base of Three Sisters Peaks a few were collected as they 

 flew rapidly through the lodgepole pines, but these were all males 

 as were probably those on Spencer Butte. Also all but one of those 

 collected at McKenzie Bridge early in July were males. 



The young born in the latter part of June are soon able to fly and 

 catch their own food and by the middle of August are nearly full 

 grown. This is the mating season, and the males and females are 

 generally found together in about equal numbers. 



After the mating season the bats begin to store up fat for the 

 winter sleep and will often double in weight before the cold weather 

 begins. Very fat individuals will sometimes weigh up to 22 g. 



One of these bats collected by Luther J. Goldman at West Silver 

 Creek, 10 miles southwest of Silver Lake, on September 3, 1914, was 

 already very fat and probably ready for hibernation in the near 



FIGURE 97. Range of big brown bat, Eptcsicus fuscus 

 fuscus, in Oregon. 



