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Show 324 THE NATIONAL GEOGRAPHIC MAGAZINE Photograph by Vernon Bailey THE FRINGED BAT (SEE TEXT, PAGE 33O) This is one of the Small-eared Bats, Myotis thysanodes, widely distributed over the southwestern United States and Mexico, and a regular inhabitant of caves. many have left for lower country and better feeding ground. On a warm evening in early May, about 10,000 came out of the cave-their numbers partly counted and partly estimated. From descriptions of the dense cloud of bats coming out in August, the numbers must run into hundreds of thousands, if not to millions, and such estimates would be necessary to account for the great deposits of guano taken out of the cave. The conditions of temperature, moisture, and space in this great cave seem to suit the bats better than those in any other of the numerous smaller and drier caves of the region. The enormous rooms in which they cling for their winter sleep to the ceiling 150 feet above the floor are very uniform in temperature, varying only from 55 to 60 degrees Fahrenheit, from early March with its freezing weather to hot days of May, and is said to show no noticeable difference in temperature throughout the year. The air of the cave is moist and heavy with the musky odor of bats, an odor that with a favorable wind can be detected outside half a mile from the entrance. To the bats this odor may be recognizable at a much greater distance and serve a very useful purpose in bringing them back from their nightly wanderings and from their seasonal migrations. GUANO DEPOSITS COLLECTED DURING THOUSANDS OF YEARS The guano deposits, composed entirely of insect remains, reach back into geologic ages, lying under huge stalagmites that have been thousands of years in forming. When first brought to commercial notice, in 1901, the guano filled some of the largest rooms to a depth of 100 feet, coming up nearly to the natural openings and sloping away for hundreds of yards over the cave floor. From all records now available, the estimates of 100,000 tons of guano taken out of the cave seem not too high. Most of this has been shipped to the California Fertilizer Company at San Bernardino, California, and sold at prices ranging from $20 to $75 a ton. The guano remaining in the cave would make but a few carloads, and most of it is old, mixed with earth, and of low grade as a fertilizer. A special effort was made to determine the rate of deposit of the guano, but with little satisfaction, because of the cold weather of March and April, the conse- |