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6. August—Bats in Carlsbad Caverns
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104 | 6 { August Bats in Carlsbad Caverns The sweltering desert landscape of the American Southwest may not seem like an ideal wildlife-watching destination in August. But within the caves at Carlsbad Caverns National Park in New Mexico the temperatures can run 20–40 degrees cooler than the outside desert. That cool subterranean climate is ideal for the hundreds of thousands of Brazilian (a.k.a. Mexican) free-tailed bats that roost in the caves during the day. Come evening the bats awake and leave the cave in a mass exodus as they venture out into the desert to feed. Watching swarm after swarm of bats corkscrew their way up into the fading twilight and then depart toward the distant horizon is one of nature’s great wildlife-viewing spectacles. What’s Remarkable about Brazilian Free-Tailed Bats? every summer evening since time immemorial a half-million or so Brazilian free-tailed bats exit Carlsbad Caverns to head out into the surrounding desert to feed. upon leaving the cave the “clouds” of bats—yes, that is one of the terms for a group of bats—corkscrew upward into the evening sky in a counterclockwise pattern. Why counterclockwise? Some have speculated that this behavior is due to the Coriolis effect, the same earthly phenomenon that causes the water in your bathtub to drain in a counterclockwise pattern (assuming you live in the Northern Hemisphere). Although the Coriolis effect is extremely weak, a bat trying to gain altitude needs all the assistance it can get, so the ascending bats 105| August–Bats in Carlsbad Caverns may use it to more efficiently ascend. This counterclockwise pattern is so ingrained in bats they even use it in confined spaces such as inside houses. When the Carlsbad Caverns bats return to the cave at the end of the night they don’t need this earthly assistance to descend so they simply dive in a straight line into the cave entrance. Brazilian free-tailed bats leaving Carlsbad Caverns for their nighttime foraging. (Photo by Nickolay Hristov) [52.207.218.95] Project MUSE (2024-03-29 03:04 GMT) 106 | Summer Bat Echolocation In the blackness of a cave or on a moonless night eyesight is of little value to a flying bat. Therefore, bats have developed the fascinating skill of using echolocation to navigate and hunt. A bat emits a series of highfrequency clicks, inaudible to us. These high-frequency sounds bounce off objects in the bat’s flight path and are reflected back to the bat’s ears. The bat’s ears send the signals to the brain, which creates a virtual image of what’s in front of the bat. Of course this all happens almost instantly. In order to zero in on flying insects—the prey for most North American bat species—the clicking pulses the bat emits become more rapid and the pitch becomes higher. This echolocation, combined with the bat’s maneuverability , makes the bat a lethal predator of flying insects. By the time the night is over the insectivorous bat may have consumed over 50 percent of its own weight in bugs. Multiply that by the hundreds of thousands of bats exiting Carlsbad Caverns and that is a lot of free insect control. Bat Conservation As we continue to learn more about the mysterious lives of bats we realize just how vulnerable they are to man-made hazards. For example, it appears that many insect-eating bats suffered greatly from widespread pesticide use during the 1950s and 1960s. Fortunately, with better testing How are bats similar to butterflies? Starting in August huge numbers of recently hatched monarch butterflies migrate south from the central United States and Canada to the forested mountains of Mexico. Likewise, many species of bats also migrate to Mexico for the winter, including millions of Brazilian free-tailed bats that summer in and near US national parks. Fortunately, Mexico has established reserves and protected areas for these winter residents. As bats and butterflies both demonstrate, species conservation is often an international affair requiring protected areas and national parks on both sides of a border. 107| August–Bats in Carlsbad Caverns and regulation, pesticides are no longer a severe threat. An ongoing threat is cave disturbance. Careless or malicious people entering a cave can disturb bats, thereby causing the bats to leave their young, utilize precious energy reserves, and sometimes even abandon the cave. A relatively new threat to bats is wind turbines, which are popping up all...