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BULLETIN 1395, U. S. DEPARTMENT OF AGRICULTURE 



by F. C. Bishopp, in charge of the field station of the Bureau 

 oi Entomology, at Dallas, Tex., as follows : 



The Campbell bal roost consists of a sort of tower set on four posts about 10 

 feet above the ground. According to Doctor Campbell, the size of the roost 

 may be varied considerably. As I recall them, the dimensions of the roost at 

 Mitchell Lake arc about as follows: Twelve feet square at the bottom, the walls 

 slanting inward toward the top, which is about G feet square. Height, about 20 

 feet On the outside, the building is covered with drop siding with tar paper 

 beneath. The roof is shingled and projects over the edges. It is slightly ele- 

 vated so as to permit of the entrance and exit of the bats. Additional entry 

 space is allowed entirely down one side of the building. This opening, which 

 is about li 1 .. feet wide, is provided with boards slanting upward so as to 



exclude light to some extent hut allows 

 the bats to enter between them. The 

 central portion of the house from the 

 side provided with the entrance to the 

 opposite side is unobstructed from top 

 to bottom, thus leaving an air space 

 about 2y 2 feet wide. On each side of 

 the shaft, and running to the two other 

 sides of the building, is a series of 

 shelves made of matched flooring. 

 These shelves slant upward and out- 

 ward at an angle of about 30°. In the 

 first house constructed these shelves 

 were about 5 inches apart, but I believe 

 in the later model they are closer to- 

 gether. Wire netting is tacked on top 

 of each of the shelves so as to provide 

 places for the bats to hang. The slant 

 is given so as to allow the guano to 

 roll dow r n and drop into the center of 

 the bottom structure, which is provided 

 with trapdoors opening downward. 

 This is to permit of the emptying of the 

 manure into a wagon which is placed 

 under the roost. 



PlO. -°>. — Bat roost at Mitchell Lake, Tex., 

 occupied by a colony of Mexican free- 

 tailed bats, estimated on March 4, 1!»l' t, 

 to number 10,000, and yielding about 

 2 tons of guano a year. (Photo- 

 graph by Cbarles H. Sable) 



This roost when visited by Ver- 

 non Bailey, of the Biological Sur- 

 vey, in company with F. C. 

 Bishopp and Charles H. Gable, of 

 the Bureau of Entomology, on 

 March 4, 1924, was occupied by a large number of bats, all of the 

 species Tadarida mearicana. During the evening it was estimated 

 that about 10,000 bats flew from the roost in the half hour between 

 G.45 and 7.15 oxdock. They left so rapidly from both sides of the 

 tower that they could not be counted after the first five minutes. It 

 seemed probable that fully 10,000 were using the roost at that time. 

 Mr. Gable says that they were much more numerous in midsummer, 

 but none were seen there in winter, as, according to Doctor Campbell, 

 most of the bats disappear then and return early in spring, the first 

 sometimes appearing about the middle of February. 



About two tons of guano are taken from this roost every winter, 

 part of which is packed in 10-pound sacks and sold at $1 a sack to 

 local florists and individuals for use on house plants, and part of 

 it in larger lots to local gardeners at lower prices. This roost ap- 

 parently pays good dividends on the original cost and is considered 

 a valuable investment. It is the only one of five, however, con- 

 structed in and about San Antonio that has ever been extensively 



